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Thread: Plaster staining

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    EvilTwin's Avatar
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    Plaster staining

    I am hoping this is the right place to post this. Please move if appropriate.

    So since I now have my basic day-to-day maintenance covered and the pool seems to be remaining rather sparkly, I want to start tackling some of the other issues. One of the things about having such clear water is that it makes it easy to see stains. It would seem that the entire surface of the pool is covered in what appear to be these irregularly shaped stains. They tend to be bluer lines, with browner lines outside them. They aren't 'in your face' kind of stains (though I do have a few of those which I suspect are rust spots) but they seem to make the pool appear more dingy. Pictures attached are taken of what was on the steps. I am looking for some thoughts on what they might be and how to address them. The pool is plaster, approx 20 years old. Previous owner seemed to be using pucks. PH and CYA were very high when we opened the pool in May.

    I have tried brushing the stains but it doesn't help. Speaking of brushing, when I do brush (using a stainless bristle brush) I get a fair amount of substance off of the pool surface that cluods the water for a bit and disappears. is that normal? How often should I be brushing the pool walls and bottom?





    Also, disregard the stain marks in the upper left of the second photo. They came from a pump I set there when pumping the pool out. I am interested in the general staining that is seen over all of the plaster.
    ----------------------------------------------------
    25000 (?) gallon Plaster IG roman-end pool (18x36, give or take, 8 ft deep end), 7 ft round spa-spillover to pool
    Nautilis FNS-48 DE Filter, disconnected separation tank
    1.5HP single speed main pump. 3/4 HP pressure-side cleaner pump.

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    mrcarcrazy's Avatar
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    Re: Plaster staining

    I don't know about the discoloration, but the white dust sounds a lot like plaster dust on a new pool....what's your pH?

    I also don't know about using a metal brush regularly. I'd opt for a less aggressive brush.
    IG gunite/plaster pool/spa Started 1/17/14, Plastered 5/16/14
    Size: 12'-21'x39' free form, depth ranging from 4' to 7, attached 6 person spa with spillover.
    Equipment: Whisperflo 2hp pump, Pentair 30" sand filter, Pentair Mastertemp 400k BTU heater, 1hp Whisperflo for waterfalls, and a blower for spa floor

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    EvilTwin's Avatar
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    Re: Plaster staining

    Quote Originally Posted by mrcarcrazy View Post
    I don't know about the discoloration, but the white dust sounds a lot like plaster dust on a new pool....what's your pH?
    The pool is 20 years old, so if it is plaster dust I think I'd be worried it was coming off so easy. PH is around 7.5 now

    I have a nylon brush too. I was just under the impression that nylon=liner, SS=plaster/concrete. I'll try the nylon.
    ----------------------------------------------------
    25000 (?) gallon Plaster IG roman-end pool (18x36, give or take, 8 ft deep end), 7 ft round spa-spillover to pool
    Nautilis FNS-48 DE Filter, disconnected separation tank
    1.5HP single speed main pump. 3/4 HP pressure-side cleaner pump.

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    EvilTwin's Avatar
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    Re: Plaster staining

    So I came home today and since I have a day or two where the pool isn't getting used, I did another large water drain/refill to lower the CYA level. Took more pics of the plaster with the water down. The darker areas appear and feel smoother than the lighter ones. The lighter areas are what appear blue/brown when under water.



    Also have this staining problem under the shallow end rope tie

    ----------------------------------------------------
    25000 (?) gallon Plaster IG roman-end pool (18x36, give or take, 8 ft deep end), 7 ft round spa-spillover to pool
    Nautilis FNS-48 DE Filter, disconnected separation tank
    1.5HP single speed main pump. 3/4 HP pressure-side cleaner pump.

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    EvilTwin's Avatar
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    Re: Plaster staining

    After refilling the pool with the 18 inches of water I drained and retesting, my CH dropped to 180. Given this statement from pool school:

    If there is too little calcium in the water, and you have a surface containing calcium (plaster / marcite / pebble / grout), calcium from the pool surface can dissolve into the water, causing pitting and deterioration thereby shortening the life of your finish.
    I am wondering if the CH has been low over the years due to well/refill water and poor maintenance of the water chemistry in this regard.
    ----------------------------------------------------
    25000 (?) gallon Plaster IG roman-end pool (18x36, give or take, 8 ft deep end), 7 ft round spa-spillover to pool
    Nautilis FNS-48 DE Filter, disconnected separation tank
    1.5HP single speed main pump. 3/4 HP pressure-side cleaner pump.

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    Re: Plaster staining

    As you stated, the plaster is 20 years old, and wearing out. There is no simple way to make the plaster uniform in color again.

    The whiter areas are due to the fact that those areas are very porous now (probably from wet troweling during construction) and have turned blue or brown from copper and iron adhering to those porous areas. Because of the porosity, plaster material (calcium hydroxide) is probably being dissolved and mixing into the pool water. But you have never stated what your TA and CH to determine whether the water is aggressive or scale forming. That might be helpful to know.

    The smooth and darker gray areas was probably more effectively hard troweled and has remained intact and dense throughout the 20 years.

    The black stains next to the rope ties is from iron metal (likely rebar) underneath and rusting through to the plaster surface. That can be fixed by chiseling out the plaster and down to the rebar and cut out, sealed, and re-patched.

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    EvilTwin's Avatar
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    Re: Plaster staining

    Quote Originally Posted by onBalance View Post
    But you have never stated what your TA and CH to determine whether the water is aggressive or scale forming. That might be helpful to know.
    Thanks for replying. As of today CH is 180 (down from 210, just did a partial drain and refill). TA is 120.
    ----------------------------------------------------
    25000 (?) gallon Plaster IG roman-end pool (18x36, give or take, 8 ft deep end), 7 ft round spa-spillover to pool
    Nautilis FNS-48 DE Filter, disconnected separation tank
    1.5HP single speed main pump. 3/4 HP pressure-side cleaner pump.

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    Re: Plaster staining

    Your pool water balance appears to be within the proper range, as long as your CYA isn't too high.
    So no concerns there. Just keep doing what you are doing.

    Your plaster is what it is. At some point, you can have it re-plastered, for a brand new look!

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