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Thread: Plaster stains appearing in new plaster

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    Join Date
    May 2012
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    Philadelphia, PA
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    Plaster stains appearing in new plaster

    Hello Everyone!

    I had my pool replastered (white) last August (10 months ago). Since opening the pool this spring, there are many areas of grey stains appearing on the floor. Some of the stains actually look like dirt resting on the floor, shaped in a swirl moving towards the main drain. Nothing at all on the walls. Brushing the pool with nylon brush certainly does not have any impact on the stains. If I feel the surface where the stains are, it feels rough on the surface, similar to sandpaper. Is this a sign of calcium scaling? Is this something that could have been caused by improper workmanship during the plastering?

    If there is a way to remove the stains without draining the pool and doing an acid wash, that would certainly be my preference. I am about to try using direct application of muriatic acid to a couple of spots combined with elbow grease and a stiff wire brush, to see if this has any impact on the stains. However, I wanted to do my homework first to make sure I am taking the best approach.

    Here are my recent water test results:
    FC: 4
    pH: 7.8
    TA: 90
    CYA: 35
    CH: 200
    TDS: 450

    I will post some pictures shortly.

    I would appreciate your feedback and suggestions on how to move forward.

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    duraleigh's Avatar
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    Re: Plaster stains appearing in new plaster

    Welcome to the forum. It sounds like calcium scale. Your current numbers would not indicate a scaling condition but, if they are pool store numbers, I have no faith in them.

    The pic would [probably help.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Plaster stains appearing in new plaster

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    Re: Plaster stains appearing in new plaster

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    Re: Plaster stains appearing in new plaster

    To me, the discoloration doesn't look like calcium scaling, but rather severe gray mottling caused by improper troweling. Interestingly, it usually takes a few months show up, so don't let that fool you.
    It also may be both gray mottling initially and calcium scale (roughtness) over the top of it. However, if you were to put acid into a squeeze bottle and apply directly to the dark stain and it removes the discoloration quickly, then it is calcium scale that has dirt and minerals combined to create the darker color. You could also try some 100 grit sandpapaer and see if that removes the dark discoloration. If the roughness is removed, but not the discoloration, then it is gray mottling. If either method removes the discoloration and the plaster becomes white again, then it is a calcium scale precipitation problem and a water chemistry (high pH) issue during the winter time.

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