Acid wash question

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J

jayatpitt

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May 6, 2013
43
I have a 30,000 gal pool with 800 gal attached spa. Have had scaling on the spa for years and I'm ready to take care of it. Was going to try an acid was first. What concentration muriatic acid should I have? I have the 31% stuff - how much would you recommend diluting it?

Scaling is only in the spa - pool is generally fine.
 
Acid wash is the most aggressive option and will remove plaster, damage the plaster and shorten the life of your plaster. Acid wash uses 31.45% MA, which is the strongest percentage, straight acid, no dilution start with 50/50 acid to water and go stronger if needed.

There are a few options from least to most aggressive
Sand the scale with @100 grit wet/dry sandpaper
Lower your pH to lower your CSI to -0.8 to -0.9 and brush frequently with a stainless steel brush
Do a no drain acid bath, The Zero Alkalinity Acid Treatment
Drain and acid wash the plaster

More about scale here, Pool School - Calcium Scaling
 
Richard320 said:
I find sheetrock sanding screens work the best, but they still disintegrate and leave a pile of dust to vacuum.
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Got it. I have a handy attachment for those that connect right to a shop vac - I'll start with that.

I'll post a pic of the issue just to be sure - I looked at it again this morning and thought to myself it looked really bad. When I opened the pool ph was really high - not sure how high cause it was off the charts. The spa is usually empty, but somehow filled up with water over the winter. I assume it was just sitting in the super high PH water for months.
 
skimmerswimmer said:
An acid wash is usually 3 or 4 parts water to one part acid. Better to start with a weaker solution and adjust or re-apply as needed.
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Ok, you made me go look it up. Acid wash is typically done with 50/50 to 75/25 acid to water and up to 100% if more strength is needed. I do agree starting weaker and going stronger if needed is best.
 
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That's the seat area of the spa - pretty bad.
 

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That's either Calcium scale or severely etched plaster. I can't tell if one part is raised or the other part is lowered.

It doesn't have to be supersmooth. I have a little bit of grittiness here and there -- not enough to cause road rash -- and it does give good traction.
 
Got it. Since I'm not sure if I'm dealing with calcium scale or severely etched plaster, I guess it's best to go with the sandpaper? I suppose I can test with some acid and see if I get the fizz....
 
Gave this a shot. Acid turns yellow and fizzs like crazy. I tried it in a few areas and it doesn't seem to take off enough to make any difference. Sandpaper works, but it's gonna be a chore. Started with the drywall screens, but they just get ripped up by the rough surface. Random orbit sander with 60 grit seems to work better. I'm just buying time at this point till i replaster - it's about 20 years old and has never need done. There are a couple areas (one small one really - size of a quarter) where it's so thin I think I can see the actual concrete (or whatever it is) below.
 
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