Gray spots on plaster in spa

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CFlaPool

CFlaPool

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Apr 21, 2021
166
Satellite Beach, Florida
Pool Size
21000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
These spots just starting showing up in the last month. Pool remodel was completed in Oct2020. They are gray, and do not seem to go away with a wire brush. They may get a bit lighter after wire brushing, but then come back. They are only on the horizontal surfaces of the spa. I. Had been running the pool in spillway for 40 minutes in morning and then in evening. I just added a midday 40 minute spillway to the schedule. It runs at 2400 rpm. Pool chemistry has been good, although I have not tested the spa water. I will do that. My signature describes the pool. You guys always seem to have the answers, so have it. Pictures below. I have not drained the spa, but that is easily done. I did just install a new filter so that is good. I have used no algacides.

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Copper staining can take on the color of a blackish grey. Although it doesn’t look like the copper staining I’ve seen. Without a stain I’d kit everything may be a guess. What’s the history on the heater, has it always been in your care? Do you have the ingredients or know of the brand of the sealant? Have you used vitamin c tablets to rule out iron?
 
I have used no algaecides so no copper. I saw copper on an old thread here. I think my next step is to test the spa water tomorrow, and drain it to get a better idea of the spots. I thought the wire brush had gotten rid of them, but they returned. We have not used the heater/spa in 4-6 weeks while these spots appeared. No spots have appeared in the pool, not on the steps nor the benches.

I have only used CYA and acid in the pool since the remodel (Oct 2020). Plus salt, of course.

Heater is from 2010, boards replaced in 2018. More details in signature.
 
Poolbreh said:
They look like calcium nodules to me, see if you can scrape a small amount off and carefully test in a vial with diluted MA and water for a reaction, or vinegar.
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The spa was brand new gunite and plaster, not a resurface like the pool was. I do see a few nodules (very white) on a couple areas of the pool walls, and researched those on this site.
 
ajw22 said:

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...
www.troublefreepool.com www.troublefreepool.com

Plaster Installation and Maintenance - Further Reading

www.troublefreepool.com www.troublefreepool.com
Click to expand...
Thanks. It was not until 3 years of age that these spots just appeared. So I am hoping that the use of CC 3% is not the problem. I did find this comment to that thread:

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...
www.troublefreepool.com www.troublefreepool.com
which may indicate scaling deposits. I have seen more deposits on the pool tile below the waterfall, so it could be scaling. I guess I'll find out more when I empty it today/tomrrow.
 
IMG_4974.jpegI just emptied the spa to below the benches. I am seeing white calcium nodules on the walls. The spots on the benches are deposits of some kind. I will follow-up with test results of the spa water. The spa was new gunite and plaster, so are those really nodules on the walls?IMG_4975.jpeg
 
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CFlaPool said:
View attachment 560231I just emptied the spa to below the benches. I am seeing white calcium nodules on the walls. The spots on the benches are deposits of some kind. I will follow-up with test results of the spa water. The spa was new gunite and plaster, so are those really nodules on the walls?View attachment 560233
Click to expand...
Spa water tests mirrored the pool water results above.
 
I do not have an answer for what has caused the smooth grey spots on the spa bench. Those spots are not caused by unbalanced water. Perhaps something fell into the spa and caused stains to develop.
The following post should explain the white calcium deposits on the walls.

Unusual Calcium Nodules

Calcium Nodules In 1998, the onBalance team published a paper in the Journal of the Swimming Pool and Spa Industry (JSPSI) on calcium nodule formation. The paper provided the science and mechanics for the cause of calcium carbonate nodules developing in pools. It explained that delaminated...
www.troublefreepool.com www.troublefreepool.com
 
onBalance said:
I do not have an answer for what has caused the smooth grey spots on the spa bench. Those spots are not caused by unbalanced water. Perhaps something fell into the spa and caused stains to develop.
The following post should explain the white calcium deposits on the walls.

Unusual Calcium Nodules

Calcium Nodules In 1998, the onBalance team published a paper in the Journal of the Swimming Pool and Spa Industry (JSPSI) on calcium nodule formation. The paper provided the science and mechanics for the cause of calcium carbonate nodules developing in pools. It explained that delaminated...
www.troublefreepool.com www.troublefreepool.com
Click to expand...
Thanks. After draining the spa below the benches, the gray spots are indeed deposits of some kind. They throw shadows. They seem the same in color/consistency as the deposits on the tile below the spillway. The pavers were re-sanded and re-sealed in October using a water based two-part sealer. Maybe some of it got into the spa and has finally congealed? There was plenty of stray sand in the pool that took some frequent vacuuming and filter-cleaning to get rid of. I replaced the pool filter after getting it cleaned out.

If this is scaling, like on the wall tile, what is best to use to remove it? If MA, what dlution?

The calcium nodules on the wall (which scrape off quite easily) perplexed me because the spa was new construction, replacing an acrylic shell spa. Your link above could explain them, although I would have to look more closely to see any cracks, which were not immdediately visible. I had read the other threads on nodules from delamination, but had not seen the one you linked to.
 
onBalance said:
This plaster nodule problem should not be controversial. Those who maintain the pool water chemistry should not be blamed for causing this plaster problem. And unfortunately, there are other plaster defects that are being (incorrectly) blamed on aggressive water chemistry also. This nonsense needs to end.
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From onBalance article. You can gently use 60 grit sand paper. Or a diamond sanding hand pad.
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I would not use MA on the plaster. Unfortunately they will continue to come back.
 
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Poolbreh said:
From onBalance article. You can gently use 60 grit sand paper. Or a diamond sanding hand pad.
View attachment 560271
I would not use MA on the plaster. Unfortunately they will continue to come back.
Click to expand...
Update: The gray spots looked to be from the paver sealant. That is my best guess. Next time it gets sealed, I'll get a cover and protect the water. The sealant could have run down the coping stone and eventually made it into the water. I guess it took 5-6 months for the sealant to coagulate, harden and turn gray. I broken the outer shell of the deposits with the aluminum handle on brush lightly, and then was able to lightly steel-brush the deposits off.

The nodules on the walls scraped off quite easily, lightly with the brush handle and then very lightly with the steel brush.

After a fresh fill, the spa looks great. Thanks for all the help! Now I have to get the new temp sensor installed, but that's another thread I have here.

Thanks again!
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IMG_4980.jpeg
 
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