As an aquatic engineer who has been designing facilities for many years, one of the more frequent questions I get from owners of indoor pools is “what can we do to get rid of nasty chlorine odors that our customers complain about?” Before I even look at their pool situation, I have a very good idea of the problems they face.

Whenever you have a indoor pool, which inherently has a confined air space surrounding the pool, that utilizes a chlorine based water treatment system, and you add people to the water who tend to sweat and produce other bodily fluids of various types (we will just leave it at that for now), you are going to generate odors from the water. When these odors include a strong chlorine smell, the culprit is the formation of chloramines in the pool water that are “off gassing” as water is stirred up during swimming activities or as water evaporates from the pool.

Swimming pools that use a chlorine-based disinfectant (most all pools fall into this category, even salt water chlorine generation pools) often experience a “chlorine odor” problem. When this problem gets bad enough, pool users will begin to complain of an offensive odor, skin and eye irritation, and even a burning sensation in the lungs. These issues can be present in any pool, but are particularly a problem with indoor pools because of the confined air space in the room.

Most people who encounter a pool with heavy “chlorine odors” immediately assume that the pool has too much chlorine in the water. To the contrary, the pool needs more chlorine and fewer chemical compounds known as chloramines. A pool in this condition needs to be super-chlorinated by the addition of much more chlorine in order for the pool water to return to proper chemical balance.

Since chloramines are not chemicals that we add to a pool for treatment of the water, we need to understand where they come from so that we can properly control their formation in the water.

Chloramines are chemical compounds that are formed when chlorine comes in contact with ammonia-nitrogen in various forms. This ammonia is introduced into the swimming pool through various sources, but the 3 most common sources in a pool are oils, sweat, and urine. Yes, you can now honestly now tell your kids that peeing in the pool does create a harmful chemical in the water, even if it doesn’t really turn blue around them per the myth they often hear. It may be wise however, to keep the blue water myth alive for your kids. I do.

To be more specific as to what causes the formation of chloramines we need to look briefly at the chemistry. When chlorine is added to water, two desirable chemicals are unleashed to disinfect the pool water:  hypochlorous acid, HOCl, and hypochlorite ion, OCl-. A measure of the chlorine in these two beneficial chemicals is known as “free available chlorine” or FAC. This is what we want in the pool to destroy germs and oxidize bad things in the water. When ammonia-nitrogen is added to the pool however, there are 3 possible chloramine compounds generated:

  1. When one of ammonia’s hydrogen ions is replaced with chlorine, monochloramine is formed.
  2. Replacing two hydrogen ions with chlorine produces dichloramine.
  3. Finally, it is possible to replace all three of ammonia’s hydrogen ions with chlorine to formtrichloramine.

Dichloramine and trichloramine are the two compounds that cause most of the odor and skin irritation problems.

So you may think the answer to solve the issues related to chloramine formation is simply not to use a chlorine-based treatment system for the pool water. However, for most swimming pools there really is no good alternative to chlorine disinfection products for the following reasons:

  1. Chlorine is relatively easy to use and cost effective.
  2. Chlorine is easy to measure in pool water.
  3. Chlorine is relatively stable in pool water.
  4. Chlorine has been used so long it’s use is well known and documented for pool operators.
  5. Chlorine is safe and effective within a fairly easy to maintain concentration range (recommended at around 1 to 4 ppm FAC)

So until there really is a better and more cost effective alternative to chlorine use in pools, we need to understand the things that can be done to control chloramine formation in the water.

Methods for controlling chloramines in pool water fall into 3 categories. The first category includes measures to keep chloramines from forming in the first place. The second category includes technologies for destroying them once they form in the water. The third category involves removing from around the pool the chloramine-contaminated air that causes odor and skin irritation. A combination of technologies from all three of these categories will generally result in the most pleasant to use swimming pools for swimmers.

Keep ammonia-nitrogen sources out of the pool

The first category of stopping the formation of chloramines involves keeping ammonia sources out of the pool as much as possible. Simple measures like requiring showers before entering the pool can help in this category. As most pool managers will attest, this is easier said than done.

It is advisable to post signs that remind patrons of the importance of being clean before entering the pool water. Most people will relate better to a discussion of the health benefits in this regard rather than a discussion of chloramines. A poster similar to the CDC’s “Six Steps for Healthy Swimming” may be a useful model for posted signs.

Two other potential sources of ammonia that are often overlooked are landscaping and deck cleaning. Most design regulations require water from decks to drain away from pools and not allow storm-water runoff or deck cleaning to drain into the pool. Pool operators should be aware of this potential ammonia source and eliminate the possibility of any such contamination of the pool, especially when using solvents to clean decks.

Break-up or destroy chloramines in pool water

The second category of destroying, or “breaking-up” the chloramines is a necessary strategy for any pool. For outdoor pools, where chloramine odors are not as much of a problem, you can simply super-chlorinate the pool when chloramine levels rise too high. This is a fairly straightforward procedure and all pool operators should be familiar with this process.

Other effective methods for destroying chloramines in water include introduction of ozone gas or ultraviolet (UV) light.

Ozone gas is a very reactive oxidizer, which will destroy chloramines and usually leave a residual amount of ozone to re-enter the pool. The trick with ozone is to apply just enough to deal with the chloramines, without reacting negatively with anything else around the pool, such as pool plaster.

UV light, applied in proper dosages through specialized equipment, is a very effective way to break down chloramine compounds as well.

Remove chloramine laced air from the pool area

The third category includes methods for removing chloramine compounds from the room atmosphere once they are airborne.  Methods in this category are almost exclusively utilized on indoor pools because with outdoor pools the air drifts away naturally so chloramine odors are not as noticeable.  Although air removal for an outdoor pool does not make sense, it must be noted that chloramine concentrations must also be controlled in outdoor pools so that effective disinfection of the pool continues and other water chemistry parameters of the pool stay in proper balance.

For an indoor pool however, chloramine buildup can reach intolerable levels quickly. The more a pool is utilized, the quicker the build-up of chloramines will occur.

Two methods for removing these airborne particles include fresh air exchanges in the room in a wholesale manner through the HVAC system, and newly developed methods to remove chloramine laced air from more localized areas at the pool surface.

The first method of using the HVAC system to supply fresh outdoor air exchanges to the entire room is expensive because of having to constantly heat and adjust humidity of the resulting large volume of new air coming from outside the room.

Since chloramine laced air is heavier than normal air in the swimming pool room, it tends to stay close to the pool surface where it was created in the first place. Because of this, it is difficult, if not impossible, to design a “whole room” air handling system that effectively removes the chloramine saturated air in a heavily used pool. Often times the actual result of taking the “whole room air exchange” approach alone is that the nasty, heavier air is mixed with the cleaner lighter air above, and the offensive air is then spread throughout the room, making the issue even worse.

A newer method of removing smaller amounts of air from just above the water surface before chloramines spread throughout the room is proving to be more effective. Replacing a smaller volume of air just at the water surface has the added benefit of costing less to heat and condition the replacement air since the volume of air being exchanged is much lower compared to a whole room exchange.

One piece of equipment that has hit the market lately to remove air from just above the water surface, where chloramines first become airborne and tend to hang because of their weight relative to cleaner air, is called the “Evacuator“. For more information on this innovative approach to indoor pool air quality, please read our article on the subject.

Conclusions on controlling chlorine odors in swimming pools

In conclusion, outdoor pool chloramine control is often best achieved by super-chlorination when levels get too high. Since the chlorine smell and skin/eye irritation will be less an issue with outdoor air circulation, other costlier methods to control chloramine formation or chloramine destruction are hard to justify from a cost standpoint.

Conversely, for indoor pools it is advisable to employ methods to control chloramine concentrations before they reach the point of requiring super-chlorination. When it gets to the point of requiring super-chlorination it is likely that there are many unhappy pool users, and the pool operating staff will hear plenty about the chlorine smell. UV, or possibly a tightly controlled ozone feed, are good technologies to consider. Proper design of air handling through room HVAC and installation of a system to remove chloramines closer to the pool water surface are also imperative to achieving great air quality for your patrons.

The worst possible outcome is to build a fancy new indoor pool complex that looks great but smells terrible. Close attention to design of systems for the control of chloramine concentrations is money well spent. From a veteran aquatic facility design engineer, I recommend use of proven systems and not necessarily the ones with the best and flashiest marketing materials.  Don’t be the guinea pig for anyone’s new wiz-bang gizmo. Your end users don’t care about nice marketing materials, they only care about how pleasant your facility is to use.

Designed and constructed properly, your new aquatic facility will be praised by everyone, especially your end users!
As an Aquatic Design Consultants Inc.” href=”//waterparkteam.com/” target=”_blank”>aquatic engineer who has been designing facilities for many years, one of the more frequent questions I get from owners of indoor pools is “what can we do to get rid of nasty chlorine odors that our customers complain about?” Before I even look at their pool situation, I have a very good idea of the problems they face.

Whenever you have a indoor pool, which inherently has a confined air space surrounding the pool, that utilizes a chlorine based water treatment system, and you add people to the water who tend to sweat and produce other bodily fluids of various types (we will just leave it at that for now), you are going to generate odors from the water. When these odors include a strong chlorine smell, the culprit is the formation of chloramines in the pool water that are “off gassing” as water is stirred up during swimming activities or as water evaporates from the pool.

Swimming pools that use a chlorine-based disinfectant (most all pools fall into this category, even salt water chlorine generation pools) often experience a “chlorine odor” problem. When this problem gets bad enough, pool users will begin to complain of an offensive odor, skin and eye irritation, and even a burning sensation in the lungs. These issues can be present in any pool, but are particularly a problem with indoor pools because of the confined air space in the room.

Most people who encounter a pool with heavy “chlorine odors” immediately assume that the pool has too much chlorine in the water. To the contrary, the pool needs more chlorine and fewer chemical compounds known as chloramines. A pool in this condition needs to be super-chlorinated by the addition of much more chlorine in order for the pool water to return to proper chemical balance.

Since chloramines are not chemicals that we add to a pool for treatment of the water, we need to understand where they come from so that we can properly control their formation in the water.

Chloramines are chemical compounds that are formed when chlorine comes in contact with ammonia-nitrogen in various forms. This ammonia is introduced into the swimming pool through various sources, but the 3 most common sources in a pool are oils, sweat, and urine. Yes, you can now honestly now tell your kids that peeing in the pool does create a harmful chemical in the water, even if it doesn’t really turn blue around them per the myth they often hear. It may be wise however, to keep the blue water myth alive for your kids. I do.

To be more specific as to what causes the formation of chloramines we need to look briefly at the chemistry. When chlorine is added to water, two desirable chemicals are unleashed to disinfect the pool water:  hypochlorous acid, HOCl, and hypochlorite ion, OCl-. A measure of the chlorine in these two beneficial chemicals is known as “free available chlorine” or FAC. This is what we want in the pool to destroy germs and oxidize bad things in the water. When ammonia-nitrogen is added to the pool however, there are 3 possible chloramine compounds generated:

  1. When one of ammonia’s hydrogen ions is replaced with chlorine, monochloramine is formed.
  2. Replacing two hydrogen ions with chlorine produces dichloramine.
  3. Finally, it is possible to replace all three of ammonia’s hydrogen ions with chlorine to formtrichloramine.

Dichloramine and trichloramine are the two compounds that cause most of the odor and skin irritation problems.

So you may think the answer to solve the issues related to chloramine formation is simply not to use a chlorine-based treatment system for the pool water. However, for most swimming pools there really is no good alternative to chlorine disinfection products for the following reasons:

  1. Chlorine is relatively easy to use and cost effective.
  2. Chlorine is easy to measure in pool water.
  3. Chlorine is relatively stable in pool water.
  4. Chlorine has been used so long it’s use is well known and documented for pool operators.
  5. Chlorine is safe and effective within a fairly easy to maintain concentration range (recommended at around 1 to 4 ppm FAC)

So until there really is a better and more cost effective alternative to chlorine use in pools, we need to understand the things that can be done to control chloramine formation in the water.

Methods for controlling chloramines in pool water fall into 3 categories. The first category includes measures to keep chloramines from forming in the first place. The second category includes technologies for destroying them once they form in the water. The third category involves removing from around the pool the chloramine-contaminated air that causes odor and skin irritation. A combination of technologies from all three of these categories will generally result in the most pleasant to use swimming pools for swimmers.

Keep ammonia-nitrogen sources out of the pool

The first category of stopping the formation of chloramines involves keeping ammonia sources out of the pool as much as possible. Simple measures like requiring showers before entering the pool can help in this category. As most pool managers will attest, this is easier said than done.

It is advisable to post signs that remind patrons of the importance of being clean before entering the pool water. Most people will relate better to a discussion of the health benefits in this regard rather than a discussion of chloramines. A poster similar to the CDC’s “Six Steps for Healthy Swimming” may be a useful model for posted signs.

Two other potential sources of ammonia that are often overlooked are landscaping and deck cleaning. Most design regulations require water from decks to drain away from pools and not allow storm-water runoff or deck cleaning to drain into the pool. Pool operators should be aware of this potential ammonia source and eliminate the possibility of any such contamination of the pool, especially when using solvents to clean decks.

Break-up or destroy chloramines in pool water

The second category of destroying, or “breaking-up” the chloramines is a necessary strategy for any pool. For outdoor pools, where chloramine odors are not as much of a problem, you can simply super-chlorinate the pool when chloramine levels rise too high. This is a fairly straightforward procedure and all pool operators should be familiar with this process.

Other effective methods for destroying chloramines in water include introduction of ozone gas or ultraviolet (UV) light.

Ozone gas is a very reactive oxidizer, which will destroy chloramines and usually leave a residual amount of ozone to re-enter the pool. The trick with ozone is to apply just enough to deal with the chloramines, without reacting negatively with anything else around the pool, such as pool plaster.

UV light, applied in proper dosages through specialized equipment, is a very effective way to break down chloramine compounds as well.

Remove chloramine laced air from the pool area

The third category includes methods for removing chloramine compounds from the room atmosphere once they are airborne.  Methods in this category are almost exclusively utilized on indoor pools because with outdoor pools the air drifts away naturally so chloramine odors are not as noticeable.  Although air removal for an outdoor pool does not make sense, it must be noted that chloramine concentrations must also be controlled in outdoor pools so that effective disinfection of the pool continues and other water chemistry parameters of the pool stay in proper balance.

For an indoor pool however, chloramine buildup can reach intolerable levels quickly. The more a pool is utilized, the quicker the build-up of chloramines will occur.

Two methods for removing these airborne particles include fresh air exchanges in the room in a wholesale manner through the HVAC system, and newly developed methods to remove chloramine laced air from more localized areas at the pool surface.

The first method of using the HVAC system to supply fresh outdoor air exchanges to the entire room is expensive because of having to constantly heat and adjust humidity of the resulting large volume of new air coming from outside the room.

Since chloramine laced air is heavier than normal air in the swimming pool room, it tends to stay close to the pool surface where it was created in the first place. Because of this, it is difficult, if not impossible, to design a “whole room” air handling system that effectively removes the chloramine saturated air in a heavily used pool. Often times the actual result of taking the “whole room air exchange” approach alone is that the nasty, heavier air is mixed with the cleaner lighter air above, and the offensive air is then spread throughout the room, making the issue even worse.

A newer method of removing smaller amounts of air from just above the water surface before chloramines spread throughout the room is proving to be more effective. Replacing a smaller volume of air just at the water surface has the added benefit of costing less to heat and condition the replacement air since the volume of air being exchanged is much lower compared to a whole room exchange.

One piece of equipment that has hit the market lately to remove air from just above the water surface, where chloramines first become airborne and tend to hang because of their weight relative to cleaner air, is called the “Evacuator“. For more information on this innovative approach to indoor pool air quality, please read our article on the subject.

Conclusions on controlling chlorine odors in swimming pools

In conclusion, outdoor pool chloramine control is often best achieved by super-chlorination when levels get too high. Since the chlorine smell and skin/eye irritation will be less an issue with outdoor air circulation, other costlier methods to control chloramine formation or chloramine destruction are hard to justify from a cost standpoint.

Conversely, for indoor pools it is advisable to employ methods to control chloramine concentrations before they reach the point of requiring super-chlorination. When it gets to the point of requiring super-chlorination it is likely that there are many unhappy pool users, and the pool operating staff will hear plenty about the chlorine smell. UV, or possibly a tightly controlled ozone feed, are good technologies to consider. Proper design of air handling through room HVAC and installation of a system to remove chloramines closer to the pool water surface are also imperative to achieving great air quality for your patrons.

The worst possible outcome is to build a fancy new indoor pool complex that looks great but smells terrible. Close attention to design of systems for the control of chloramine concentrations is money well spent. From a veteran aquatic facility design engineer, I recommend use of proven systems and not necessarily the ones with the best and flashiest marketing materials.  Don’t be the guinea pig for anyone’s new wiz-bang gizmo. Your end users don’t care about nice marketing materials, they only care about how pleasant your facility is to use.

Designed and constructed properly, your new aquatic facility will be praised by everyone, especially your end users!
Ahhh….there is nothing better than summer recreation at a modern municipal swimming pool. Fun at the pool is a tradition as American as apple pie and baseball. Come to think of it, it has probably surpassed both of these in the hearts of most people.

The City of Belton, Missouri is not a lot different from other American cities with 24,000 residents. The residents take great pride in where they live and want to make their community the best it can be for their families. The schools are great, it is a safe and clean city, and they have many wonderful park and recreation offerings that enrich their lives.

Until the summer of 2011 though, one thing they did not have was a nice outdoor swimming pool where they could enjoy that great American pastime of outdoor fun in the sun at a city pool.

Oh, they had an old outdoor pool, but it was not much of a pleasure to use.  Constructed in 1967, the rectangular shaped pool had many problems that made its use a lackluster experience at best.

From the physical deterioration of the old pool, decks and bathhouse, to its lack of anything really fun to do (even the old diving boards had to be removed for safety reasons), it had just become a “worn out” and boring pool. It was much more fun for residents to enjoy Belton’s great indoor pools at the community center than to visit the old and deteriorated outdoor pool.

Still, there is just something about being outdoors enjoying the sunshine and a nice swimming pool that kept gnawing at residents. Finally, after much discussion, a property tax measure was put on the ballot to build a new outdoor swimming pool along with several other improvements to the City’s parks.

In November of 2010, residents overwhelmingly approved the property tax measure, and the design team of Aquatic Design Consultants, Inc. and WNB Architects began design of a new, recreationally focused, outdoor aquatic facility to bring summertime pool fun back to Belton.

Below is a video of the end product:


One of the great challenges of this project was the tight budget we had for pool construction. Since the property tax measure included many park related improvements in addition to the swimming pool,our pool construction budget was capped at $1.7 million (not including bathhouse renovations.) We were challenged to design a high impact, waterpark style facility that would have a capacity for 450 people at a time.
Our other challenge was to design the facility, receive bids for construction, and have the facility completed and open for use by July 4th, 2011. This gave us just eight months, mostly during the nasty winter weather, to accomplish all of these tasks. Do I hear anybody saying, challenge?

Nothing gets our design team pumped up like a great challenge that requires maximum creativity and veteran aquatic facility knowledge to succeed. We were primed and ready to make things happen. Without skipping a beat (with this schedule there were no beats to spare), we dove headlong into the project.

After design was complete, a local commercial pool builder with an excellent reputation in the business, KC Gunite, was awarded the project as low bidder for construction. As a veteran designer I cannot even begin to tell you how critical it is to have a highly qualified pool builder on such a project. Suffice it to say, without a qualified pool builder; success is much harder, if not impossible, to come by.

The other key player in this project was the owner. As the representative for the City, Todd Spalding,Belton’s Parks and Recreation Director, was the perfect person to have for a successful project as ambitious as this one.

To say the least, Todd was tenacious at getting permits in place and owner decisions made quickly and effectively. He authorized expenditures judiciously and wisely, as if it were his own money. You know things are going to go well when everyone on the team, from the owner to the designers and contractors, are all positive, “can do “ people. Todd is as “can do” as they come.

The end result of everyone’s efforts is a beautiful facility that has blown away all of the expectations the Belton residents had. The facility is concisely located were the old pool was demolished and includes many modern waterpark style amenities such as:

  • Premium slide complex with a tube slide and speed slide sharing a single tower
  • Lazy river traversing through the entire facility
  • Zero depth, beach style entry area
  • Children’s shallow-water interactive play structure with slide
  • Underwater bench areas for parents to relax and watch the kids
  • Floating obstacle course
  • Water basketball and volleyball area
  • Shade structures throughout the facility and in some water areas
  • Comfortable deck furnishings for resting and relaxing
  • Renovated bathhouse facilities with concessions
  • Modern filtration and automated treatment systems to keep the water clean and safe for users

The facility is an absolute gem for the residents of Belton. It also fits well into the City’s overall park master plan. In the future, as population grows, a larger outdoor facility will be constructed. Even at that time, this facility has been designed to fit perfectly within the City’s overall aquatic facility offerings.

For more information about this project you may want to contact our design firm or Todd Spaldingwith the City of Belton. For specifics about the facility, such as hours of operation and location, please visit their website.
Ahhh….there is nothing better than summer recreation at a modern municipal swimming pool. Fun at the pool is a tradition as American as apple pie and baseball. Come to think of it, it has probably surpassed both of these in the hearts of most people.

The City of Belton, Missouri is not a lot different from other American cities with 24,000 residents. The residents take great pride in where they live and want to make their community the best it can be for their families. The schools are great, it is a safe and clean city, and they have many wonderful park and recreation offerings that enrich their lives.

Until the summer of 2011 though, one thing they did not have was a nice outdoor swimming pool where they could enjoy that great American pastime of outdoor fun in the sun at a city pool.

Oh, they had an old outdoor pool, but it was not much of a pleasure to use.  Constructed in 1967, the rectangular shaped pool had many problems that made its use a lackluster experience at best.

Family fun at the new swimming pool in Belton Missouri

Family fun at the new swimming pool in Belton Missouri

From the physical deterioration of the old pool, decks and bathhouse, to its lack of anything really fun to do (even the old diving boards had to be removed for safety reasons), it had just become a “worn out” and boring pool. It was much more fun for residents to enjoy Belton’s great indoor pools at the community center than to visit the old and deteriorated outdoor pool.

Still, there is just something about being outdoors enjoying the sunshine and a nice swimming pool that kept gnawing at residents. Finally, after much discussion, a property tax measure was put on the ballot to build a new outdoor swimming pool along with several other improvements to the City’s parks.

In November of 2010, residents overwhelmingly approved the property tax measure, and the design team of Aquatic Design Consultants, Inc. and WNB Architects began design of a new, recreationally focused, outdoor aquatic facility to bring summertime pool fun back to Belton.

Below is a video of the end product:

One of the great challenges of this project was the tight budget we had for pool construction. Since the property tax measure included many park related improvements in addition to the swimming pool,our pool construction budget was capped at $1.7 million (not including bathhouse renovations.) We were challenged to design a high impact, waterpark style facility that would have a capacity for 450 people at a time.

Our other challenge was to design the facility, receive bids for construction, and have the facility completed and open for use by July 4th, 2011. This gave us just eight months, mostly during the nasty winter weather, to accomplish all of these tasks. Do I hear anybody saying, challenge?

Nothing gets our design team pumped up like a great challenge that requires maximum creativity and veteran aquatic facility knowledge to succeed. We were primed and ready to make things happen. Without skipping a beat (with this schedule there were no beats to spare), we dove headlong into the project.

After design was complete, a local commercial pool builder with an excellent reputation in the business, KC Gunite, was awarded the project as low bidder for construction. As a veteran designer I cannot even begin to tell you how critical it is to have a highly qualified pool builder on such a project. Suffice it to say, without a qualified pool builder; success is much harder, if not impossible, to come by.

Lazy River at the Belton Aquatic Park

Lazy River at the Belton Aquatic Park

The other key player in this project was the owner. As the representative for the City, Todd Spalding,Belton’s Parks and Recreation Director, was the perfect person to have for a successful project as ambitious as this one.

To say the least, Todd was tenacious at getting permits in place and owner decisions made quickly and effectively. He authorized expenditures judiciously and wisely, as if it were his own money. You know things are going to go well when everyone on the team, from the owner to the designers and contractors, are all positive, “can do “ people. Todd is as “can do” as they come.

The end result of everyone’s efforts is a beautiful facility that has blown away all of the expectations the Belton residents had. The facility is concisely located were the old pool was demolished and includes many modern waterpark style amenities such as:

Zero Depth Entry at the Belton Aquatic Park

Zero Depth Entry at the Belton Aquatic Park

  • Premium slide complex with a tube slide and speed slide sharing a single tower
  • Lazy river traversing through the entire facility
  • Zero depth, beach style entry area
  • Children’s shallow-water interactive play structure with slide
  • Underwater bench areas for parents to relax and watch the kids
  • Floating obstacle course
  • Water basketball and volleyball area
  • Slide complex at the Aquatic Center

    Slide complex at the Aquatic Center

    Shade structures throughout the facility and in some water areas

  • Comfortable deck furnishings for resting and relaxing
  • Renovated bathhouse facilities with concessions
  • Modern filtration and automated treatment systems to keep the water clean and safe for users

The facility is an absolute gem for the residents of Belton. It also fits well into the City’s overall park master plan. In the future, as population grows, a larger outdoor facility will be constructed. Even at that time, this facility has been designed to fit perfectly within the City’s overall aquatic facility offerings.

For more information about this project you may want to contact our design firm or Todd Spaldingwith the City of Belton. For specifics about the facility, such as hours of operation and location, please visit their website.
This is one of the most misunderstood topics I know of when it comes to swimming pool construction. Let me start out by stating a fact that everyone should know:

All of these products are concrete!

Shotcrete, “concrete”, and gunite are all basically the same product with variations in strength, inherent water-tightness, and methods of construction.

I don’t know how many times I have heard people who are looking to build a new aquatic facility tell me that they want a concrete pool and not a gunite pool, or that they want a shotcrete pool and not a concrete pool.

The first thing everyone needs to know is that these three terms, that are thrown around so carelessly, are actually different forms of concrete with different strengths and weaknesses as it relates to swimming pool construction.

The second thing you should know is that each type of concrete has important applications when it comes to aquatic facility construction. Limiting the design of your facility to just one of these three technologies just because a “pool designer” or someone else told you a particular product is the best, without knowing the facts for yourself, is a mistake many facility owners make. This article is intended to shed some much needed light on this subject so that aquatic facility owners, or potential owners, can make the wisest possible decisions that are in their best interests.

The many myths about shotcrete and gunite not being “concrete” pools actually originate with designers who just don’t know how to design good concrete pool structures other than cast-in-place, and contractors who cannot build shotcrete or gunite concrete pools. This is unfortunate since each type of concrete has its place, and knowledge of how to design and construct each will result in the best possible swimming pool structures that are very strong and watertight.

Concrete is basically man’s version of making a very strong rock. Various forms of concrete have been in existence since the time of the Assyrians. The Roman Empire made great strides in constructing many types of structures out of crude, but effective, forms of concrete.

Concrete, or manmade rock, is created by using small pieces of natural rock in various forms and sizes that we refer to as aggregate. To form concrete, this aggregate is mixed with some sort of bonding material that holds all of the smaller rock particles together and solidifies into a usable structure of the dimensions needed. The overall strength of the manmade rock, or concrete, depends on how effective the bonding material is at binding the aggregate together.

In ancient times the bonding materials used to form concrete consisted of elements like clay, lime, or gypsum. In 1824 Joseph Aspdin invented what is called Portland cement as a new and much more effective bonding material. Improved and perfected formulations of Portland cement are what we use today as the bonding material that holds aggregate together to form very strong “concrete”.

For any type of construction, including that of swimming pools, the differences in concrete come from the specific formulas we, as engineers, design. In a modern and typical concrete formula, there are four basic categories of materials, cement, aggregate, water, and admixture chemicals. During the design process, we create formulas for concrete to meet the needed application and the structural performance we require from the concrete.

Each time I design an aquatic center, I customize the various concrete formulas to meet the strength and water-tightness characteristics I require for the swimming pools. While designing the concrete formulas, I take into consideration the aggregate materials available in the geographic area of the aquatic center and the type of concrete application that best fits the project, shotcrete, gunite, and/or cast-in-place concrete. All three of these concrete construction methods will be described in detail as part of this article.

In swimming pool design, we are concerned with two main performance categories related to concrete for our pool walls and floors. These performance categories are strength and water-tightness. Most of the problems I have seen over the years with concrete pool structures relate to the lack of understanding of how to properly design concrete formulas that result in strong and watertight swimming pools.

So, now that I have given you a basic overview of concrete, we need to explore the differences between shotcrete, gunite, and “cast-in-place” concrete. Cast-in-place concrete is what most people mean when they say “concrete”.

 

“Cast-in-place” Concrete

Cast-in-place concrete is the category of concrete that is installed by building a form, usually out of wooden boards, and then pouring the wet and runny concrete mixture into the form before using tools to smooth out the surface. The concrete then dries, through the act of water hydration, and hardens into the structure. In the case of an aquatic facility, our concrete structures are typically floors, walls, decks, and sometimes elements like diving platforms, water slides, water play features, or hard landscape items around the swimming pools.

Installing concrete by the “cast-in-place” method is one of the most common practices in the entire construction industry and is therefore comfortable to many designers and contractors.

Please keep in mind however, a very important point here. Just because doing something over and over the same way may be “comfortable” to a contractor or designer does not necessarily make the procedure the best application when building a swimming pool that must be strong and watertight. The use of cast-in-place concrete does have a place in pool construction, but in most cases, shotcrete or gunite should be used as well for the best possible result.

One of the drawbacks to using cast-in-place concrete for everything in swimming pools comes from the fact that the concrete mixture for cast-in-place has to contain a large volume of water so that it can be poured into the forms. Being able to “pour” the concrete is critical to getting the proper thickness of concrete in all places and to be able to smooth out the surface of the concrete.

The real problem with having a large volume of water in the concrete is that to form hard concrete the water reacts with the cement in the concrete mixture to cause high heat during the act of hydration. This high heat causes the water to evaporate from the concrete with a resulting decrease in overall volume of the concrete as it hardens.

This decrease in concrete volume is a characteristic of concrete formation and something that concrete designers must be aware of. To account for this volume loss, we must design joints between concrete sections of the pool in order to control cracking in the concrete. In swimming pools unfortunately, having joints or cracks is not at all desirable when we are trying to make pools watertight.

Having joints in a concrete pool is unavoidable if the pool is large. Proper design of joints, which includes waterproofing materials of various sorts, between concrete sections can result in nice watertight pools, at least initially. However, over time most joints must be maintained properly in order to remain waterproof. If the joint is poorly designed or constructed, which happens way more than you may think in this industry, the joint has the potential of being a huge source of water loss.

Water loss around or under a pool is undesirable for many reasons such as the cost of wasted water and chemicals, or the creation of subsurface voids under the pool structure when migration of leaking water removes supporting soils. Voids in and around pools can cause pools to actually break apart or decks and piping around the pools to settle or break.

A rule of thumb to remember when designing swimming pools is to minimize the number of separation joints between concrete sections in the pool!

Of the three methods of concrete construction, cast-in-place tends to be the most expensive for swimming pools. The main reason for this comes from the fact that forming, pouring, and finishing cast-in-place requires more labor and materials.

On the positive side, cast-in-place, when constructed on a horizontal plane such as on a pool floor, will result in the most uniform surface of the three methods. That is why most aquatic designers will utilize cast-in-place concrete for pool floors.

Pros and Cons of “cast-in-place” concrete

Pros:

      • It is hands down the most common type of concrete construction. This means that most contractors have experience with concrete installation using this technique.
      • If designed properly, which is a big if from what I have seen during my design career, cast-in-place concrete can result in a strong and waterproof structure, when considering the concrete surface itself and not the joints between concrete sections. Typical compressive strengths of the concrete in cast-in-place pools are 4,000 to 5,000 psi.
      • If properly designed and constructed, this form of concrete results in a relatively smooth surface that with proper preparation can readily accept epoxy-based pool painting systems. If cast-in-place is used for verticals walls, care must be taken however, to eliminate pitting that often occurs when forms are removed from the pool-side of the wall. These pits must be filled and smoothed with materials that are compatible with the concrete and the finish surface treatment of paint or plaster.
      • When used for pool floors, cast-in-place concrete results in the most uniform surfaces possible. Since a pool floor does not have a form for the top surface, pitting, as a result of form removal, is not an issue. Cast-in-place is actually the best method for most pool floors because of these facts.

Cons:

      • The biggest drawback to exclusively using cast-in-place concrete in a swimming pool is the amount of water that has to be used in the concrete mix formula so that the concrete can be “poured” into the forms. This results in a large number of separation joints between pool sections when compared with the other concrete types; shotcrete and gunite.
      • Strong concrete, but it is the weakest of the three methods.
      • With cast-in-place, it is harder and much more complicated to form shapes other than straight rectangles. Most modern swimming pools have various shapes and curves to add character, interest, and greater functionality to the designs. With shotcrete or gunite such shapes are constructed easily.
      • Cast-in-place is generally more expensive to construct than shotcrete or gunite.

 

Shotcrete Concrete

Both shotcrete and gunite are what is referred to as “free form” applications of concrete. Free form, by its very nature, enables concrete to be used to create very strong and watertight structures following any type of geometry. The concrete can be applied horizontally or vertically and can even be shot upward to adhere and form to the underside of a ceiling.

Shotcrete and gunite products have been used since the turn of the 20th century in applications such a tunnels through mountains for roadways. Many of the interstate tunnels you may have driven through were constructed using these forms of concrete.

Shotcrete is a form of concrete that is applied pneumatically through the use of a pump, hose, and a specially designed application nozzle. The formula for concrete in a shotcrete application has a higher amount of cement and a lower amount of water than that of “cast-in-place” concrete. The formula results in a concrete mix that is dry enough to be applied to vertical surfaces such as pool walls.

Shotcrete concrete is often times referred to as “wet gun” concrete. The reason for this moniker is the way shotcrete is applied compared to the other pneumatic concrete method called gunite. Gunite is often referred to as “dry gun” concrete.

With shotcrete, the entire concrete mixture is combined at the concrete plant, including the water in the mixture, before being transported to the jobsite in concrete trucks. This is the same procedure that is used for cast-in-place concrete with the exception of the lower water content in the shotcrete mixture.

Once the concrete arrives at the jobsite, it is poured into the shotcrete pump and sprayed under pressure into place in layers through a back-and-forth motion of the nozzle. The shotcrete application continues until the designed wall thickness is achieved.

The result of using shotcrete for swimming pool walls is a much stronger wall with fewer joints between wall sections, than with a cast-in-place wall.

One thing that must be considered when using shotcrete in pools is the experience factor. It is critical with any construction that the contractor building the pool be highly experience with the methods of construction being used. With shotcrete, the person operating the shotcrete hose and nozzle is the absolute key to getting a great result from the concrete.

When done properly, shotcrete results in a much stronger and watertight installation than with cast-in-place. If constructed incorrectly, any form of concrete work, including all three methods, will be disastrous. It is imperative that the swimming pool contractor hired for the concrete work be highly experienced with the chosen method of concrete construction.

Pros and Cons of shotcrete concrete

Pros:

      • When properly designed and constructed, shotcrete (or gunite, which will be discussed next) will result in the strongest and most watertight concrete pools possible.
      • Because of the lower volume of water used in the concrete mixture, there is less volume change from water hydration, which results in much fewer joints in the pool. Remember the rule of thumb for good pool design and construction is to “minimize the number of pool joints between concrete sections in the pool.”
      • Higher compressive strengths than cast-in-place concrete. Typical compressive strengths of shotcrete are in the range of 6,000 to 7,500 psi.
      • “Free form” application makes it possible to build very strong and watertight structures of any shape.

The many myths about shotcrete and gunite not being “concrete” pools actually originate with designers who just don’t know how to design good concrete pool structures other than cast-in-place, and contractors who cannot build shotcrete or gunite concrete pools. This is unfortunate since each type of concrete has its place, and knowledge of how to design and construct each will result in the best possible swimming pool structures that are very strong and watertight.

Cons:

      • Like all concrete installation, the contractor must be experienced and skilled in the particular technique of installation. There are fewer people skilled in the use of shotcrete than that of cast-in-place concrete.
      • The finished surface of shotcrete is generally a bit rougher than with cast-in-place concrete. Because of this, most shotcrete pools have a finished surface consisting of a pool plaster material or Diamond Brite as opposed to epoxy-based pool paint. It is not that epoxy pool paint is better than pool plaster, it is just a fact that paints generally will not look as good when applied to shotcrete walls as opposed to cast-in-place or gunite concrete with a smoother finish. Most people prefer pool plaster type finishes, but epoxy paint is generally cheaper to initially install. (Pool surfaces will be covered in a future article)
      • Few pool designers actually understand how to properly design shotcrete or gunite in swimming pool structures. The only reason this is listed as a con is the fact that the number of truly qualified concrete pool designers is limited to a few. It is more an indictment of limited design knowledge than it is of shotcrete or gunite concrete.

 

Gunite Concrete

Like shotcrete, gunite is a form of concrete that is applied to a surface pneumatically. The formula for concrete in a gunite application has a higher percentage of cement and a lower amount of water than that of “cast-in-place” or “shotcrete” concrete. Like shotcrete, the formula results in a concrete mix that is dry enough to be applied to vertical surfaces such as pool walls.

Gunite concrete is often times referred to as “dry gun” concrete.  The reason for this label is the dry nature of its application. Unlike cast-in-place and shotcrete, with gunite the dry portions of the concrete are mixed at a concrete plant, or at the jobsite, before being applied. There is no water added to the dry concrete mix until actual application from the gunite nozzle.

Gunite equipment forces the dry concrete mixture into a hose under air pressure. The dry mixture travels through the hose to a specialized nozzle that is also connected to a water source under pressure. The dry concrete is combined with the water and mixed through channels in the nozzle before being sprayed onto a preformed surface. The result is a concrete mixture that can be applied extremely dry with a high cement content to bind the aggregate with even greater strength.

Like with shotcrete, the gunite nozzle operator uses a back-and-forth motion to sculpt the pool walls to the shape and thicknesses designed.

As has been discussed in depth already, the lower volume of water in gunite results in smaller changes in the concrete volume as it hydrates, with a resulting need for much fewer joints.

Like shotcrete, one thing that must be considered when using gunite in pools is the experience factor. It is critical with any construction that the contractor building the pool be highly experience with the methods of construction being used. With gunite, the person operating the gunite hose and nozzle is the absolute key to getting a great result from the concrete.

When done properly, gunite results in a much stronger and watertight installation than with cast-in-place. Gunite will result in even stronger concrete than shotcrete.

If constructed or designed incorrectly, any form of concrete work, including all three methods, will be disastrous. It is imperative that the pool contractor hired for the concrete work be highly experienced with the chosen method of concrete construction.

Pros and Cons of gunite concrete

Pros:

      • When properly designed and constructed, gunite will result in the strongest and most watertight concrete pools possible.
      • Because of the lower volume of water used in the concrete mixture, there is less volume change through water hydration, which results in much fewer joints in the pool. Remember the rule of thumb for good pool design and construction is to “minimize the number of pool joints between concrete sections in the pool.”
      • Higher compressive strengths than cast-in-place or shotcrete concrete. Typical compressive strengths of gunite are in the range of 7,500 to 9,000 psi.
      • Properly constructed gunite has a smooth enough surface to be finished by epoxy-based paints or pool plasters.
      • “Free form” application makes it possible to build very strong and watertight structures of any shape.

The many myths about shotcrete and gunite not being “concrete” pools actually originate with designers who just don’t know how to design good concrete pool structures other than cast-in-place, and contractors who cannot build shotcrete or gunite concrete pools. This is unfortunate since each type of concrete has its place, and knowledge of how to design and construct each will result in the best possible swimming pool structures that are very strong and watertight.

Cons:

      • Like all concrete installation, the contractor must be experienced and skilled in the particular technique of installation. There are even fewer people skilled in the use of gunite than that of cast-in-place or shotcrete concrete.
      • Construction of pools using the gunite process is somewhat more time consuming than shotcrete, which usually results in a slightly higher construction cost.
      • Few pool designers actually understand how to properly design gunite or shotcrete in swimming pool structures. The only reason this is listed as a con is the fact that the number of truly qualified concrete pool designers is limited to a few. It is more an indictment of limited design knowledge than it is of gunite or shotcrete concrete.

 

Conclusions and Recommendations for use of Shotcrete, Gunite, or Cast-In-Place Concrete in Swimming Pools

I need to begin this section by saying that every swimming pool or waterpark design is different and the types of structures used for each application need to be customized to meet the individual needs of each facility.

That being said, it is hard to beat a swimming pool structure that is concrete. Properly designed and constructed, concrete pools will last many decades with very little upkeep expense related to the structure.

Most of the pools we have designed over the years are concrete.  Generally, the only time we use other materials for pool structures is when pool structure weight is a critical consideration, as is sometimes the case with pool construction in high-rise buildings. Even in these applications, we have designed several concrete pools in elevated buildings throughout the years. Each situation needs to be fully evaluated before deciding on the best construction techniques for the swimming pools.

Our typical design utilizes cast-in-place concrete for pool floors, in order to get a good uniform surface for pool users to walk on, with shotcrete or gunite concrete for the pool walls in order to get very strong and watertight construction with few pool joints. Generally, the only time we use cast-in-place walls is when there is not a competent pool contractor with a good proven track record of pneumatically applied concrete walls available for the job.

My recommendation for you is to hire a real aquatic engineer who knows how to design every type of pool structure possible. If you talk with an “aquatic designer” who tells you one particular type of pool structure is the only way to go, find another pool designer, or better yet, call me, Kevin McElyea, PE at 913-937-0025. I will gladly help you.

This is one of the most misunderstood topics I know of when it comes to swimming pool construction. Let me start out by stating a fact that everyone should know:

All of these products are concrete!

Shotcrete, “concrete”, and gunite are all basically the same product with variations in strength, inherent water-tightness, and methods of construction.

I don’t know how many times I have heard people who are looking to build a new aquatic facility tell me that they want a concrete pool and not a gunite pool, or that they want a shotcrete pool and not a concrete pool.

The first thing everyone needs to know is that these three terms, that are thrown around so carelessly, are actually different forms of concrete with different strengths and weaknesses as it relates to swimming pool construction.

The second thing you should know is that each type of concrete has important applications when it comes to aquatic facility construction. Limiting the design of your facility to just one of these three technologies just because a “pool designer” or someone else told you a particular product is the best, without knowing the facts for yourself, is a mistake many facility owners make. This article is intended to shed some much needed light on this subject so that aquatic facility owners, or potential owners, can make the wisest possible decisions that are in their best interests.

The many myths about shotcrete and gunite not being “concrete” pools actually originate with designers who just don’t know how to design good concrete pool structures other than cast-in-place, and contractors who cannot build shotcrete or gunite concrete pools. This is unfortunate since each type of concrete has its place, and knowledge of how to design and construct each will result in the best possible swimming pool structures that are very strong and watertight.

Concrete is basically man’s version of making a very strong rock. Various forms of concrete have been in existence since the time of the Assyrians. The Roman Empire made great strides in constructing many types of structures out of crude, but effective, forms of concrete.

Concrete, or manmade rock, is created by using small pieces of natural rock in various forms and sizes that we refer to as aggregate. To form concrete, this aggregate is mixed with some sort of bonding material that holds all of the smaller rock particles together and solidifies into a usable structure of the dimensions needed. The overall strength of the manmade rock, or concrete, depends on how effective the bonding material is at binding the aggregate together.

In ancient times the bonding materials used to form concrete consisted of elements like clay, lime, or gypsum. In 1824 Joseph Aspdin invented what is called Portland cement as a new and much more effective bonding material. Improved and perfected formulations of Portland cement are what we use today as the bonding material that holds aggregate together to form very strong “concrete”.

For any type of construction, including that of swimming pools, the differences in concrete come from the specific formulas we, as engineers, design. In a modern and typical concrete formula, there are four basic categories of materials, cement, aggregate, water, and admixture chemicals. During the design process, we create formulas for concrete to meet the needed application and the structural performance we require from the concrete.

Each time I design an aquatic center, I customize the various concrete formulas to meet the strength and water-tightness characteristics I require for the swimming pools. While designing the concrete formulas, I take into consideration the aggregate materials available in the geographic area of the aquatic center and the type of concrete application that best fits the project, shotcrete, gunite, and/or cast-in-place concrete. All three of these concrete construction methods will be described in detail as part of this article.

In swimming pool design, we are concerned with two main performance categories related to concrete for our pool walls and floors. These performance categories are strength and water-tightness. Most of the problems I have seen over the years with concrete pool structures relate to the lack of understanding of how to properly design concrete formulas that result in strong and watertight swimming pools.

So, now that I have given you a basic overview of concrete, we need to explore the differences between shotcrete, gunite, and “cast-in-place” concrete. Cast-in-place concrete is what most people mean when they say “concrete”.

 

“Cast-in-place” Concrete

Cast-in-place concrete is the category of concrete that is installed by building a form, usually out of wooden boards, and then pouring the wet and runny concrete mixture into the form before using tools to smooth out the surface. The concrete then dries, through the act of water hydration, and hardens into the structure. In the case of an aquatic facility, our concrete structures are typically floors, walls, decks, and sometimes elements like diving platforms, water slides, water play features, or hard landscape items around the swimming pools.

During construction - Cast-in-place concrete floors await Gunite concrete walls

During construction – Cast-in-place concrete floors await Gunite concrete walls

Installing concrete by the “cast-in-place” method is one of the most common practices in the entire construction industry and is therefore comfortable to many designers and contractors.

Please keep in mind however, a very important point here. Just because doing something over and over the same way may be “comfortable” to a contractor or designer does not necessarily make the procedure the best application when building a swimming pool that must be strong and watertight. The use of cast-in-place concrete does have a place in pool construction, but in most cases, shotcrete or gunite should be used as well for the best possible result.

One of the drawbacks to using cast-in-place concrete for everything in swimming pools comes from the fact that the concrete mixture for cast-in-place has to contain a large volume of water so that it can be poured into the forms. Being able to “pour” the concrete is critical to getting the proper thickness of concrete in all places and to be able to smooth out the surface of the concrete.

The real problem with having a large volume of water in the concrete is that to form hard concrete the water reacts with the cement in the concrete mixture to cause high heat during the act of hydration. This high heat causes the water to evaporate from the concrete with a resulting decrease in overall volume of the concrete as it hardens.

This decrease in concrete volume is a characteristic of concrete formation and something that concrete designers must be aware of. To account for this volume loss, we must design joints between concrete sections of the pool in order to control cracking in the concrete. In swimming pools unfortunately, having joints or cracks is not at all desirable when we are trying to make pools watertight.

Having joints in a concrete pool is unavoidable if the pool is large. Proper design of joints, which includes waterproofing materials of various sorts, between concrete sections can result in nice watertight pools, at least initially. However, over time most joints must be maintained properly in order to remain waterproof. If the joint is poorly designed or constructed, which happens way more than you may think in this industry, the joint has the potential of being a huge source of water loss.

Water loss around or under a pool is undesirable for many reasons such as the cost of wasted water and chemicals, or the creation of subsurface voids under the pool structure when migration of leaking water removes supporting soils. Voids in and around pools can cause pools to actually break apart or decks and piping around the pools to settle or break.

A rule of thumb to remember when designing swimming pools is to minimize the number of separation joints between concrete sections in the pool!

Of the three methods of concrete construction, cast-in-place tends to be the most expensive for swimming pools. The main reason for this comes from the fact that forming, pouring, and finishing cast-in-place requires more labor and materials.

On the positive side, cast-in-place, when constructed on a horizontal plane such as on a pool floor, will result in the most uniform surface of the three methods. That is why most aquatic designers will utilize cast-in-place concrete for pool floors.

Pros and Cons of “cast-in-place” concrete

Pros:

      • It is hands down the most common type of concrete construction. This means that most contractors have experience with concrete installation using this technique.
      • If designed properly, which is a big if from what I have seen during my design career, cast-in-place concrete can result in a strong and waterproof structure, when considering the concrete surface itself and not the joints between concrete sections. Typical compressive strengths of the concrete in cast-in-place pools are 4,000 to 5,000 psi.
      • If properly designed and constructed, this form of concrete results in a relatively smooth surface that with proper preparation can readily accept epoxy-based pool painting systems. If cast-in-place is used for verticals walls, care must be taken however, to eliminate pitting that often occurs when forms are removed from the pool-side of the wall. These pits must be filled and smoothed with materials that are compatible with the concrete and the finish surface treatment of paint or plaster.
      • When used for pool floors, cast-in-place concrete results in the most uniform surfaces possible. Since a pool floor does not have a form for the top surface, pitting, as a result of form removal, is not an issue. Cast-in-place is actually the best method for most pool floors because of these facts.

Cons:

      • The biggest drawback to exclusively using cast-in-place concrete in a swimming pool is the amount of water that has to be used in the concrete mix formula so that the concrete can be “poured” into the forms. This results in a large number of separation joints between pool sections when compared with the other concrete types; shotcrete and gunite.
      • Strong concrete, but it is the weakest of the three methods.
      • With cast-in-place, it is harder and much more complicated to form shapes other than straight rectangles. Most modern swimming pools have various shapes and curves to add character, interest, and greater functionality to the designs. With shotcrete or gunite such shapes are constructed easily.
      • Cast-in-place is generally more expensive to construct than shotcrete or gunite.

 

Shotcrete Concrete

Both shotcrete and gunite are what is referred to as “free form” applications of concrete. Free form, by its very nature, enables concrete to be used to create very strong and watertight structures following any type of geometry. The concrete can be applied horizontally or vertically and can even be shot upward to adhere and form to the underside of a ceiling.

Shotcrete and gunite products have been used since the turn of the 20th century in applications such a tunnels through mountains for roadways. Many of the interstate tunnels you may have driven through were constructed using these forms of concrete.

Shotcrete is a form of concrete that is applied pneumatically through the use of a pump, hose, and a specially designed application nozzle. The formula for concrete in a shotcrete application has a higher amount of cement and a lower amount of water than that of “cast-in-place” concrete. The formula results in a concrete mix that is dry enough to be applied to vertical surfaces such as pool walls.

Shotcrete concrete is often times referred to as “wet gun” concrete. The reason for this moniker is the way shotcrete is applied compared to the other pneumatic concrete method called gunite. Gunite is often referred to as “dry gun” concrete.

With shotcrete, the entire concrete mixture is combined at the concrete plant, including the water in the mixture, before being transported to the jobsite in concrete trucks. This is the same procedure that is used for cast-in-place concrete with the exception of the lower water content in the shotcrete mixture.

Once the concrete arrives at the jobsite, it is poured into the shotcrete pump and sprayed under pressure into place in layers through a back-and-forth motion of the nozzle. The shotcrete application continues until the designed wall thickness is achieved.

The result of using shotcrete for swimming pool walls is a much stronger wall with fewer joints between wall sections, than with a cast-in-place wall.

One thing that must be considered when using shotcrete in pools is the experience factor. It is critical with any construction that the contractor building the pool be highly experience with the methods of construction being used. With shotcrete, the person operating the shotcrete hose and nozzle is the absolute key to getting a great result from the concrete.

When done properly, shotcrete results in a much stronger and watertight installation than with cast-in-place. If constructed incorrectly, any form of concrete work, including all three methods, will be disastrous. It is imperative that the swimming pool contractor hired for the concrete work be highly experienced with the chosen method of concrete construction.

Pros and Cons of shotcrete concrete

Pros:

      • When properly designed and constructed, shotcrete (or gunite, which will be discussed next) will result in the strongest and most watertight concrete pools possible.
      • Because of the lower volume of water used in the concrete mixture, there is less volume change from water hydration, which results in much fewer joints in the pool. Remember the rule of thumb for good pool design and construction is to “minimize the number of pool joints between concrete sections in the pool.”
      • Higher compressive strengths than cast-in-place concrete. Typical compressive strengths of shotcrete are in the range of 6,000 to 7,500 psi.
      • “Free form” application makes it possible to build very strong and watertight structures of any shape.

The many myths about shotcrete and gunite not being “concrete” pools actually originate with designers who just don’t know how to design good concrete pool structures other than cast-in-place, and contractors who cannot build shotcrete or gunite concrete pools. This is unfortunate since each type of concrete has its place, and knowledge of how to design and construct each will result in the best possible swimming pool structures that are very strong and watertight.

Cons:

      • Like all concrete installation, the contractor must be experienced and skilled in the particular technique of installation. There are fewer people skilled in the use of shotcrete than that of cast-in-place concrete.
      • The finished surface of shotcrete is generally a bit rougher than with cast-in-place concrete. Because of this, most shotcrete pools have a finished surface consisting of a pool plaster material or Diamond Brite as opposed to epoxy-based pool paint. It is not that epoxy pool paint is better than pool plaster, it is just a fact that paints generally will not look as good when applied to shotcrete walls as opposed to cast-in-place or gunite concrete with a smoother finish. Most people prefer pool plaster type finishes, but epoxy paint is generally cheaper to initially install. (Pool surfaces will be covered in a future article)
      • Few pool designers actually understand how to properly design shotcrete or gunite in swimming pool structures. The only reason this is listed as a con is the fact that the number of truly qualified concrete pool designers is limited to a few. It is more an indictment of limited design knowledge than it is of shotcrete or gunite concrete.

 

Gunite Concrete

Like shotcrete, gunite is a form of concrete that is applied to a surface pneumatically. The formula for concrete in a gunite application has a higher percentage of cement and a lower amount of water than that of “cast-in-place” or “shotcrete” concrete. Like shotcrete, the formula results in a concrete mix that is dry enough to be applied to vertical surfaces such as pool walls.

Swimming pool construction - Pneumatically applied concrete walls form flexible curve shapes

During construction – Pneumatically applied concrete walls form flexible curve shapes

Gunite concrete is often times referred to as “dry gun” concrete.  The reason for this label is the dry nature of its application. Unlike cast-in-place and shotcrete, with gunite the dry portions of the concrete are mixed at a concrete plant, or at the jobsite, before being applied. There is no water added to the dry concrete mix until actual application from the gunite nozzle.

Gunite equipment forces the dry concrete mixture into a hose under air pressure. The dry mixture travels through the hose to a specialized nozzle that is also connected to a water source under pressure. The dry concrete is combined with the water and mixed through channels in the nozzle before being sprayed onto a preformed surface. The result is a concrete mixture that can be applied extremely dry with a high cement content to bind the aggregate with even greater strength.

Like with shotcrete, the gunite nozzle operator uses a back-and-forth motion to sculpt the pool walls to the shape and thicknesses designed.

As has been discussed in depth already, the lower volume of water in gunite results in smaller changes in the concrete volume as it hydrates, with a resulting need for much fewer joints.

Like shotcrete, one thing that must be considered when using gunite in pools is the experience factor. It is critical with any construction that the contractor building the pool be highly experience with the methods of construction being used. With gunite, the person operating the gunite hose and nozzle is the absolute key to getting a great result from the concrete.

When done properly, gunite results in a much stronger and watertight installation than with cast-in-place. Gunite will result in even stronger concrete than shotcrete.

If constructed or designed incorrectly, any form of concrete work, including all three methods, will be disastrous. It is imperative that the pool contractor hired for the concrete work be highly experienced with the chosen method of concrete construction.

Pros and Cons of gunite concrete

Pros:

      • When properly designed and constructed, gunite will result in the strongest and most watertight concrete pools possible.
      • Because of the lower volume of water used in the concrete mixture, there is less volume change through water hydration, which results in much fewer joints in the pool. Remember the rule of thumb for good pool design and construction is to “minimize the number of pool joints between concrete sections in the pool.”
      • Higher compressive strengths than cast-in-place or shotcrete concrete. Typical compressive strengths of gunite are in the range of 7,500 to 9,000 psi.
      • Properly constructed gunite has a smooth enough surface to be finished by epoxy-based paints or pool plasters.
      • “Free form” application makes it possible to build very strong and watertight structures of any shape.

The many myths about shotcrete and gunite not being “concrete” pools actually originate with designers who just don’t know how to design good concrete pool structures other than cast-in-place, and contractors who cannot build shotcrete or gunite concrete pools. This is unfortunate since each type of concrete has its place, and knowledge of how to design and construct each will result in the best possible swimming pool structures that are very strong and watertight.

Cons:

      • Like all concrete installation, the contractor must be experienced and skilled in the particular technique of installation. There are even fewer people skilled in the use of gunite than that of cast-in-place or shotcrete concrete.
      • Construction of pools using the gunite process is somewhat more time consuming than shotcrete, which usually results in a slightly higher construction cost.
      • Few pool designers actually understand how to properly design gunite or shotcrete in swimming pool structures. The only reason this is listed as a con is the fact that the number of truly qualified concrete pool designers is limited to a few. It is more an indictment of limited design knowledge than it is of gunite or shotcrete concrete.

 

Lazy river construction

Lazy river during construction – Cast-in-place concrete floor with curve gunite concrete walls

Conclusions and Recommendations for use of Shotcrete, Gunite, or Cast-In-Place Concrete in Swimming Pools

I need to begin this section by saying that every swimming pool or waterpark design is different and the types of structures used for each application need to be customized to meet the individual needs of each facility.

That being said, it is hard to beat a swimming pool structure that is concrete. Properly designed and constructed, concrete pools will last many decades with very little upkeep expense related to the structure.

Most of the pools we have designed over the years are concrete.  Generally, the only time we use other materials for pool structures is when pool structure weight is a critical consideration, as is sometimes the case with pool construction in high-rise buildings. Even in these applications, we have designed several concrete pools in elevated buildings throughout the years. Each situation needs to be fully evaluated before deciding on the best construction techniques for the swimming pools.

Our typical design utilizes cast-in-place concrete for pool floors, in order to get a good uniform surface for pool users to walk on, with shotcrete or gunite concrete for the pool walls in order to get very strong and watertight construction with few pool joints. Generally, the only time we use cast-in-place walls is when there is not a competent pool contractor with a good proven track record of pneumatically applied concrete walls available for the job.

My recommendation for you is to hire a real aquatic engineer who knows how to design every type of pool structure possible. If you talk with an “aquatic designer” who tells you one particular type of pool structure is the only way to go, find another pool designer, or better yet, call me, Kevin McElyea, PE at 913-937-0025. I will gladly help you.

Maintaining clean and safe water for the users of our swimming pools, and aquatic facilities of all types, is the most important thing we, as facility owners, operators, and designers, can do.

Any aquatic facility that has lived through the nightmare of people getting sick, because of the water they came in contact with at their facility, can attest to the fact that constant water quality vigilance is an absolute MUST. (A recent article about an outbreak in the Cincinnati Area discusses such a nightmare.)

Note – If you really want to see statistics showing how common such outbreaks are, visit the CDC website for annual summary reports.)

The most important factor to maintaining clean and safe water is the type of equipment being used to treat and maintain the water.

When you have been an aquatic engineer as long as I have, you see a lot of products introduced to the market over the years. Although many of these products are introduced with great fanfare and slick marketing materials, the simple truth is that most do not perform as advertised. As a veteran designer in the aquatics industry, I have become immune to the hype and drawn to the effective.

Executive Summary

If your facility installs the following equipment, you can be assured you have the most state-of-the-art tools possible to keep your pool water clean and safe for your end users:

1. Great swimming pool water filtration, such as with regenerative media filters

2. UV treatment

3. Chloramine evacuator system (indoor pools only)

4. Chlorine water treatment (solid, liquid, or salt, combined with automated chemical controls and proper pH adjustment equipment)

With this equipment installed, and vigilance by pool operations staff at maintaining proper water chemistry balance, you will have the safest water possible for your swimmers.

The purpose of this article is to simply “cut to the chase” and lay out for you the true and proven state-of-the-art in swimming pool water treatment today. The following list represents the very best complete system you can deploy for the cleanest and safest swimming pool water possible:

1. Great filtration of the water

In the filtration category today, regenerative media filtration is one of the best available. It is not initially the cheapest, but it provides the best filtration possible at a low operating cost.

This filter will remove extremely small particles that are dangerous to swimmers and a cause of cloudy water.  The media used in these filters, perlite or diatomaceous earth (DE), is capable of removing particles as small as 1 micron from the water. Configured properly, this type of filtration is capable of removing many nasty microorganisms, such as the dreaded cryptosporidium.

Small particles that remain in the water are also costly because of unnecessary consumption of disinfection chemicals. Utilizing great filtration equipment will decrease chemical usage costs.

2. Secondary water treatment – Ultraviolet (UV) Light Treatment

Installing a properly sized UV system, in addition to a great filter, will effectively kill all of the nasty bacteria, viruses, and cysts that can make people sick. UV will also effectively break down chloramines that form in the pool water. UV is one of the best investments you can make in controlling sickness outbreaks at your facility while reaping a side benefit of maintaining cleaner water.

3. Chloramine air evacuation (indoor pools only) – Evacuator located near pool water surface

Since chloramines will form in the chlorinated water when people enter the pool, chlorine odor and equipment corrosion issues will occur. Even though a UV system will break down chloramines as they travel through the light chamber, chloramines will still form once the water re-enters a swimming pool with people in it.

The most effective way to prevent chlorine odor/sickness and equipment corrosion issues is to evacuate the contaminated air from a location just above the pool water surface and exhaust it outside of the building. An evacuator unit (installed as close to the water surface as possible) that is synchronized with the room’s HVAC system is the best way to eliminate offensive/dangerous/corrosive air issues.

4. Primary water treatment – Chlorine

No matter how you cut the deck, chlorine is the best primary treatment chemical for swimming pools. It really does not matter what form you use, calcium hypochlorite (solid), sodium hypochlorite (liquid), chlorine generator (salt), or chlorine gas (dangerous and hardly ever used these days), chlorine is relatively safe and stable for swimming pool use.

As a side note, chlorine concentrations lower than have traditionally been used are safe when all of the other systems described in this article are used. Many regulatory authorities have yet to officially lower chlorine residual requirements however, so you must follow the guidelines for your jurisdiction.