I became inspired to do a little science project on pool plaster and a plaster alternative based off of experience, experimentation and frequent unsatisfied forum posts mentioning plaster discolorations, mottling, and roughness. In full disclosure, I will admit I am not terribly pleased with how my pebble surface looks and feels; this is probably the biggest driving factor in me looking for solutions to plaster issues.
Pool plaster has been around for a long time and has remained relatively unchanged. Recent trends are to replace or supplement marble dust (marcite) by adding pebbles, quartz fragments, glass beads, and colored pigments to alter the look and feel of the surface. While these additions have greatly changed the look and feel of the surface, they have also created undesired side effects. For example, pebble finishes frequently get complaints of a rough uneven texture, quartz finishes are prone to mottling, and colored plasters in general, discolor and/or lose their color completely.
A new(ish) product called Aquabright (http://www.ecopoolfinish.com) is a plaster alternative that instead of cement, uses a form of thermoplastic to act as the pool surface. I came across this product while searching for plaster issues and alternatives. There is little talk of this product on the forum and my curiosity got the best of me. I obtained several samples of this product and placed them through the same testing as the plaster samples.
Here is an example of one of the Aquabright samples:
Here is Mediterranean Blue Aquabright installed in a pool. The finish was about 2 years old. The pool almost looked odd because the color was so even and consistent... Nothing like I'm used to seeing.
Four sets of plaster samples were made (with a popular brand of plaster that will not be named) that represent common mixtures and curing practices used by applicators.
1.) .5 water cement ratio
2.) .5 water/cement ratio/ black pigment
3.) 1:1 water cement ratio/ 5% cacium chloride added
4.) 1:1 water cement ratio/ 5% cacium chloride added/ black pigment added
Here are the plaster samples:
They were poured onto a piece of tile so that they could later be cut and removed. The top side was troweled smooth and numbered, the underside is what will be shown in most of the photos/videos. Air bubbles created small voids on the underside of the samples but that should not influence their performance.
Each sample went through a slightly different curing process to represent industry practices:
These samples were submerged 1 hour after the last necessary troweling:
Within just a short period of time, the water clouded up from plaster dust. This is a common practice used by plasterers to get the pool filled as quickly as possible to prevent the plaster from drying out and cracking from shrinkage.
Here samples we left to dry for 6 hours before being submerged:
Just waiting a few extra hours nearly eliminated most of the plaster dust from forming. Although the plaster in the deep end will have sufficient time to cure and reduce dust, the problem is the shallower portions of the pool will not see water until 24 (or more) hours later. This can be especially problematic where the pool gets direct sunlight and on very warm days.
The bottom sample had no calcium added to the plaster and had < .5 water/cement ratio. The top 3 samples were the same mix but with (left) 1:1 water cement ratio, (middle) 5% calcium added, (right) 1;1 water/cement and calcium added. The variations in color are very apparent.
Plasterers add calcium as an accelerator to speed the curing process of the plaster. This allows for a surface to be quickly applied and troweled to a finish with minimal downtime so that multiple pools can be done in a single day. Excess water is added to the mix either out of lack of knowledge or easier workability. Neither are desirable for longevity or aesthetics of the pool surface.
These samples were cured in the exact same manner, the bottom sample had 5% calcium added.
For the first experiment, the cured samples were placed into a container of full strength muriatic acid
Video - Acid Exposure
Here are the samples after being exposed to acid:
And what remained in the container:
The remaining yellow color is from the impurities in the acid and can be disregarded. Many of the pebbles became dislodged as the cementious plaster dissolved that was originally holding them in place.
A well maintained pool surface should never be exposed to straight acid but if stains, discolorations, and scale occur, they are typically resolved by acid washing the surface. In this process, significant damage is done to the plaster making the surface rough and porous leading to increased surface area. A larger surface area is weaker and allows more area to be exposed to potential stains and organics. Stains and algae will be more difficult to remove if they make their way into the porous areas of the surface where brushing may not be able to reach. Additionally, careless acid additions have the possibility to create clouds of very low pH that can sink and remain near the floor of the pool since hydrochloric acid has a specific gravity greater than that of water (sinks in water). This is why it is recommended to lightly brush the pool surface after adding any chemicals (especially acid and chlorine).
A set of examples was partially exposed to pure chlorine (trade – 12.5%) as seen here:
The results after being exposed to the chlorine for 48 hours:
Blue pigments are notorious for losing their color because the pigments themselves are made from organic sources. Chlorine is used to kill organics, so it isn’t difficult to understand why the blue color will fade with time while exposed to chlorine. There was a recent post where a new type of blue pigment was developed that was not derived from organics and may prove to be the solution to this issue.
I chose to use a black pigment for these samples since black is an inorganic pigment and being a darker color, is subject to mottling and discolorations. I did not have any blue plaster available for this little experiment but if I can get ahold of some, I will do the same exposure to it and add the results to this thread.
Here is midnight blue minipebble plaster that is 1-1/2 years old. If you look closely, you can see that the plaster between the pebbles has completely lost its color:
A 5 gallon water sample was made with a pH of <4, TA = 0, and a FC level of 1,000 ppm. These samples were cured for 1 week and then submerged for 48 hours.
Here is the water sample:
And here are the results:
A 5 gallon water sample was made with a CH >1000 ppm, TA > 1,000 ppm and fertilizer added to promote algae growth. Here is the sample:
Here are the results after 48 hours (admittedly I had hoped for much more algae):
The samples were returned to the aggressive and the oversaturated water. They will be allowed to sit for another week to see if there are any further changes.
At this point, it looks like Aquabright may be a viable plaster alternative. I wouldn’t say that its better than plaster in every way but it could be at least viewed as another option for a pool surface. It has certainly held up well to pretty harsh environments and provides a smooth uniform finish.
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Updated Testing - 1 Week Later - 8/27/16
Here is the oversaturated bucket (1,000 ppm CH, 1,000 ppm TA). Only slight algae was visible:
I used the samples that were in the bucket with pH <4, TA =0, and chlorine at 1,000 ppm for the following video. Its easy to see that the plaster samples suffered some serious damage. The Aquabright sample looked the same as it did before going into the water.
Scratch test can be seen here:
Here is a close up of the scratched sample:
Since Aquabright gets installed with heat, I took a heat gun to the scratched sample for about 2-3 minutes:
The plaster samples had deep scratches. The only way to repair these would be to chip of out the area and replaster. The chances of an unnoticeable match are slim. With the Aquabright sample, the high heat nearly liquified the surface and sealed the scratch. While the scratch is still slightly visible, had I used the actual applicator gun, the scratch would be completely gone.
The following is a video to show the flexibility of the finish:
I'm impressed, so much so that I am in the process of becoming a certified installer.