Blotchy Plaster surface - anything to do?

[BenB]

Hi folks.

I'm mid drain and refill (76%) to reduce my very high calcium levels (1000). I know we generally advise against any kind of acid treatment but it's soooo tempting when looking at this...

Any thoughts? It's smooth all over but does fizz when I splashed some 1:5 MA onto a flat test area.

I have some raised hard nodules that I will be treating locally.

 

[mknauss]

Acid wash is your choice. It will remove some surface scale. It WILL remove some plaster. It will shorten the life of your plaster.

Another method is to run a very low (-0.6) CSI and brush alot. With high CH fill water, you would be best to use softened water for make up water after the initial fill.

 

[JoyfulNoise]

There will always be fizzing when you apply muriatic acid to plaster, that doesn’t really tell you much. An acid wash is not easy to do if you don’t have the right tools, chemicals, and a couple of people helping you. You can easily go from removing scale to damaging the plaster in a split second. It’s not something for the DIY’er ... the potential damage you could cause is not easily fixed.

It would have been better to have done a “zero alkalinity” treatment prior to draining all the old water. You would have gotten a much more controlled etch of the surface. But now that you’ve drained it, you don’t want to do that with a fresh fill or else you’ll load the water up with calcium hardness again.

I would just leave it alone and refill at this point. Then keep your CSI negative as Marty suggests.

 

[BenB]

Thanks folks and apologies for the brief initial message, it was hastily tapped out in the parking lot while taking the little one out for our weekly Sunday Costco run! But time was of the essence to get the question out there in case I'd missed a magic bean solution.

I had previously looked at the zero TA method and it was tempting but the main thread and many others on the subject never really fully recommend it. For the same reasons as an acid wash - long term burning away of plaster and not just the stuff you don't want to, plus general shortening of the plaster lifespan. Also "how acidic" and "how long" seem to be judgment calls.

But the real reason is that I had planned to wait a little longer for the drain but the solar company called on Friday asking if they can bring forward the install of our pool solar system by 2 weeks... and I really didn't want to send super high CH and salt water through those tiny tubes, or have to temporarily put the pool back out of service once they've gone, so this weekend became a very quick drain and refill exercise.

The spot cleaning went "ok" in that I was able to reduce the nodules so they aren't scratchy under foot, but the pumice and little squirts of acid did leave obvious patches around them. The pumice I have is super soft, even with acid it did basically nothing on the tile line and grout.

I think I'm going to need to come to terms with cosmetics not being absolutely perfect. And will consider running CSI on the very low end for a long period to see if we can tease some of that calcium off the surfaces I should count my blessings that it went ok and that the plaster surface is generally smooth and didn't freak out being exposed.

Hope you all had a good weekend and thanks again for jumping into my thread at no notice.

 

[onBalance]

If your plaster surface is smooth, then perhaps the whitish discoloration is not scale, but rather a somewhat porous surface.
Did any of the spot acid treatments restore the original dark gray color? If not, then any kind of acid treatment would only make the surface worse. If that is the case, then just accept the cosmetics and stay the course of balanced water.

 

[BenB]

Woah I've got the trifecta of experts in this thread! I'm honored

Yes - the spot treatments revealed a darker blue/grey underneath.

I'm going to see where the water ends up after the chemicals settle in over the next couple of days and come up with a longer term plan, but for now I'm going to consider this a reasonably successful first 'major pool project' and call it a day!

 

[BenB]

Wanted to just wrap this thread up with a HUGE thank you to @onBalance who took time out of his vacation to stop by my place and look at the pool. I'm very very lucky.

Interestingly, he noted that what I'm seeing isn't scale at all - just uneven discoloration due to age and a previous acid wash. I was very interested to hear that because until that point I'd been planning on running my CSI very low to over time try to reduce the scale, but since it's not scale in the first place I'd do better to just keep it balanced. Also since it wasn't scale, the zero-TA method probably wouldn't have achieved a lot of benefit either.

On the floor of the pool, however, he confirmed I have lots of mini calcium nodules which was slightly unusual in that there were a large number of them, but they were all small and nothing to get concerned about. His tip for those was to use wet/dry sandpaper instead of pumice and acid. I'll grab a few sheets when it warms up a bit and go snorkeling on the last few patches I couldn't get to

So thank you again and maybe this will be of interest to somebody down the road.

 

[onBalance]

Prior to Ben moving into this home, this pool had been acid washed. Perhaps it had some calcium scale that they wanted to remove. Also, this is a dark color plaster job, and as such, it will eventually mottle with some whitening effect over time.
The small calcium nodules issue indicates a bonding problem, and could have also been contributed by the draining of the pool to perform the acid wash, which at that time, the pool could have been left dry for a period of time and which can lead to some shrinkage and then resulting in losing the bond to the old substrate. But again, they were very small nodules indicating a very minor and small bonding area loss. This pool is also beyond the warranty period.

 

[JoyfulNoise]

It’s really amazing how the pool industry uses acid wash as their go-to “fix” for every plaster issue when it’s so obvious how destructive it can be. Ask any of these contractors if they’d acid wash their expensive concrete driveways on a lark just to fix some staining and watch how quickly they’ll quiet down. Acid washing should really be discarded and major plaster manufacturers like PebbleTec, SGM, and others should ban its use by voiding warranties. It’s really almost never a good idea to acid wash any cementitious structure.

 

[onBalance]

I agree Matt. Many in the pool industry do not understand that most acid treatments don't help or solve the problem, and often just make the problem worse. Acid treatments are not similar to washing the paint finish of a car; acid dissolves a plaster finish. Very light acid washes should only be performed when they are really beneficial, not as an excuse to pass the buck. There are better alternatives and solutions to many of these situations, such as sanding.