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After grouting about 75 sqft of a 225 sqft quarry tile room we noticed some pretty bad grout haze. I've since learned that with quarry tile it's recommended to seal the tile prior to grouting to help in the clean up and that quarry tile is particularly difficult to clean of grout haze. However, "difficult" doesn't seem to capture the problem. To remove it, so far we've tried:

In all cases, we also vigorously scrubbed with a stiff brush. None of the above have made any noticeable difference. What else can we try? I'm starting to feel that we might have to rip up the hazed tiles. Here's a shot that shows the hazed tiles next to clean ones.

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You were on the right track with vinegar as an acid, but it’s not strong enough.

My quarry tile had the same hazy look as yours. I mixed 1 quart of 37% muriatic acid (hydrochloric acid) with 1 gallon of water, sponged it on, let it work for a few moments then sponged it off several times with a different sponge that had been rinsed in a separate bucket of clean water. I worked in sections. The quarry tile came out perfectly clean.

There was some hissing and bubbling from the grout lines, but the grout wasn’t harmed.

Use adequate ventilation, add the acid to the water (not the other way around), use a plastic bucket, wear splash-proof goggles and rubber gloves. Don’t let the acid solution touch any metal such as doorway thresholds, etc. If you get the acid solution on your skin, rinse promptly with clean water.

Review the MSDS for whatever brand of muriatic acid you choose. The MSDS can usually be found online.

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  • I'm going to run to get some muriatic acid now to give this a try. When you say a few moments, do you mean seconds? Minutes?
    – ecline6
    Commented May 18, 2022 at 14:17
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    @ecline6 From what I recall, the acid dissolves the haze instantly, but I probably let it work for a minute or two for good measure. I didn't leave it on long enough for the solution to disappear into the tile, which would probably take something like 10 minutes.
    – MTA
    Commented May 18, 2022 at 14:26
  • No luck with the muriatic acid over here. Tried in a 4/1 dilution as you suggested as well as a 2/1 dilution. Scrubbed vigorously and left to sit for 10 minutes. Zero change in the haze. Was your quarry tile sealed prior to grouting?
    – ecline6
    Commented May 18, 2022 at 16:59
  • @ecline6 My tile was unsealed and the grout was sanded cementitious grout without any kind of polymer, latex, epoxy or modifiers in it. If your grout contains one of those modifiers, that may explain why it's not dissolving. Also, if you got hold of some of that infamous so-called "green" muriatic acid, it's not full strength 37%. I wouldn't know how to dilute it because they don't list the concentration on the label. If your grout lines are not bubbling, either the grout is resistant to acid because of modifiers or the acid is too dilute. Sorry it didn't work out for you.
    – MTA
    Commented May 18, 2022 at 17:33
  • Looking online, it appears that it's a 20% concentration. So presumably, less dilution should bring it up to strength. I'll try a 1/1 and report back.
    – ecline6
    Commented May 18, 2022 at 17:50
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After trying so many things, what finally made an impact was Mapei™ UltraCare Epoxy Grout Haze Remover. It looks like I may need to do a couple applications, but the haze is coming up. @MTA's suggestion that even a non-epoxy grout may not be affected by an acid product if it has resins in it pointed me down this path.

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