Replastering is the process of adding a new layer of mortar over the entire interior surface of a concrete pool that already has an existing layer of plaster. This is a maintenance item, and one of the more expensive and common ones that you will need to do if you own a concrete swimming pool. On average every five to ten years you will need to replaster your swimming pool. The age itself is not what dictates when you need a new plaster job, but instead the roughness of the finish is how you tell when it is time to replaster.
Much like putting shingles on a roof, the first time that you need to re-apply (shingles or pool plaster) you can simply add them overtop of the original application. However, much like shingles, you can not simply continue to add layer after layer. The industry wide accepted practice is to only add a total of two layers of pool plaster. If you already have two layers you should not add a third, but instead remove the original two layers and start fresh from the concrete shell. This approach will help to ensure that your new pool plaster stays where you put it.
If you add new pool plaster overtop of old, delaminated pool plaster, then the new layer is no better than the old. Even if you have a well adhered base layer on your plaster, there is a concern for the thickness of the plaster buildup. Each layer of plaster will be on average between 1/2" and 3/4" thick. By the third plaster application there would be significant visual detraction from the quality of the job.
Coping, Tile & Plaster - Coping, tile and plaster go hand in hand in the world of concrete pools. Fortunately tile bands and coping stones tend to last longer than the plastered interior surface of the pool. Instead of every five to ten years like replastering, coping and tile will last at minimum twice as long, with quality installations being able to last decades in intact condition. While it is possible to make repairs to coping and tile without also doing the plaster, this can lead to sub-par quality workmanship due to the difficulties of working around a water filled pool. If you are going to need tile and coping repairs or replacement you should absolutely do these in the same project as your replastering. The chronological order for these items works from the top down in a swimming pool. If everything needs to be replaced, you demo everything at the same time and then install first the coping, then the mud base and tile, and then plaster the interior surface of the pool immediately before filling with water and starting the system.
How To Replaster A Pool
Replastering a pool is something that can't be done unless you have experience specifically with this process. If you are looking for information on how to plaster a pool yourself then you need to understand a few things. First, troweling an entire pool plaster without the help of at least a few skilled plaster masons is just silly. Not is it just a bad idea, but you literally have no chance of having it turn out acceptably. Unless you finish concrete for a living, there is no way that a pool owner should ever try to plaster their own pool and fortunately they don't need to. There are alternatives these days such as various forms of paint as well as newer roll on plaster applications. While the alternatives might be attractive to those not able to plaster a pool, my professional experience is that plaster is superior to all forms of paint and roll on interior surface coatings.
Plaster Versus Paint In Concrete Pools - The discussion of pool plaster versus paint is decades old in the pool industry. Time and again pool owners turn to paint as a somewhat viable option and alternative to replastering their pool. There are various kinds of paints available, and some of them will last quite a while when applied properly, but at the end of the day there is a reason why almost all concrete pool industry professionals agree that plaster is better than paint. If you are interested to know more about why plaster is considered better than paint once you consider the whole service life of the pool, you should read this article that breaks down the costs involved in owning a painted concrete pool for 25 years versus a plastered concrete pool for 25 years: pool plaster versus paint.
The very first step involved with replastering a pool is to simply inspect the pool to see what you are dealing with. This includes inspecting the tile and coping for any deficiencies that must be attended to. If there are small imperfections that account for less than 10% of the overall linear footage of the coping or tile then these should be repaired prior to replastering the pool.
If more than 10% of the coping is broken or delaminated then the entire coping system should be removed and replaced. The same can be said for the tile in that if more than 10% of it has cracked, broken or fallen off then all of the tile should be stripped and the old thin set chipped out down to the base shell concrete. If the coping and tile band both pass your inspection then you can proceed to replastering the pool.
Removing Old Pool Plaster
Even if this is only your second pool plaster and you are not removing the original layer completely, you still need to remove (chip out with a small jack hammer / chipping hammer) plaster in some key strategic areas. For example, right now your pool plaster and your tile band meet flush, or at least they should. If you add a new layer of 1/2" to 3/4" plaster then you will have a bulge where the tile and plaster meet. The other option to feather out the plaster thin at the top is a bad idea as this will make the new plaster very weak in this spot. You for sure want to apply the new plaster at 1/2" to 3/4" everywhere evenly. This is why you need to chip out some old plaster. Usually you would take out about eight inches to twelve inches of plaster directly below the tile band. So as to make sure the tiles are not disturbed during this process you would usually make a clean cut with a diamond cutting blade with a grinder immediately below the bottom tile.
By chipping out this plaster below the tile band you can marry the edge of the new plaster to be perfectly flush with the existing tiles. You can also avoid a bulge in the plaster by using the full width of the chipped-out area to blend the two elevations seamlessly together. This is the same process that you should do around all terminations in the plaster such as each return fitting, main drain, or any other protrusion in the pool that you want the new plaster to marry flush with on the edges. When done properly the end result would appear to be "as good as new" in that only a skilled eye will be able to notice that the pool has actually been replastered.
Delaminated Pool Plaster
Once the pool is drained you can begin inspecting the interior surface more closely. The first thing that you would do during this thorough inspection would be to pass over the entire interior surface of the pool with a hammer or stone (or something heavy) so that you can identify all areas of the old plaster which have become delaminated from the base shell surface. Simply carry a construction pencil around with you and circle all of the areas which you are able to find that sound hollow. You will need to chip all of these areas out in addition to the areas below the tile band and around return and main drain fittings. Generally speaking if anything more than 10% to 20% of the pool plaster has delaminated you should consider chipping out the entire interior surface. It is a lot of work now, but is the only way to ensure that you are not back in the exact same position in only a few years time.
Usually you would not need to fill these chipped out areas with plaster ahead of time. A small deviation in thickness of the new plaster will only minimally affect the application and hard trowel of the new surface. Once you have finished all work to the tile and coping band, and you have removed all of the loose plaster in the pool, as well as chipping under the tile band and around all existing fittings, you can begin to prepare the pool for replastering.
Preparation For Pool Plaster
There is a lot of work to do to get your pool ready for replastering. At this stage you need to work on cleaning the pool out from top to bottom. This usually would start by setting up a smaller submersible pump that will run throughout the process. Next you would simply take a (high powered) garden hose, or (low powered) pressure washer and rinse the entire pool from top down to the bottom. This process is less for making the surface look cleaner, and more for making sure that all sand, gravel and loose debris has been swept or vacuumed up by the end of the preparation.
Acid Washing - The reason why you do not need to worry about pressure washing the heck out of the existing surface of the pool is simply because the next step is acid washing it, which does a very thorough job of cleaning the surface. After washing the pool mix one part muriatic acid into seven parts water in a plastic watering can (like you would use in your garden) and apply this to the pool from the top down. You do not need to worry about the streaks that develop since your only goal is to clean the surface so the new plaster will adhere properly. While acid washing the pool the submersible pump should be removed, and pooling water in the bottom should be treated with baking soda to neutralize the pH before pumping away.
After acid washing the pool it is important to rinse the entire pool down multiple times to help neutralize the acidity of the concrete. If any areas of the existing plaster are still green, these should be dealt with before applying a new plaster layer. Organic matter trapped between the plaster layers will almost certainly cause a premature delamination of the new layer. Spot treat any green areas on the old plaster with a pressure washer to help remove them. The only other matter you need to prepare for your plaster is to locate 8,000 to 12,000 lbs of bagged sand and white portland cement onto your pool deck - no sweat!
Is It Hard To Plaster A Pool?
Look, applying a thin layer of mortar to the inside of a pool is not rocket science...but that being said there are a ton of ways that you can make a mess of it if you tried to do it yourself. A pool plaster, when left to the professionals, would be a six hour job or so for an average sized residential swimming pool. The trick is both in knowing how (and when) to work the mortar, but also in having the physical ability to finish flat on a curved surface. It is much, much harder than it sounds, and it needs to be done all in one shot. Pool plaster needs to be applied uniformly throughout the entire pool.
Timing is everything when it comes to plastering a pool. The slurry mix needs to be applied to damp, not wet, base concrete. The slurry coat then needs a minute to set up (but NOT dry) and then you apply the first layer of plaster with the edge of the trowel. This serves to mechanically press the new plaster into the old surface, and the second pass with the trowel (which happens right away) brings more material with it and should get the plaster to within 80% smooth, flat and flush.
Once the first pass has been completed you should have a pool that looks 80% replastered. The second pass happens once the mortar has had a short while to stiffen up. You do not want it to be hard yet, but you want the glistening wet appearance of the surface to be more of a hazy / dry appearance. During the second pass you will be walking on spiked shoes or knee boards, and you will get the pool from 80% smooth finished as close to 100% as you can get. Everywhere you go in the pool you will need to fill and fix the tiny holes from your spikes so efficient work is important. The final pass happens when the pool plaster is almost completely hard. Using a spray bottle with water, as well as a sponge float, you continue to smooth out the surface, as well as apply an on-edge trowel (hard trowel) which should leave the surface of the pool as smooth as the paint on a new car. The rougher the finish is, the lower the quality of the plaster work.
Filling The Pool After New Plaster - After you plaster a pool you are supposed to wait until the plaster is "hard" before filling which is usually a minimum of 24 hours or so, depending on ambient temperature and amount of calcium in the plaster mix. Essentially, you want to fill the pool as soon as it is hard enough to not be damaged by the water. The water will actually help to hydrate the plaster, which ensures a stronger finish with minimal hairline cracking, as well as protecting the plaster from staining. Fresh white pool plaster can be stained easily by organic debris that might blow into the pool so protecting with a tarp would be a good idea until the surface has cured enough to start filling. Once you start filling a newly plastered pool with water it is CRITICAL that you do not turn off the hose until the water level reaches the tile band. If the water level stops rising for even a short period, the fresh plaster will form a near-permanent scum line where the water level stopped. You should also add a metal remover and stain preventer as you fill the pool, such as a sequestering agent to prevent contaminants in the fill water from causing staining in the pool. Close care should be given to the calcium hardness and pH levels for the first 30 days after filling the pool.
If you have a concrete pool and you are researching replastering then you might find some of the following articles and resources to be useful. Owning a concrete pool is a luxury, but they can also be very expensive and unforgiving if you do not maintain and repair them properly.
Pool Plaster VS. Paint Cost Comparison
How To Fix Pool Tiles
How To Paint A Concrete Pool
Important Concrete Pool Maintenance Items
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