Concrete Pool Problems
This article is intended to help you understand more about common concrete pool problems so that you can know what to look for, and what these problems mean for the future of the pool. Also covered are some commonly asked questions about concrete swimming pools. There is a lot of misinformation floating around both on the internet and in the real world about concrete pools. As a (retired) concrete pool builder this article is accurate from an industry insiders perspective, and will help you to understand fact from fiction when it comes to concrete pools. Once you have these concrete pool facts straight we can look more deeply into common problems associated with concrete pools.
Concrete Pools VS. Gunite Pools - Concrete pools is the name for the top of the category. Gunite is a specific method for placing concrete, as is shotcrete. Placement of concrete simply means exactly as it sounds...the method used to put the concrete where it needs to be. The significance of this is that, for the most part, a concrete pool is a concrete pool. It does not matter if it is a gunite pool, or a shotcrete pool, or a cast pool. These are all concrete pools and for all intents and purposes they are the same. If you built a pool by hand would you call it a "wheelbarrow and shovel pool"? No, probably not. In the same sense, there is little value in defining a pool as shotcrete or gunite. Sure there are minute technical differences in each application, but ultimately each are a type of concrete pool and that is what is significant.
How Long Do Concrete Pools Last - This is a loaded question that you need a technical mind to understand. In the most simple of terms, consider a concrete swimming pool like a new car. So now the question is, how long do new cars last? Obviously the answer to that question will depend on a long list of variables about how much the car is used, where the car is stored, the weather it is exposed to, whether it receives regular maintenance and check ups etc. and the list goes on and on. The answer to the question how long do concrete pools last, is around 50 to 70 years as a service life for the shell, assuming no major failures happen along the way. Concrete pools can even last longer than this with modern day concrete, steel grids, water proofing and engineering standards, so it is possible that some of the pools being built today can still be within their service life up to 100 years from now. How long a specific concrete pool will last has absolutely everything to do with how well it is serviced, maintained and cared for over the years...just like with a car.
Concrete Pool Components - A concrete pool shell is usually poured (or shot) as one continuous concrete pour. A finished product concrete pool however has multiple individual components which are the shell, the coping, the tile band, the interior surface, and of course, the plumbing / the filtration system. If you want to know more about concrete pool problems then this is how you begin to break down the pool into individual components.
Concrete Pool Shell Problems
If there is a problem that you want to avoid with a concrete pool, this is it. A cracked concrete pool shell is one of the worst case scenarios for a concrete pool (other than popping out of the ground, and yes a concrete pool can pop out of the ground). Any problems with the shell of a concrete pool are ones you want to avoid, and while cracking is the ultimate concern, there are also other concerns with concrete pool shells. Another problem is the shell can begin to sink on one side. This could be from a leak eroding the ground on one side of the pool, or it could be that the pool was built on uncompacted ground or multiple ground types that resulted in uneven settling over time.
The entire benefit of a concrete pool is that the shell is so strongly built. The average concrete pool is built stronger, thicker and with more steel that the foundation for the house that is sitting next to it. When you start to experience failures or deficiencies in the shell, the concern is that almost all repair avenues will be prohibitively expensive. Fortunately concrete pools have another benefit over other pool types which is the fact that they are very serviceable. What this means is that, even when it comes to the shell, you can almost always service (repair) a concrete pool.
Concrete Pool Cracks - A crack in the shell of a concrete pool indicates an error in installing the pool and placing the concrete, or it means changing local conditions put an unbearable stress load on the shell. Much like a chain, a concrete pool shell is only as strong as the weakest link. Fortunately it takes a lot of force to crack a concrete pool shell and so this is a fairly rare problem. Most commonly a concrete pool shell will crack in the first three days after placing the shell, or at a future point in time if the pool settles, shifts or sinks not in uniform. If the concrete for the shell is placed with too much water in the mix this can cause a weakened shell strength as well as contraction cracking as the water actuates the cure. A concrete pool shell that has cracked shortly after pouring should be tested for strength to determine the cause.
Sinking Or Shifting Pools - Uniform movement in the ground is important for a concrete pool. If one end of the pool moves and the other does not, this results in a structural crack. The most common causes for this type of structural crack would be from a long term leak eroding the soil on one end of the pool, which causes only one end to sink. The next most common reason would be from a pool that was built on uncompacted soil, or partially built on two or more ground conditions. For example you would not want to build a concrete pool half on sand and half on bedrock as this can allow for different rates of settling over time that can result in structural cracking.
If you have a problem with your concrete pool shell it is important to differentiate whether this is a old problem that is static and no longer changing, or if this problem is still getting worse. Static cracks in a concrete pool can be repaired, and there are also repair options for a pool that is no longer level in the ground, so long as it is no longer moving. If the pool is still moving, or if the cracks are migrating, then no repairs that you make to the shell will stop the problem. You need to find out what is causing the cracking problem and fix that first. In almost every case this will be traced back to a leak in the pool.
Concrete Pool Coping Problems
The coping on a concrete pool is the area of the pool deck that sits directly on top of the vertical pool wall. Remember that concrete pools are thick, and most are around one foot of concrete thick along the top of the wall. When you build a concrete pool, the pool needs to be isolated from the deck surrounding the pool. The concrete shell of the pool is usually finished one to four inches lower than the finished deck elevation will be. This allows you to install a finished top edge dimension to the pool, but also allows for a bond break between the pool shell and the deck surrounding the pool. In the event that a bond break and coping is not installed on a concrete pool, or installed improperly, then it is very likely the top of the pool walls will suffer damage from something called bond shear.
First, on a concrete pool there is something called a bond beam. A bond beam is a horizontal area of increased strength located at the top of the pool wall where the pool structure is the weakest. In this area of the pool there is thicker concrete and more steel than any other area in the pool. This gives the same effect that a rim on a bowl would have in that it provides structural integrity and reinforcement to help hold the top of the vertical structure stable. Bond sheer is one of the single most common problems for concrete pools in areas that get freeze and thaw conditions in the winter or pools that deal with any extreme heat and sun.
Bond Sheer in Concrete Pools - If a concrete pool coping is not isolated from the deck area surrounding the pool then forces from the deck moving horizontally can be transferred to the weakest part of the pool at the top of the wall. When exposed to differences in temperature like from the heat of summer to cold of winter, a pool deck might have to endure substantial changes in physical size due to expansion and contraction. This temperature differential can result in 100 linear feet of concrete expanding and contracting by up to 3/4". If the horizontal deck is not isolated with an expansion joint, and protected by a mastic sealer, then when the pool deck shifts it will crack the top of the pool wall.
Pool Coping Delamination - Many pool coping systems are natural or manufactured stone that is mortar set (or epoxied) into place. A common pool coping problem is to have the coping stones delaminate and begin to shift or move when you walk on them. In addition to this being a safety hazard this also can cause the tiles near to the coping to pop off from the movement of the coping stones. Delaminated coping is also more likely to allow for a deck sheer situation to result in freezing conditions due to water getting in behind and under the coping where is can weaken the concrete over time.
A pool deck should be isolated from pool coping by a mastic joint or flexible urethane. This is one of the most commonly overlooked maintenance items for concrete pools as it can be deceiving as to how important this little rubber joint is. New mastic joint sealer should be applied every seven to ten years, depending on where you live and the amount of harsh weather your pool is exposed to. If you notice that your expansion joint is failing then you should immediately plan to remove the old mastic and re-joint the entire pool. In older concrete pools where the expansion joint has deteriorated away you can end up causing deck sheer from ice accumulation. In winter conditions the area where the expansion joint should be will fill with water. When this water freezes you have effectively connected the coping to the deck with ice. now if the deck shifts (or expands) this force will be transferred to the top of the pool wall where a crack can easily develop. This, or the force of the water itself freezing into ice can cause the deck shear force on the pool wall.
Concrete Pool Tile Problems
Tiles in concrete pools are installed at the top of the pool wall along the waterline. Tiles are installed here since they are extremely resistant to staining. Since oils float on water, if you did not have a tile band it would be very easy to develop, and see, a scum line along the water surface. Perimeter tiles in a pool provide both a visual distraction from the accumulation of scum and debris on top of the water, as well as providing an easy to clean surface. When it comes to tile problems in swimming pools the most common is to have a failure of an entire section from bond sheer as described above. Almost every other failure of tile in a swimming pool will be from poor installation practices. When installed properly, tile in a pool can and should last up to and over 20 years or more. Some tile installations can even last twice this long.
Delaminating Tiles - Delaminating tiles are easy to locate. Simply draw a hammer, or screwdriver, or something heavy over the tiles and listen for the ones that sound distinctly hollow. Tiles can delaminate for a number of reasons such as deck sheer, failure of the mastic joint, failure of the grout allowing water to access behind the tiles, and failure of the substrate the tiles are installed over. If you remove the delaminated section of tile you can apply new tiles so long as you have a strong substrate to attach to.
Cracked Tiles - Tiles in concrete pools can crack from deck sheer forces, ice formation, efflorescence growth or physical impact. Since the tiles are attached to the substrate concrete with a ultra sticky thin set mortar, if the substrate cracks then the tiles are going to also crack (or pop off).
When you fix tiles in a concrete pool you should remove all of the old thin set to expose concrete that you can attach to. There are a lot of short cuts that can be taken when installing, repairing or renovating pool tiles. If you would like more information on this then you can read this article about how to install pool tiles.
Concrete Pool Surface Problems
The interior surface of a concrete pool is the most expensive maintenance item for your pool. Much like how a vinyl liner in a liner pool needs to be replaced, so must you renovate the interior surface of a concrete pool. Unlike a liner it is not always so easy to know when it is time to renovate the interior surface of a concrete pool. Part of the problem is that there are so many different kinds of pool surfaces and finishes it can be tough to get a straight answer. Where once sand and cement mortar (plaster) was troweled into place in every pool, you now have many different interior surface options ranging from pebble finishes to fiberglass finishes to roll-on finishes to interior surfaces finished with fire! Regardless of what style you have for your pool the same rules apply...once the finish loses the ability to (mostly) retain water, then it needs to be replaced.
How To Know When It's Time To Replaster Your Pool - Pool plaster is meant to be smooth, and the hallmark of a well done plaster is one that is so smooth it feels just as smooth as wet vinyl. When plaster ages the cement part of the mortar will wear away and leave only the sand behind. As a concrete pool plaster fails it will become more and more rough. As a real-world comparison, a decent pool plaster should feel like 800 to 1000 grit sandpaper at minimum. At 200 grit in feeling this would be the roughest you should let your plaster get. If your plaster feels like 100 grit sandpaper then you are well past the point of needing a new plaster layer as most of the water resistance in the smooth finish has been lost. Similar to re-installing tiles, you do not want to install a new interior surface over an older, failing one as the new layer will only be as strong as the layer it is installed over. Another general rule is that you can usually have two layers of interior surface installed before you need to strip both away and start fresh again with the third application.
With other interior surfaces such as pebbles, paint or any one of the many proprietary finishes, the finish is never smooth so it is much more difficult to determine exactly when you should resurface. The general rule of thumb you should adopt for resurfacing pools like this is to resurface any time you find that the surface is failing. This includes major cracking, delaminating, chalky residue or anything else that was not originally part of the interior surface finish. The average service life for an pool interior surface is between five to fifteen years, with seven to ten years being the average. If that sounds short to you, it is, but the pool industry no longer uses asbestos in plaster mixes. Asbestos infused plaster will outlast other pool plaster finishes by more than double, so always be wary when working on a pool with a very old plaster in unusually good condition.
There are a lot of options other than plaster for the interior surface of a concrete pool. One of the oldest alternative interior surface options is painting concrete pools. If you are interested to see the painting process you can read this article that highlights one method for how to paint a concrete pool. Before you start gearing up to paint your pool you might want to first read through this article that breaks down the cost comparison of pool plaster versus pool paint over a reasonable amount of time in order to make a true apples to apples comparison. This is a great read for concrete pool owners: pool plaster versus paint.
Concrete Pool Plumbing Problems
While swimming pool filtration systems are the same from one type of pool to the next, the part that is unique is how these pipes all terminate at the pool shell. In a vinyl pool you would attach pipes to the wall sections with flange assemblies that screw onto either side of the wall. With a concrete pool the pipes are simply installed where they are supposed to go, and left specifically long such that they will get cut off flush after the concrete is installed. This pipe penetration all the way through the structural shell opens the door for the possibility of a leak along the pipe. This water leaking effect can be stopped with something called a "pipe chase". You can install a pipe chase product along with the plumbing, or more commonly you can install a mastic bead where the pipe penetrates the inside of the wall of the pool.
Another common area of concern for concrete pool plumbing is the hydrostatic relief valve inside the main drain in the floor of the deep end. The hydrostatic relief valve is a mechanical spring and designed to allow water into the pool to stabilize the shell with any water that is surrounding the pool. This is used to prevent the pool shell from lifting out of the ground during periods of high ground water around the pool (or lowered levels of water in the pool). In older concrete pools these HRV's can become corroded or seized and should be replaced when performing resurfacing of the pool.
A concrete pool skimmer is an expensive place to develop a leak in a concrete pool. Most concrete pools will encase the entire skimmer in a box of concrete such that it is permanently anchored to the pool wall. This makes sure that the skimmer and pool wall will both move at the same time. Unfortunately if a leak develops in the joint where the plumbing connects to the underside of the skimmer this can turn into an expensive repair. If the concrete box needs to be jack hammered this will often damage the skimmer which would then require total replacement. For a walkthrough of this process you can read this article on how to replace a skimmer on a concrete pool.
How To Avoid Problems With A Concrete Pool
Despite the concrete pool problems discussed on this page, concrete pools are still the highest quality residential swimming pool option available in most areas. As with most things, if you own one, and take care of it properly, you can avoid the vast majority of problems that can develop. Of everything that you need to potentially do to your pool to make it last, probably the single most important thing you can do is monitor for unexplained water loss. Concrete pools quite often develop leaks slowly as part of a leeching process. When the pool interior becomes rough, and ages, it will begin to allow too much water to absorb into it. This would be evidenced with a slight increase in the rate of water loss in the pool.
Since many concrete pools also have automatic water fill valves it is important to periodically turn the fill line off and make sure that the rate of water loss has not increased. In order to test the rate of water loss, or if you suspect you have a leak, then you should read this thorough article on pool leak detection which will help you to understand the difficult nature of diagnosing and locating swimming pool leaks. You might also like to read one of the following articles:
Pool chemistry crash course
New pool owners fast facts
How to make you pool last as long as possible
8 Part series on how to inspect a concrete pool
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