Need help with plaster spotting or etching

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C

C0d3Sp4c3

Well-known member
Dec 10, 2018
258
Inland Empire, CA
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
Last year, our pool with raised spa received a new plaster and the water chemistry stays in check using the tfp method, since. About 3 months ago, the spa developed some unsightly brown spots at the bottom and the surface became rough like sandpaper. There is no noticeable plaster discoloration on the wall except for some rough streaks that can be easily smoothened using pumice or sharpening stone only to re-occur days later. Brushing, chlorine tablet and vitamin C has no effect on the brown spots that are multiplying at a fast rate.
We heat the spa on occasion and wife suspected the heater elements being too old. I would like to agree but the spa spillover to the pool when not in use. Yet, there is no sign of brown spotting in the pool. Again, improper water chemistry is out of the question. Is there anything I should do to stop the spotting or etching? My apology for lack of better terms but I'm all ears.Spa_brown_staining.jpg
 
Please post your test results:

FC
CC
pH
TA
CH
CYA
Salt
Borates
CSI
Water temp

Do you use PoolMath to log your tests and chemical additions?

What heater do you have? There is no heater listed in your signature.

Have you had your water tested for metals? Especially copper?
 
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Hi Allen, thank you for the response.
I have been regularly lurking this forum ever since I inherited an old pool 4 years ago and I knew this is coming.
Today's K-2006 test results:
FC = 6
CC = 0
pH = 7.6
TA = 80
CH =450
CYA =60
Salt =3200
Borates = 0 (never use)
CSI = -0.07
Water temp = 80°F
Yes, I used PoolMath many times in the past. I don't keep log nor record the results but I still test the water once a week and perform a full test once a month. As a retiree, I start my day by inspecting the pool and equipment making sure everything checks out. Sorry, the label on our dinosaur heater is unreadable but my past searches suggested it is a Hayward H-series Millivolt ED1 type. Still working good though.

Although pool store testing is frown upon here, I always bring samples to Leslies to avail of the $5 discount whenever I'm low on MA.
Iron = 0.0
Copper = 0.0
Phosphate = >500 ppb
At this time of the year, it is expected for my ph to creeps up faster and I am running low on MA. I will bring a sample to Leslies anytime soon and will update.

Anyway, can I assume that this is the condition that Onbalance has written about and would there be any fix other than "live with it"? Thank you
White Spotting of New Plaster Pools
 
If you are speaking of the very dark, small, and pronounced brown stains on the bottom, then that appears to be caused by a few pieces of small iron fragments that is rusting and leaving a stain somewhere different every day. I suggest you try to find the few metal pieces and remove them. Next, get some 100 grit wet & dry sandpaper to sand off those brown spots. That will work better than vitamin C. That will also make the plaster surface very smooth after sanding.

If I am correct about this, then obviously this would have nothing to do with poor plastering or unbalanced water.
 
Thank you onBalance for chiming in, much appreciated.

Indeed, first I thought it was some kind of metal shavings but a speaker magnet did not pick any microscopic particles. From what I observed, the scattered brown spots are raised and scrubbing them with a sharpening stone makes them level to the surrounding plaster but remains brown. At one point, I emptied the spa in an attempt to investigate deeper. Equipped with a small screwdriver, I tried to pry one of the spots on the bench. Well, it did not turn out good and I just made a tiny brownish hole in the plaster. I must say the brown spots are buried deep in the plaster and growing like pimples. Also, I must add there are no brown spots on the wall but streaks, like termite trails (for lack of better words) rough enough to scratched bathers. I can sand them off easily with a sharpening stone, only to re-appear days later.

Just hard to imagine that the once very smooth surface turned into sandpaper in a very short period of time and I am out of ideas.
 
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Very strange, and I am at a loss to understand what has happened. I wonder if there is rust coming up from the steel rebar beneath the plaster?

As for the rough streaks on the spa walls, check this post out for a possibility of that problem.

Calcium Nodules in pools

What are calcium nodules? In swimming pools and spas, they are small mounds, bumps, deposits, or “slag” piles of calcium carbonate which are formed from material that has been released from the plaster. The small calcium nodules are rough to the touch, hard, and generally gritty. Nodules may...
www.troublefreepool.com www.troublefreepool.com
 
I wasn't sure about the nodules but thank you for the link.
I trust my own testing but Leslies is my preferred source for MA @31.45%. Today I brought samples and posted the results below vs taylor test in post# 3.

I mentioned about the scattered brown spots and without hesitation, she said it is black algae. She added that black algae can sometimes brown in color. She also told me what color to expect from different sources of contaminants and blah, blah, blah. Well, I found myself walking out of the store fully educated :geek:

Black algae, hmmm! I recall last March a couple from MN visited us and we allowed them to drink in the spa. Not sure if they somehow spilled beer in the water or maybe, just maybe their swimwears are contaminated. Well, my search for black algae has no resemblance to the issue I am having with. Then weeks after that, I witnessed a kid accidentally tipped over a 19 oz tumbler filled with mango juice and everything went in the spa. :oops:

Anyway, I think I can learn to live with it as long as the brown spots will not spread into the pool. What happens in the spa stays in the spa o_O Thank you

Leslies water test.jpg
 
1) when you had the spa re-plastered, did you have any repairs or rust spots repaired? Do you recall them cutting any rebar or other metal? Fine splinters (what you see as sparks) can leave fine spots like what you are seeing.
2) fine iron (pebbles for a lack of better word) or even busted up ball bearings have found themselves into bags of pebble, however your finish appears to be white plaster.
3) any fertilizer put down recently?
4) I have seen calcium deposits break free out of old heat exchangers and sometimes they are dark with other minerals but almost always are removable without any lasting stains.

Black algae unlikely
Hope this helps
Cd
 
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When they did the replaster, did they chip out the old plaster?

It might be from wire ties that join rebar together.

Try a strong magnet directly on the spot to see if there's any attraction.
 

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Hi Cd.
Yes and no. I wish this is a case of rusty metal fragments bleeding out. As observed, it looks like the brown spots are embedded in the plaster.

1. There are a couple of areas on the bottom of the pool in the shallow end where exposed rebars were cut and patched. And another one on the wall by the sun shelf. I took pictures of that if in case rusting occurs in those areas. However, no rebar cutting/grinding took place in the spa or the adjacent area.
2. I agree. Yes, it is a standard white plaster.
On the day of plastering, the crew conducted acid wash to the gunite, rinse and drain with a sump pump. Then suck out debris using an industrial vacuum cleaner.
The spa received the first batch of plaster. Who knows, there might be some metal fragments trapped in the mixer from the previous job.
3. No, we don't use fertilizer and never will.
4. I wasn't sure about the calcium deposits but it's so true and I am not disagreeing with you.
The pool was re-plastered in January last year and so far, no visible signs of calcium deposits. I first started to notice a couple of brown spots in the spa (bench in particular) in May of this year and it quickly multiplies on the bottom as days go by. Otoh, the pool is spotless.
 
JamesW said:
When they did the replaster, did they chip out the old plaster?

It might be from wire ties that join rebar together.

Try a strong magnet directly on the spot to see if there's any attraction.
Click to expand...
Yes Sir, old plaster was chip out completely.

I have a 1" magnet pulled from a busted speaker but it didn't pick anything.

I am at a loss but indeed, I thank you all for your responses
 
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Last time I gently slide the magnet along the bench which is within arms reach. Next, I tied the magnet on a string, dropped it on the bottom and gently pull the string. To my disappointment, the results are inconclusive. The spots are no more than 1/4" and some are sitting close to each other. I can probably obtain better results if I have access to a handheld digital force gauge.

But let's say the problem is caused by metal staining, is there anything I should do or could have done to get rid of the stains other than new plaster? Just curious... and folks, I grew up in central europe. Please excuse my English and grammar if I may sound offensive. Thank you

Here's how it looks like today on a cloudy morning. The spots are more pronounced on a sunny day
 

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