Stains and Mottling On Plaster - Remove and Prevent


Well-known member
Aug 20, 2017
Southeast PA
Hello all,

We're getting quotes for tile/coping work to fix some issues on an older (late 80's maybe) Anthony and Sylvan plaster pool. While doing that, we're trying to make the rest of it as perfect as possible.

We have some staining and then some off-color mottling all over. Three questions if you please:

1. The staining I'm pretty sure is organic but I don't have any tri-chlor pucks (why would I???? lol) to test with. Is there another way to test?

2. Is the mottling normal, anything that can be done? I read the deep end mottling thread (Gray Mottling Plaster Discoloration) but I think I have the type that they're saying is the light variations that are normal?

3. How do I prevent the staining? It mostly happens in the winter when it's closed, worms and debris get under the cover and sit until spring. I try to run the robot until the pool really freezes over, but this year it never really hard froze but was cold enough I had to take the robot out and put it inside eventually. I clean it in the spring when I open, but the stains will lighten but not go away completely. Should I leave the chlorine at shock value for a week or so and brush a bunch and run the robot and really try to get it taken care of in the spring? I'm at SLAM levels anyway for a day or two every spring, but usually it passes after the second night so I let it drift down.

Edit: Forgot to mention, even though the pool will be drained for the tile/coping work, the one guy I asked who was giving us a quote, said he wouldn't recommend an acid wash due to the age of the pool, it might be too thin already for that.


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