Need advice on mortar repair

[GDN]

Just to be up front, I got too aggressive with the acid earlier this summer. We have one main spot on the hot tub that seems to have scale - assumed to be calcium. It's almost like it just pours out of this one spot and runs down the side and leaves a white mess. We don't have a problem anywhere else in the pool, although the PH continues to go up and we add 8 to 12 oz of acid once to twice a week.

To say the least, to clean this, off acid worked well, it fizzled and bubbled and then washed away. The problem is I didn't dilute much in my spray bottle and it was a couple of weeks before I realized how well it was really working (and the damage I had done).

Do I need to take action or is there still enough mortar and grout in place around these stones and tile? The tile is still very secure, nothing loose. I know the tile was put on with a thin set or mastic and then the stone I guess just likely mortared in place. The pool is 5 years old.

First pic is a wide shot and then a few more close up around the stone and tile where. If anything is needed and if so what product is best to patch and will will it ever match or look like a big disaster if I do try a fix? I appreciate all of the advice, a lot of very knowledgable people here.

Also easy to see I need to so some more cleaning, however with a much more diluted solution of acid.

 

[YippeeSkippy]

What you have is efflorescence. Hit up the search bar above and use the G option, and you'll find a lot of past posts about this problem.
Basically its moisture behind the stone pushing calcium and salts forward, like a leak, but once the water evaporates the salts are left behind.

Maddie

 

[Dirk]

This is what I was taught by my stone-guru. I'll rely on our chemists here to correct me if need be. If we can use the term "strength" to describe the affect an acidic solution has on your stone and grout, then you would adjust the strength of the acid using an alkaline substance to raise its pH (to weaken it), not just dilute with water, which doesn't actually reduce its strength, only changes the amount of acid in contact with the stone. Which is not the same thing. What he does: he starts with acid and mixes in the alkaline and tests the pH of the resulting solution until its strength is what he wants to start with (he uses strips for that). He then applies that to an inconspicuous area with the problem stain, to see if the solution is strong enough to remove the stain. If not, he adds an amount of acid to the solution, and repeats this process until the solution has the desired affect. And he is very careful in how he applies the solution, and how he quickly neutralizes it after it's done its work, again with the alkaline and not by just rinsing with water. That's the gist of it. This process minimizes damage to the surrounding areas because it utilizes only the acid strength that is required, and doesn't blast the surface, both that with the stain and without, indiscriminately. This requires a level of patience and skill few possess, which is why he's considered to be one of the top experts in his field (cleaning, restoring, re-coloring stone, etc). But perhaps you can at least approximate his methods the next time, as you now know the consequences otherwise. I don't know the best alkaline substance to use for this purpose, but I could ask him if you're interested.

 

[GDN]

Thanks for the feedback on the issue. It looks like I worked on it with the right product, which is acid, but I definitely need to dilute and I need to neutralize after. I did only rinse with water.

If anyone else has advice, I obviously need to do a little more cleaning, but more so I need to understand if I've got any repair here and the right product.

I also understand there is likely a source of water behind there and that could be leaking in from the cap perhaps. The pool company was a pain in the Rear at the end of the build, not sure I even want to deal with them, although if there is a problem I should still see if it could be rectified.

 

[Dirk]

Just to be clear, I didn't necessarily condone the use of acid for this, though I suspect that is the right product. My "guru" has an arsenal of products, and he always starts his pre-cleaning testing with the least harmful one, then works his way up the "power scale" of products until he finds the one that does the job, including acid if that's what it takes. He uses this MO, only applying the least that is needed, and only after testing it first, to avoid the result you encountered. I don't know what those other "magic potients" are, some of which are his own concoctions. It really is an art. The cleaning is easy, it's protecting the remaining stone that is the hard part.

 

[JoyfulNoise]

1. PPE's!!! Always wear PPE's (eye protection and either latex or nitrile gloves)
2. Stiff nylon or tampico brush that you can lock onto the end of a cordless drill (brass bristles can be used too but stay away from steel wire)
3. A diluted solution of acid (diluting with water has the same effect in lowering pH as adding a base, so there's really no difference). You can try cleaning vinegar first and then go up to muriatic acid if need be. There are also commercial efflorescence and scale removers that will work, just follow the label instructions. Believe it or not, toilet bowl scale remover (the blue kind that has hydrochloric acid in it) works well because they add a thickening agent and other chelating agents. Toilet bowl cleaner will cause a little foaminess in the water so use it sparingly. The foam will go away.
4. Lots and lots of elbow grease.
5. Neutralize with a solution of baking soda and water

You start with the least aggressive means of cleaning and work your way up. If your cleaning the grout between the stones or the tile, use a small piece of pumice stone that is sized to fit the grout line. Do not use pumice on tile surfaces as it can scratch the tile glaze. Only use pumice on stone surfaces if the texture will not be harmed.

 

[Dirk]

Baking soda, of course. Duh, I should know that! Thanks Matt.

 

[GDN]

Thank you for the continued replies. This gives me options for cleaning and gets me on the right path. I had wondered if the baking soda wouldn't neutralize, thanks for the confirmation. I will be more gentle on cleaning, but it had gotten really bad over the winter. We do have pumice stones and used those to make some headway. It was close to 1/8" thick in places. Once I saw what the acid would do to it I just got too aggressive, and didn't neutralize after it had done its job.

So while I need to do some more cleaning while it is still warm enough to do so, I'm wondering if there is enough damage that I need to work some mortar back in around the stones and around the top of the tile? Any thoughts on that?

 

[Dirk]

Sorry, not from me. It's probably a simple thing, with a trick to get it to adhere well.