How White Pool Plaster Turns Blotchy

onBalance

TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
1,218
Utah
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.

CouponCCstudy3.jpg

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.
 
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Patrick_B

TFP Expert
LifeTime Supporter
Jun 7, 2011
15,006
Midland TX
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.
 

Gingermom

Member
Sep 16, 2017
15
Houston, TX
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.

View attachment 31086

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.
So this means my pool contractors comment that pools just do that over time, I should have done a different finish is really - no they did a bad job of finishing the plaster. Does it just get worse over time?
 

onBalance

TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
1,218
Utah
Not seeing any photos of your pool and knowing the age, I am unable to answer your question. The graying problem (of white plaster) that is discussed above occurs within the first year. If graying occurs after a year passes, then it is probably scale that has turned gray. Fortunately scale can be somewhat easy to removed.
Here are two other posts that you might find helpful. Or is your plaster a color other than white?

 
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