Trying to understand blotchy plaster finish.

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T

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In The Industry
Jul 2, 2012
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Saugerties, NY
I've worked with vinyl liner pools for a long time, only dealing with concrete/plaster pools in a limited capacity. Recently, I've been finding myself a bit more involved with new concrete/plaster pools, and I'm trying to learn what I can to make sure these pools are being treated right. In the past two seasons, I've picked up three new plaster finished pools. The finish varies between the three in terms of uniformity. So I'm wondering why. What causes the blotchy appearance on a plaster pool? Is it just the nature of a plaster pool? I've talked to some other pool pros that deal with plaster pools, and they have said that if the pool wasn't brushed well during the first few weeks, there will be calcium build up. Of the three pools I deal with, one was brushed by a caretaker, another by the customer, and another by pool guys. None of them have an even uniform color.

I was just hired to brush down a pool that was refinished, and I want to make sure that I am doing whatever I can to make the finish look right. My plan is to brush daily for the first week, then 3 times a week for the next three.

I did the first brush down today, and I didn't see any difference in the appearance after brushing an area. I didn't see any cloudiness coming off the bottom as the brush passed over it. I was kind of expecting to see something. I'm already seeing some blotches in this pool, and it was only filled yesterday. The chemistry was pretty good. TA was a little bit high, otherwise it looked good.

I'd appreciate any guidance you guys can offer.
 
Try a search for the posts by OnBalance. He makes a lot of great posts discussing plaster and how application can causes issues down the road.

This will get you started: http://www.troublefreepool.com/search.php?searchid=318854

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After my pool was done (Pebblesheen Blue Granite), one of the techs remarked that it was one of the most even applications he had seen. It does seem like having mottling is very come and worse the darker the finish.
 
Sometimes plasterers add calcium chloride to dark color pigmented plaster. That is not recommended. And adding water while troweling is also the wrong program. Combined, that will cause light or white blotchiness or streaks. Both issues create increased porosity in time, and it can take a few weeks to begin showing up. High porosity shows up as very light in color in contrast to the dense surrounding surface.

Organic pigments are also very problematic. Chlorine can bleach those type of color pigments (or dyes).
 
This is slightly off topic of your original question but since you're taking care of other folks colored plaster pools you should know that colored plaster is much more sensitive to chemical additions and you can easily induce off-colored spots and marks by allowing dry chemicals to sit on the plaster surface. That's especially likely as winter approaches and water temperatures get lower and it takes much longer for chemicals to dissolve. Undissolved powdered chlorine, dry acid, stabilizer and even calcium chloride will permanently discolor colored plaster even when in contact for very short periods of time. Don't let any chemical sit on the bottom of a colored plaster pool for more than a few seconds without brushing it until it's completely dissolved. Best to pre-dissolve all chemicals, even if the container instructions say not to do that (i.e. calcium chloride). Accidentally damaging the color of a client's plaster would not be a comfortable situation.
 
It is true that pool chemicals can cause certain types of staining if left un-dissolved on the plaster surface. Also, chemical stains would generally be easy to determine due to the pattern and location of the stains.

Acidic chlorine sanitizers and dry acid would not normally cause immediate white blotchiness of dark color plaster. Calcium chloride might, but could be removed. Light color or white blotchiness that slowly appears over time is generally caused by what I wrote above, especially if it occurs on the walls of the pool. These types of issues and problems are often over-looked.
 
I certainly don't make a habit of letting chemicals sit on the bottom of pools. I have learned in the past few days that there is a difference between brushing a pool, and really brushing a pool. The blotchiness I saw was calcium. After some really intensive scrubbing with a wire brush, the white patches have gone away.

I certainly wasn't expecting this to be as difficult as it is. I spent 2 1/2 hours last night scrubbing down this pool, and I spent another 1 1/2 hours again today. My arms and shoulders are killing me. I'll be back at it again tomorrow as well. The pool still isn't quite as uniform in color as I'd like to see, but it is much better.
 

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