The Art of Good Pool Plaster Color

onBalance

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Jul 25, 2011
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An attractive plaster color (other than white) is often preferred by pool owners. However, it is very difficult for plasterers to produce a uniform and consistent color. The reality is that there will always be some minor shading (mottling) and variation in the color and can never be uniform looking like paint or fiberglass.

One of the primary reasons for non-uniformity is that pool plaster a hand-finished product. It is plastered by multiple finishers and subjected to a variable environment during curing. Most pools are also plastered using multiple batches of material which will never match precisely.

Pool owners need to accept that reality. In fact, the National Plasterers Council (NPC) appropriately recommends that a “Disclaimer or Waiver” be provided to pool owners to explain that there may be slight differences in the color shading.

Fortunately, quality-oriented plaster companies know how to produce a relatively good-looking color finish that will satisfy most pool owners. Along with other good practices, such as tenting pools to control temperature and humidity, they use colorfast pigments, a low and consistent water/cement ratio in all batches of material, they do not add any calcium chloride and do not add water to the surface during the troweling process. Lastly, they achieve a smooth finish with a properly-timed final troweling before the plaster becomes too stiff.

When the Color goes Bad

Obviously, poor chemical maintenance can either etch or scale any surface, including colored surfaces, but those are known and accepted phenomena. There are two non-chemical reasons for color problems developing with new plaster finishes, including quartz and pebble finishes. They are workmanship and materials.

When a pool is plastered too fast, due to adding too much calcium chloride set accelerant, the plaster surface can display severe and irregular mottling, color fading, or white blotchiness, streaking, and spotting. Also, if other quality workmanship practices, such as proper troweling, trowel pass timing, water/cement ratio, refraining from wet (water) troweling or propane torching, etc. are not followed, increased negative effects may plague the surface aesthetics. And understand that those ugly discoloration problems generally take a few months to worsen and become increasingly visible.

Of course, a “Disclaimer or Waiver” document should be not used as an excuse by plasterers to avoid taking responsibility for their work quality.

The above discoloration issues are not caused by aggressive water. If it did, then colored cement driveways and walls (on buildings) would have similar results when rained upon (which is aggressive water). Yet, they do not because they are usually applied properly.

On other hand, overly positive LSI (or CSI) pool water can cause calcium scaling and can mask the colored plaster with a whitish deposit. When that happens, acid (aggressive water) treatments are often performed to remove the white discoloration and darken the plaster color again. Also, many quartz and pebble companies recommend maintaining the pool water slightly aggressive to prevent the general whitening process from occurring altogether.

Therefore, aggressive water cannot be the cause when it removes the “white discoloration” and darkens the plaster color. And there are no plaster studies showing that slightly aggressive pool water causes irregular white blotchiness, splotches, or streaking in colored (or white) plaster pools to appear in just a few months.

Evidence from plaster/cement petrographic “forensics” studies show the cause and effect relationships between color surface failure and improper workmanship practices. See this link for reports on this topic. Consulting – Pool Help

The Bottom Line

Good workmanship standards are needed for the pool plastering trade.
See this link for information regarding proper plastering practices: Ten Guidelines for Quality Pool Plaster
 
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onBalance

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Yes, torching is generally detrimental to a plaster finish. Plaster/cement needs "water" to properly hydrate and harden. The drying or heating of a plaster surface can stop that process. It can cause expansion and may reverse the hydration process altogether. You can google the effects of hot temperatures of concrete/cement surfaces and read up on that.

As I understand it, even torching weeks later (after the pool has been filled with water and then drained) to remove graying problems can structurally damage plaster/cement surfaces by causing porosity and micro-cracking due to heat expansion.

Some plasterers pretend that nothing can go wrong with heat torching, and of course, the damage doesn't always show up immediately. The damage may take some time (months) to become visible after the pool is refilled which makes it easy to blame it on poor water balance instead of what originally caused the degradation or discoloration. And that is what happens often.
 
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ajw22

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Jul 21, 2013
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It appears the NPC or at least Eric disagrees on torching if done right and in right conditions.
https://cdn.ymaws.com/www.npconline.org/resource/resmgr/Technical_Library/TheEdgeQ116_Torching.pdf

You posted a picture of torching during plastering and @onBalance said why it is a poor practice.

The article you link to discusses a different use for torching - to address abnormal discoloration (often defined as “radical departure from the anticipated color.”)

I don’t think there is any disagreement. @onBalance mentioned the same risks of damage that the article warned of if not done correctly. With all of the issues in getting plaster applied correctly I don’t know why you would trust that they would know how to torch a pool properly.
 

CaveDiver1932

Well-known member
Mar 2, 2014
110
Dallas
Allen, I’m impartial.
@onBalance mentioned the same risks of damage that the article warned of if not done correctly. With all of the issues in getting plaster applied correctly I don’t know why you would trust that they would know how to torch a pool properly.
When did I say I trust... that crew/company is not some fly by night outfit. There is a high probability that this highly trained crew picked this process up from and traced back to the NPC.

Allen, you may not be aware, .. the OnBalance team and the NPC don’t agree on many issues. I like OnBalance and find it a shame that the NPC has chosen to ignore valid concerns brought up with those in the industry.
 
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ajw22

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Jul 21, 2013
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There is a high probability that this highly trained crew picked this process up from and traced back to the NPC.

I think that there is a low probability of finding and validating such a highly trained crew in a local area. Many crews will make claims that consumers have no way of verifying.

Allen, you may not be aware, .. the OnBalance team and the NPC don’t agree on many issues. I like OnBalance and find it a shame that the NPC has chosen to ignore valid concerns brought up with those in the industry.

I am well aware and appreciate the perspectives that @onBalance brings to us. I do not understand what you expect to accomplish by pointing out the conflicts with the NPC party lines. If someone from the NPC wants to join in the discussion I am sure they will be welcomed.
 

CaveDiver1932

Well-known member
Mar 2, 2014
110
Dallas
Allen, cause everyone has their own agenda...and that confuses the consumer.

I know a little bit about that crew...sooooo.. and I question the use of the torch... and no, that’s not one of my pools.
 

ajw22

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Jul 21, 2013
24,802
Northern NJ
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TFP is about simplicty, education, and science. @onblance suports his viewpoints sharing his tests and the science behind it. NPC may have their own motivations and should they come here then it may become a discussion topic. Until then I don’t think we need to rehash conflicts within the industry.
 

onBalance

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I find it unfortunate that an NPC representative suggests that torching plaster surfaces is an acceptable practice. There are a number of things in that torching article that are misleading or factually incorrect. It is false that soft or slightly aggressive fill water causes a hydration or gray mottling discoloration to develop. I do not believe there is any evidence, study, or scientific basis for that claim. Rain is far more aggressive than soft tap water that fills many pools and doesn't cause a supposed hydration problem for cement buildings, sidewalks, or driveways to turn a dark gray color.

On one hand, simply warming up a plaster surface to help the hydration and hardening process (while newly plastering) may be okay, but that practice will probably get out of hand and be easily overdone and damage the structural integrity of the plaster. But draining an existing plaster pool that is discolored (graying) and suggest that it is okay to torch the plaster and to make a gray and discolored surface turn "white" is okay is simply wrong. Once the plaster whitens means that the torching process probably went too far. Removing the water content within the plaster matrix is not a good thing to do, and it is likely that the torching heat was high enough to cause expansion and porosity and whiten in color. That simply ages a plaster surface that will degrade far quicker than usual.

The chemical reactions cited in that article are not accurate. Carbonation of the immediate plaster surface has already occurred due to being submerged in water. The extreme heating of calcium hydroxide (within the plaster matrix) is likely to drive off the water content and create calcium oxide, not calcium carbonate. Plaster can also re-absorb water again when submerged again.

That article does not mention that a main cause of gray mottling discoloration (incorrectly cited as a hydration problem) is caused by excessively late and hard troweling. And that can occur on both gray (concrete) and white cement applications. That provides cover for performing improper plastering practices. And let's remember that torching is cheaper than re-plastering, allows for the blaming of the problem on the water balance, and the pool will probably need re-plastering much sooner than normal due to the structural plaster matrix damage caused by over torching.
 
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bdavis466

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Aug 4, 2014
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San Clemente, CA
During my AquaBright era I became well acquainted with torching plaster – not so much for aesthetic reasons by to dry and prepare the surface to get recoated.

Several of the pools had the light grey discoloration being discussed here and it was often hard to tell if the surface was discolored or if it was still wet. I would apply heat with a weed burner torch and saw firsthand it often did correct the greyness but it also left the surface rougher than other areas. This is in pools with new plaster less 24 hours old.

The moisture in the plaster has to get heated to the point that it evaporates and turns into a gas. This gas must escape so it travels along the natural voids in the plaster until it surfaces. Since the surface is sealed by trowel, slight spalling occurs which removes the smooth outer surface and exposes the less dense inner section of the plaster.

I don’t see how anyone can say that torching newly applied plaster is harmless. Hydration is essential for curing the plaster and these same crews likely toss the hose in immediately after troweling to combat shrinkage cracks so torching an area is voluntarily doing the damage that they are trying to prevent in the first place.
 
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