Swimming Pool Plaster Repairs
Concrete swimming pools are the best pools that money can buy but when it comes to repairs, like to the interior surface of the pool, the repair costs can get very heavy, very quickly. The interior surface of a concrete pool is a very dense mortar that is troweled to a water resistant smooth finish. The base layer, or structure of a concrete pool, is made from concrete and steel reinforcing. Concrete however is porous which means that water would leak out constantly. In order to limit this problem, a very dense mortar layer, called plaster, is applied over the entire interior surface of the pool. The plaster layer is a very dense mortar, which reduces water permeability, however troweling the plaster when it is nearly already hard, called a "hard trowel" is where the majority of the water resistance comes from.
It is important to note that all concrete pools "leak" water. Concrete is porous, even plaster, and as such a small amount of water will always leach through the interior surface - this is normal for concrete swimming pools
There is no such thing as a waterproof concrete pool - only varying degrees of water resistance. The only potential "waterproof" concrete pool would be one that has an interior surface entirely comprised of Laticrete backed tile which is a cementitious layer engineered to be fully water proof. Almost no residential concrete pools are all tile, and of the few that are all tile, very few (almost none) were installed using the Laticrete system. What does all this mean to you as a pool owner? It is important to understand some truths about how concrete pools work, how they leak, and what realistically you can do about it. If you have a concrete pool with an older or failing interior surface (plaster) then the information on this page will help you to understand what the concerns are, and what kind of repairs you can do on your own to limit or potentially eliminate the problem.
Swimming Pool Resurfacing
Concrete swimming pools will periodically require renovation or resurfacing. Since a concrete pool is made from concrete and mortar (a cement product) this means that
concrete pools are NOT 100% waterproof. What they are is very water resistant. Concrete pools are typically buried in the ground but if you could see the backside of
the walls on your pool you would see extensive efflorescence staining. Efflorescence is a white crystal growth that appears in any areas where there is water migrating
through the concrete. You may have seen something like this before if you have tiles in your pool, or if you have a concrete or natural stone coping. The reason the
backside of the walls in your concrete pool would be covered in efflorescence is because there has been water actively migrating through the walls. As the efflorescence
forms, the crystal growth will eventually block the path the water is taking which will stop the leak in this location. This is the life cycle of a concrete pool.
It is important to understand the difference between an active leak, and the leaching effect that concrete pools experience. If you were to be able to see the back of your pool walls, you would not see water actively dripping or leaking out. What you would experience is that the concrete shell would be damp (saturated) with water. As a concrete pool ages, the interior surface of the pool becomes rough to the touch. This roughness is a result of the mortar layer (plaster) failing. As the mortar ages, the cement component will be washed away with the slow movement of water. The sand component of the mortar will not be as soluble, and will be left behind. In the absence of the smooth mortar layer surface, the water resistance of the plaster will drop steadily. Where once your pool would leach water very slowly, the interior surface of the pool will eventually be so porous as to provide no benefit to water resistance. At this point the water in the pool will absorb readily into the shell structure.
You may even be inclined to think that you have a specific leak in your pool such as a broken pipe or structural crack, but in reality it is the cumulative effect of the reduced water resistance of the plaster over the entire surface area of your pool.
The problem with pool plastering (marbelite, marcite, quartzite, plaster, as well as about 100 proprietary names) is that it is really is not a do-it-yourself level of project. To plaster a pool correctly you would need the ability to plaster the entire surface area, including letting the plaster set up before hard troweling, all within about 6 hours. This would normally take 2 - 4 very skilled plaster finishers. 20 unskilled plaster finishers will not be able to do the job that even 2 skilled plasterers could do so you do not have the option of just bringing in extra unskilled labor to get the job done. Unless you have exceptional troweling, concrete and construction skills and resources you will not have the option to resurface your swimming pool on your own. This is the reason that so many concrete pool owners end up choosing paint for the interior surface of their pool.
While paint is inferior to plaster in every way, and using paint on your pool can often lead to extra expenses down the road like needing to sand blast, many pool owners choose paint simply because they can potentially apply it themselves. All things being equal, pool plaster is a much better path than painting your pool and I would always encourage concrete pool owners to consider plaster as opposed to paint as over the course of 25 years the plaster will be about the same amount of money, less work, plus a higher end feel and finish. Pool paint, while cheaper upfront than a single pool resurfacing with plaster, does not last as long and will require far more maintenance and resurfacing over the years than new plaster will. Still, if your situation requires that you need the lowest cost possible interior surface for your pool, and you need to be able to do it yourself, then you should read this article I wrote that details which paint you should use if you plan to paint your own pool for cheap.
How To Fix Pool Plaster
Now that you have a better understanding to how pool plaster works, how it fails, and how it differs from painted interior surfaces, we can start to look at how you
can perform repairs to your pool plaster. While resurfacing your entire pool with plaster may not be a DIY level project, you certainly will be able to make repairs
to cracks, holes and delaminated areas with a little instruction. In order to understand what kind of repairs you should be able to do we should first look at the
different ways that pool plaster can fail:
Crazing - Crazing is a network of spider cracks that appear in concrete due to the contraction of the surface layer as the concrete cures. Since concrete shrinks as it cures the development of crazing will set in shortly after new concrete has been finished. This typically would appear within one to three days after a new plaster resurfacing. Most commonly the crazing will not be visible, or be only minimally visible when wet or underwater. Crazing will be most apparent when the pool surface is dry and you spray it with water. The miniscule cracks from the crazing will have a dark contrast when compared to the rest of the plaster layer. Crazing usually does not actively leak water although it will incrementally increase the rate at which your interior surface leaches water to the substrate layer. Since crazing cracks are so shallow they can almost not be detected by feel and are not something that you can patch over in your pool. To minimize crazing when resurfacing a concrete pool you want to apply the new layer well before any direct sunlight or heat touches the plaster. A 6 hour plaster project often would be started around 5 or 6 in the morning. This way by the time the heat of the day and the direct sunlight are on the pool, the plaster has been finished.
Non structural cracks - A non structural crack in a concrete pool refers to a crack in the interior surface layer (plaster) and not through the concrete shell. There are many reasons that a crack might develop in your plaster layer however most of these would be from the initial placement of the plaster. Cracks that develop later in the life of the plaster are most likely to be due to a crack in the shell layer to which the plaster is bonded. A non structural crack in pool plaster that develops later in the life of the plaster will almost certainly be a result of a delaminated area of plaster. This could be from poor bonding of the plaster layer in the pool which allow pool water to access a pocket in between the shell and the plaster.
Structural cracks - A structural crack in a concrete pool will present itself in mostly the same way as a non structural crack. For you, the pool owner, both look the same in that all you can see is a crack in the interior surface of the pool. There are a few different ways to differentiate between structural cracks and non-structural cracks in a concrete pool. The first is simply the location, length and depth of the crack. I would expect a non-structural crack to be smaller, narrower, shallower and shorter than a structural crack. Any crack that runs for more than a linear foot or two is highly suspect of being a structural crack. Typical symptoms of structural cracks might be crack that runs the width or length of the pool in any orientation, floor or walls, as well as any crack that segments an entire section of the pool such as a crack from the main drain to each of the deep end corners in the pool. Aside from visually inspecting the cracked areas to see if the crack continues past the plaster layer and into the shell, you can also try dye testing the crack to see if it is actively pulling water. If you need more information on how to dye test you can find this information in this pool leak detection article. If it is determined that you have a structural crack in your pool this is a very bad situation to have. Patching and new plaster will not stop a structural crack from leaking, or getting worse, unless the crack is no longer migrating. There are some rare cases where a pool will settle, perhaps due to a one time environmental event such as a leak or flood, and it will crack structurally but cease movement after cracking. If you have a crack that is completely stationary then you may be able to fix the leak with an injectable urethane followed by a water stop concrete patch.
Delaminating - Since plaster is only around half an inch thick it is not very strong on its own. When applied over the concrete shell of the pool it must be bonded. Bonding concrete involves removing all grease, oil and dust from the shell, and applying a bonding slurry over the concrete shell, and then plastering over this bonding layer. There are a number of things that can go wrong with this process that can result in the plaster delaminating, either right away, or within a few years. If the existing concrete layer is dirty, greasy or has any physical debris then this will certainly prevent a strong bond between the plaster and the shell. If the shell concrete is too dry when plastered this can also cause a delamination between the layers. If the bonding layer itself is allowed to dry too much before the plaster is applied over it then this could also cause a delamination. Finding delaminated plaster in a concrete pool is actually very easy with the only exception being that the pool needs to be emptied. Dragging any heavy tool such as a hammer, or heavy screwdriver handle over the pool plaster will reveal any delaminated areas. Any areas that are delaminated will sound very hollow, so much so that you would be hard pressed to not be able to tell the difference. Any plaster areas that sound hollow have already delaminated and will likely continue to crack and get worse unless you remove them and patch these areas.
How To Prepare Your Pool For Patching
Now that you understand more about the different ways that the plaster layer in your pool can fail we can begin to look at some of the repair options available to you. Crazing is not something that needs to be patched, and structural cracking requires a much more extensive remediation process than simply patching the plaster. This means you should only attempt to patch non-structural cracks and delaminated areas of the plaster.
Draining a concrete swimming pool has risk and in order to safely drain it you should control the ground water surrounding the pool with a sump well as well as removing the hydrostatic relief valve from the pool for the duration of the time the pool is empty. You should never drain a concrete pool during periods of high water tables such as during heavy rains or spring melts.
Once your pool has been emptied (being sure to remove the hydrostatic relief valve from the main drain, as well as controlling the ground water table surrounding your pool) you can begin the process of identifying all of the problem areas. Use a thick carpenters pencil to outline any area of the pool that needs repairs. Looking at white plaster in direct sunlight can be hard on the eyes and outlining with pencil is a great way to make sure you don't miss any areas. Drag a hammer, or heavy screwdriver, over the entire surface of your pool. Be sure that the tool you choose is not leaving any marks on the plaster, and if it is try choosing another tool for this process. Every time you find a delaminated area, use your dragging tool and pencil to find and mark the entire delaminated section. When you remove these areas you want to completely remove any delaminated spots. If you leave any small delaminated spots the problem is likely to grow and return. If you can manage to remove all of the delaminated plaster areas and then bond / patch it, this should resolve any potential for leaks or further damage in this area.
NOTE - A normal amount of delaminated area to encounter might be around 10% of the total pool surface area at absolute most. If you have extensive delamination, more than just some small sections in your pool, then this indicates a systemic failure of the bonding layer. Patching of a pool in this condition would not be advisable as you are very likely to experienced continued failure. This would be either a result of poor installation or potentially the plaster layer in your pool reaching the end of its service life. If you have more than 10% delamination of your pool interior surface then the correct remediation would involve sand blasting the pool down to the substrate concrete shell before resurfacing with a new plaster layer.
Once you have found and outlined all of the cracks and delaminated areas in the pool you can begin the process of removing them. Delaminated areas are best to be removed with a hammer, a sledge hammer, or a chipping hammer (small jackhammer). Since the plaster has delaminated it will be very weak in these areas. You do not need to hit it hard, nor do you want to hit it hard, as you do not want to do anything more than chip away the plaster in these delaminated areas. Once you have tapped a hole through the plaster in the middle of the delamination, the rest of the delaminated plaster will chip away easily. Start from the center of the failed area and work your way towards the edges until you encounter plaster that is not delaminated. Delaminated plaster will break off easily in big chunks. When the plaster is bonded properly it will only break off in tiny pieces, or even dust.
Preparing non-structural cracks for patching is a little different than with delaminated plaster. You do not want to hit cracks with a hammer as you will cause a larger problem with the plaster area around the crack. Instead you want to use an angle grinder along with a masonry blade to cut the cracked areas out. Once you cut on both sides of the crack you can chip out the cracked area. You can use the angle grinder to cut out any loose debris however you should be aware that cutting masonry with a hand held angle grinder is not for the feint of heart. Angle grinders are very powerful, very loud and very dangerous. If you are afraid of using a tool, this drastically increases the chances you will have an accident using it. If you are not extremely comfortable with the safe operation of an angle grinder then you should not attempt to do these repairs on your own.
By the book, once you have chipped away the delaminated plaster and cut out any cracks, you need to prepare the surface for patching. This involves using muriatic acid and water mixed in a plastic garden sprinkling can with approximately 1 part of acid to 7-10 parts of water. Start by using a garden hose to rinse out the cracks and delaminated areas. Next pour the mixed acid onto these areas. You should see a very small amount of fizzing if you have a decent mix ratio of your acid to water. Let the acid work for about 60 seconds and then rinse thoroughly with a garden hose. At this point many pool workers might proceed to patching however there is an additional step of using a TSP rinse of the area that is recommended. Sometimes the acid can leave the pH of the concrete too acidic to patch effectively. By using a TSP rinse you will neutralize the acid wash. Again, be sure to rinse with a garden hose thoroughly after TSP rinsing.
How To Patch Pool Plaster
Now the delaminated areas and cracks are ready to patch. You will want to remove any standing water from these areas using a wet/dry shop vacuum. You want the
patched areas to be slightly damp, but not wet. You will need to use a bonding layer, which you can read about in this article about how to
work with concrete. If you are bonding plaster then you would want to use white Portland cement in place of regular grey Portland cement when making your bonding
slurry. The grey would work just fine however most pool plaster is white and you want to color match your patch materials for optimal results. Once you have applied
the bonding slurry you can now apply your plaster mix into these areas. A standard pool plaster mix is made from 1 part Federal white Portland cement, mixed with 2
parts fine graded white silica sand. You can also add a small amount of the Weldbond concrete adhesive that you used in the bonding slurry directly to your plaster mix for maximum bonding ability. When you mix your plaster materials together you want to
avoid adding too much water. Adding too much water is the most common mistake that pool owners will make when mixing patches for their pool plaster. Concrete
actually needs very little water to actuate properly. You want to achieve a consistency slightly more wet than damp sand, but slightly less watery than smooth peanut
butter. Apply the patch over the cracks and delaminated areas and use a pool trowel to
flatten the area.
A novice concrete worker will also make the mistake of over-troweling the concrete. When you first apply the patch you want to smooth the area, but only as much as you can get in two or three passes. Even if the patch is still not smooth and level you want to stop at this stage and wait for the concrete to start to set up before finishing further. Troweling the patch too much will raise too much water and will cause the surface to become very weak and the patch to dry out and crack. To avoid this, apply your patch, trowel for only a few moments, and then let it sit until you can feel that it is beginning to become stiff. Once you can feel the patch mix starting to stiffen up this is the point you want to try to put the finishing touches on it. You would add a tiny amount of water with a spray bottle and then use a sponge float and work in a circular pattern. This will allow you to blend the elevations of the surface of the patch without disrupting the bond of the patch itself. The sponge float will help a lot to level the patch as well as marry the edges of your patch to the existing pool plaster. Once you have sponged it level, you can trowel again with your steel trowel. You should be able to apply a fair amount of force this time which will leave the patch with a smooth, sheen surface. Again, you must resist over troweling even at this stage. You get between two or three passes before you start to raise too much water and damage the integrity of the patch. If you can not get the patch perfect, you are better off to leave it and sand it the next day to the best of your ability. It will not look perfect but at least the patch will be working properly.
Once the patch has dried and is completely hard to the touch (between 2 - 12 hours depending on ambient temperatures) you want to refill the pool right away. Concrete is made weak with too much water when you mix it but as soon as the concrete becomes hard to the touch (actuated) then water begins to aid curing and ensure maximum hardened strength. Block patches from direct sunlight until they are hard to the touch and fill your pool as soon as possible after patching for optimal results.
How To Make Pool Patch
Assuming you can find the materials, mixing patch for your pool plaster is easy to do. The actual mix will vary from builder to builder however if you have a white or
off-white interior pool surface then you can patch it using the following mix proportions:
1 Part Federal White Portland Cement
2 Parts Fine Graded White Silica Sand
5% Liquid Volume Weldbond Adhesive (for every 1000ml of water you would use 50ml of adhesive)
The only problem with this is that you are very likely to have trouble sourcing these materials in your area. If you are able to find white Portland cement and fine white sand in your area then you can simply make your own pool patch and it is not very expensive at all. A 90 lb bag of white Portland is usually around $50 and white sand can be around $15 for a 80 - 100 lb bag. If you can find a specialty concrete materials supplier in your area this will be your best bet. For most people, you will probably find it is extremely hard to find these materials. If you can not find the base ingredients to make your plaster mix patch you could try speaking to local concrete pool companies. You may be able to negotiate to buy a few bags of material from them. Even if you pay a surcharge for this service, it will still be much cheaper than any other method of patching your plaster if you have to buy a premixed patch product.
For most concrete pool owners looking to patch delaminated areas and cracks in their pool plaster this will be the most convenient patch product you will find. If you can find the base ingredients as listed above to make your own pool plaster then I would go this route, but for everyone else this pre-mixed pool plaster patch will be your most readily available option. While the composition of the patch product, as well as the patch process, is slightly different than the application methods described above (dry application versus damp application), if you are looking to fix cracks and delaminated areas in your pool then this product will get the job done.
IMPORTANT NOTE - When you mix a dry plaster mix with water it will reduce in size drastically. Be sure to buy much more patch product than you think you will need. It does not go very far at all. You are much better to have too much than too little and need to wait with your pool empty for more to be delivered. If you buy extra and store it in climate controlled and dry location it will last for many years.
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