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QUESTION
Removing Grout Haze - I have a question about cleaning dry grout from the surface of flagstone used on a patio surface. The place that sold me the flagstone suggested using a laundry detergent and a wire brush and scrubbing. I could be out there for days doing that as the patio is approximately 20 x 30 feet. Is there another way to get the excess grout and haze off of the surface? It has dried but I am hoping that you may have a solution. How about muratic acid???ANSWER
ANSWER - The easiest way to remove a cement film off flagstone or tile is using an acid if done correctly. If there is thick excess grout on the flagstone then that should be scraped off first.Muriatic acid is very dangerous and can end up burning the grout stain into the stone that becomes permanent if you are not careful. The muriactic acid has to be substantially diluted if it is used. Sulphamic acid is less corrosive and recommended for this type of cleaning but will take more effort to clean it. If the haze is light enough you can use cheese cloth to remove the haze or if more difficult then use diluted vinegar with cheese cloth and then buff dry.
Make sure you don’t seal the flagstone before you get it completely clean or you may seal in the grout haze.
When using acid it is important to saturate the surface of the stone or tile with water so the acid doesn't tend to penetrate into the stone. After you apply the acid and scrub with a nylon type of bristle brush then it is very important that you flush the surface of the stone with enough water to remove any acid residuals.
After cleaning the stone and letting it dry thoroughly then apply a penetrating sealer either an enhancing type to bring out the colors or the standard type that will not change the look of the stone. Good Luck!
4 thoughts on “How to clean dry grout from flagstone used on a patio surface?”
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What will clean grout out of pavers? I tried the muriatic acid want do one thing there has got to be something out there to clean them. The grout has been in there for 30 years.
Please help!!!
I assume you mean that after grouting the pavers some of the grout residue is on the tile surface and not that a large mass of grout is on the paver surface.
You should never use muriatic acid to clean pavers as it can do more damage by etching the tile that can’t be repaired.
A store bought grout haze cleaner should be used or a diluted vinegar solution. Always saturate the tile and grout with water first before applying the acidic cleaner and rinse afterwards with clean water.
If in fact there was a grout haze on the paver surface the acid should remove it. Or maybe you etched the surface by using muriatic acid? Some grouts are polymer modified and can leave a latex haze on the grout that acid will not remove. There are store bought latex haze removers that you can experiment with. You have to experiment to determine what is the condition in order to determine how to remediate it.
Grout was mistakenly put on top of concrete (in between flag stone). It ruined everything. I need to try a solvent for the grout that will dissolve it and not effect the flag stone. A grout haze has spread all over the flag stone. I need a solvent that can penetrate the stone a little bit. What would you recommend? Thanks
Grout is normally a cementitious material. There is no solvent for cement per se. Acid does attack the cementitious material buy it is only good for removing a haze, but you have to be careful because the wrong type of acid at the wrong concentration can damage the tile and adjacent materials. Never use muriatic acid like what you add to a pool as it is too corrosive and can etch materials.
It is normal to use cementitious grouts the grout joints between the flagstones. Assuming your problem is to remove the grout haze or residuals from the surface of the tile, I would buy a diluted phosphoric acid that is sold diluted for that purchase. Depending on what kind of flagstone you have (flagstone is a shape and can be any number of geological types of natural stone) depends on what to use to clean it and how you clean it.
If the stone is durable enough, I would rinse the stone down first to saturate it. Then pour some of the diluted phosphoric acid over it and get a stiff brush on an extended handle and scrub the tile. Let the tile sit for about 10 minutes and scrub again. If you can safely wash down the tile with clean water or get a wet vacuum and pick up the dirty water. Then rinse the tile again to flush out all of the acid. Be sure to test this process out on one tile out of the way to make sure you are satisfied with the results before proceeding.