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Thread: How White Pool Plaster Turns Blotchy

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    Join Date
    Jul 2011
    Arizona & California

    How White Pool Plaster Turns Blotchy

    This experiment below explains how white pool plaster can become blotchy gray, and also have white areas mixed into the gray areas.

    Both white pool plaster coupons below have been in water for one year. Sometimes the water was slightly aggressive (negative CSI), and sometimes the water was slightly scale forming (positive CSI), but always within a good and proper range of -0.5 to +0.5 CSI. In other words, it follows a typical water chemistry balancing maintenance program of most residential pools for a one year period of time.

    The top coupon was formed with only one percent calcium chloride (CC) added to the mix, and was properly troweled. It remained a “uniform white” the entire time.
    The bottom coupon had 3% calcium chloride (CC) added, was late hard troweled, and also received some wet (water) troweling late in the process.


    Note the light and darker color contrast of the bottom coupon creating a “blotchy” appearance. The darker areas are very dense due to the hard troweling. The lighter (white) areas and spots are due to higher water-to-cement ratio and porosity from wet troweling. Had that coupon not been troweled with water, it probably would have been more overall gray due to the high CC and late hard troweling only.

    Sometimes, plasterers add 3% CC to a plaster mix to hurry up the hardening process and finish the pool faster. The plaster mix may harden so fast that the finishers can’t keep up. If the plaster is not smooth enough when the plaster becomes hard, the finishers may then splash water onto the surface to rework and soften up the plaster again in order to get it smooth.

    This experiment by onBalance demonstrates that improper troweling and workmanship can create non-uniform discolorations of pool plaster, and the mechanics of discoloration and blotchiness can be the same with dark colored plaster.
    Last edited by onBalance; 06-25-2014 at 03:36 PM. Reason: Changed picture

  2. Back To Top    #2
    Patrick_B's Avatar
    Join Date
    Jun 2011
    Midland TX

    Re: How White Pool Plaster Turns Blotchy

    Excellent post with great information as always!

    Thanks for sharing this with the forum. I often refer folks to your site for this sort of information. Always interesting.
    TFP Moderator
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    ABC's Of Pool Chemistry, Test Kits, SLAM Your Pool
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  3. Back To Top    #3
    Divin Dave's Avatar
    Join Date
    Oct 2013
    Longview, Texas

    Re: How White Pool Plaster Turns Blotchy

    I agree with Brushpup! Excellent on any level!
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge. Experience- it's what's learned just after you needed it most !!

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