Eroding Plaster


LifeTime Supporter
Feb 3, 2010
Hello All, So I've finally gotten the chemistry of my pool under control using BBB, thanks to you all. Now on to tackle a surface problem I'm having.

When I did a 75% drain on my pool to get rid of the calcium hardness and CYA, I also did some cleaning. I hit the block border with muriatic acid to take care of the calcium build up. And when the pool still had about 8 inches of water in the shallow end, I decided to take a scrub brush to an area that appeared to have some sort of stain. Well when I scrubbed it the surface gave way and turned into grit, revealing a dark material beneath it. Picture follows.
[attachment=1:213qxl00]IMG_4423 c.jpg[/attachment:213qxl00]
[attachment=0:213qxl00]IMG_4425 b.jpg[/attachment:213qxl00]
So two questions: What does my surface material look like (plaster, epoxy, etc.)? Second, what can I do about the erosion. Can it be patched? Can a matching patch be made or will I have to live with a noticeable blemish?

Facts: I've only owned the pool/home for 3 months. Don't have any history on it. Pool is about 5 years old.

There is also some staining that seems much more prominent when my FC gets low (outlined in the photo). Algae?

As always, thanks for the help. It feels so much better when you know what's going on instead of being at the mercy of whomever wants your money!




TFP Expert
May 20, 2007
South Central NJ
How strong was the acid solution you used? I hope you diluted it first.

The yellowing is likely to be calcium scale.

Post your pool chem numbers.



LifeTime Supporter
Feb 3, 2010
Hey Scott, No dilution! What's a little blistering and lung scarring amongst men??

Really though, I had gloves and a respirator (from work) and used a spray bottle. I used only about 1.5 pints for the whole border of block on my pool, and the border is only block at the top edge. When I refilled the pool the ph was only off by about .3 (really couldn't measure any closer).

But the spots in the picture were there since we moved in (~3 months). I'd used the pool brush on them before, but never a regular scrub brush until the big drain.

Numbers as of yesterday afternoon:
FC 5
CC 0
ph 7.4
CH 280
CYA 60

I use BBB and got off of pucks after the big drain.

Thanks for any help.



I can't tell from the pictures what your finish is (it looks a little bit like 3M or similar, but I'm not sure), but you do appear to have quite a bit of scale build up on the finish. When you scrubbed it, did it leave a depression in the finish, or did the surface material "crumble" and then this dark area appear (still on top of the finish)?

It looks to me like someone (not you, since you have not had the pool long enough) allowed the water to either get very hard or the pH to get very high and you are dealing with a lot of surface scaling. Some finishes are more durable than others and will take an acid wash, which will remove most of that. If you can find out what your finish is (maybe from the previous owners or if you know who built the pool), please post back (or PM me) and we can let you know how durable it is and what options you may have.


LifeTime Supporter
Feb 3, 2010
When I got the pool and you all got me spun up on chemistry, I tested the pool and CYA and CH were off the charts. That's why I did the dump and fill. But the spots that I have outlined in circles in the photo were there all along. Only when I scrubbed them vigorously during the dump, the surface "crumbled" exactly as you describe. Now there is a depression of about 1/16 of an inch and it's significantly darker.

I can't get any information about the pool. Previous owner won't contact me despite some very humble attempts (foreclosure).

Should I call a pro about evaluation and repair? Anyone have a reputable recommendation in the Tampa Bay area?

Thanks, Jim.


Can you check with your City and see if there is a permit on file for the pool build? That might get you some insight on who the builder was (if they pulled the permit).

Please get as much knowledge as you can. If I came out to look at your pool and it was/is just scale, I would tell you that. However, some others may just try to "scare" you in to doing a re-plaster to make a sale. If you can arm yourself with as much knowledge as possible, or find an honest estimator, then you will get an accurate assessment of what does or does not need to be done.

I'm on the "wrong" coast to get you a referral :oops: I do see an awful lot of pools a week though, and sometimes work is needed and other times it is not. I give an honest opinion of the pool if it makes me any money or not. Just a lot better way to do business, in my opinion. I see nothing from your photos that put you at "critical mass" to do work on an accelerated time frame. You have time to learn and make an educated decision here.
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