wondering about a no drain acid wash

[rhythm]

Hello all, I'm wondering about doing a no drain acid wash due to the recent appearance of my plaster. The plaster is about 10 years old now, and a few months ago it started looking 'dirty' on the bottom. I'm not sure if it's some kind of staining, or something precipitated onto the plaster surface, or ?? I've attached some pictures, and here are some additional observations:

At the darker areas, the plaster is not as smooth as it normally was. The areas that still look white are still as smooth as ever.

The 'patterns' you see have been there since the first year we had the pool, but were always very smooth and were a very light gray-bluish pleasant looking color (not dark or brown-ish like now). I think it may have been due to something with the way the pool was originally plastered, but it was never unpleasant to look at until now.

If I lightly sand a spot, it does get a bit smoother, but the color does not go away. I have not tried sanding very aggressively yet in any spot, though, to see what will happen.

There have been plenty of times over the 10 year period that I've let the pH get to around 8.0, but it was always very temporary. Our fill water is quite hard, so we've always had a pretty high hardness reading for our pool water. TA has normally been between 80-100, pH normally around 7.6.

Rubbing a spot with vitamin C didn't do anything for a stained area.

In bright sunlight it's not too noticeable, but in shade...different story.

There are a couple of spots in the pool where the bottom has a regular flow of water over it (a low return in the deep end, and below the spillover spa in the shallow end), and both of these areas still look unaffected (white and smooth).


So, as I mentioned I'm thinking about trying the no drain acid wash and seeing if it will help. But first I would like to try and find out what this is before taking action. Thoughts? Or questions for me?


Thank you,
Greg

 

[mas985]

Before trying an acid treatment, we should figure out what that is.

You tried Vitamin C but did you try chlorine (tab)? If organic, they should lift.

If chlorine does not lift the stain, try a small bag of dry acid on a spot and see if that lifts the stain. If so, it might be scale.

 

[gwegan]

+1 to what Mark said.

 

[rhythm]

Thanks for the replies. I tried a chlorine tablet today and no luck. I rubbed it pretty good on a few spots. Should I leave the tablet sitting on a spot for a while, or should 10-20 seconds of rubbing it on a spot be enough to see some result?

I still need to get some dry acid. What I may try tomorrow is draining my spa a few inches so the top step is flush with the water line, and take a rag with some muriatic acid and try it on a couple of spots.


-Greg

 

[rhythm]

OK, I finally got around to trying some acid, and it definitely had an effect. I drained my spa a bit so that the water was right about the same level as the top step. In a bucket I added some muriatic acid to some pool water. With gloves on (of course) I dipped an old hand towel into the diluted acid and began applying/rubbing it on the top step, and after a few applications/rinses the top step is much whiter again. When I began doing this, there was a very slight 'hiss' and a little bit of visible "off-gassing" (almost looks like white smoke), just like when I use muriatic acid to get rid of the scale/efflorescence that builds up on the tile underneath our water features and natural stone.

The slight roughness of the dark colored areas was gone, but the resulting whiter plaster didn't seem quite as smooth as unaffected spots in the pool. I don't know if more acid application would smooth it out or make it worse, but I didn't want to keep going. The plaster is about 10 years old. There are some spots here and there that are worse than most areas, where it almost seems like sand grains. There were a couple on the top step, and they went away after a few acid rubbings.

As I mentioned, the result on the top step is that the plaster is whiter and a bit smoother than the brown areas, but not as smooth as the white areas in the pool that are not yet affected. So I'm not sure what to do. If a no-drain acid wash is performed, the pool may look a lot better, but am I running the risk of it being a bit rough when I'm done? What do you think?


Thanks,
Greg

 

[mikemass]

The the acid solution fizz up and turn yellow when you did this:

I dipped an old hand towel into the diluted acid and began applying/rubbing it on the top step

 

[rhythm]

I heard some fizzing, but didn't really notice a yellow color. There could have been a little perhaps, but not to the point where I remember it being that color. The darker areas on the top spa step were not as pronounced as much of the rest of the pool, so perhaps I wasn't taking off too much scale in the area that I worked. (If in fact it is scale).

 

[mikemass]

Fizzing good. Means it's attacking scale. But it will etch the plaster too.

Acid washing is a slippery subject. Sometimes it's a necessary evil. But if your expectations are to get your plaster feeling like the day it was applied, you won't be happy. Looks? Yes! (nice and white now right?) Smooth feel? Not so much. Sorry to be the bearer of bad news but plaster pools do not have an unlimited life expectancy.

 

[rhythm]

I hear what you're saying. Even without doing anything with acid I know my plaster is no longer as smooth as it was a long time ago, so I wasn't expecting any miracles in that area. I'm pretty sure, though, that the area I treated today is a bit smoother than the areas with the scale, so this still may be an improvement overall in the smoothness department as well as the look. If the scale was only in a few small areas I wouldn't bother, but it's most of the pool now. This weekend when I'm in the pool I'll let my feet determine what I think about the step I just treated vs. the rest of the pool. If I decide to try the no-drain acid wash, I may just try the spa first and see if I like the results enough to do the pool afterward.

 

[mas985]

If it is scale, you can try this method to see if it helps:

The Zero Alkalinity Acid Treatment

 

[rhythm]

If it is scale, you can try this method to see if it helps:

The Zero Alkalinity Acid Treatment

Yes, this is exactly what I was wondering about doing. I'll probably try it in just the spa portion first to see how it goes before trying it on the entire pool.


-Greg

 

[friguy3]

Have this issue too. New house with 8 yr old pool. Opened it and the pH was >>8. The walls and floor are super rough just like sandpaper and there is exactly that dark look to the floors. I took and putty knife and sandpaper to it. It helps the roughness, somewhat. Color, Nada. Think it comes back? Was going the acid wash route and now thinking...will replaster with pebblesheen or something like it. ?

Sent from my SM-N920V using Tapatalk

 

[rhythm]

By the way, when I do the no drain acid wash, will the 'released' calcium in the water be filtered out (so I can do backwashes and get rid of it)? Or would I need to do a partial drain and refill to take care of the resulting rise in calcium hardness (which would be very undesirable right now in Southern California)?

Thanks,
Greg

 

[mas985]

The calcium carbonate will be dissolved in the water and cannot be filtered out.

However, there is a method floating around somewhere, where if you raise the PH quick enough and the CSI high enough the calcium carbonate will fall out of solution and can be vacuumed to waste but I have no idea if this would work or not.

You might PM OnBalance and see if he has any suggestions.

 

[rhythm]

Thought I'd post an update. I started the no-drain acid wash process in the spillover spa only, to see what kind of result I get before moving on to the pool. I put the acid in the spa about noon on Saturday, so we're approaching 3 full days. Overall, it appears to be working. The brown scale areas have greatly faded everywhere, and in many spots it seems to be completely gone. Overall it's not quite as fully 'clean' as the top step in the spa where I used a rag with an acid/water mix directly on it for a little while, but it's getting closer. I've been brushing every several hours with a small stainless steel brush (more frequently the first 24 hours). When I brush, the water definitely gets cloudy. I'm thinking I'll bring the TA back up tomorrow after I get home from work, which will be a total of 4 days plus 5-6 hours. If you're wondering, I used about 3/4 of a pint of 31.45% strength MA. The spa is around 700 gallons and my TA was at 60 before I added the acid.

-Greg