# How do I get grout stains out of flagstone?



## Firenutz (Oct 3, 2009)

e. Overall it came out pretty good. I used 1-1/2" thick Pennsylvania bluestone which is basically flagstone. It has a rough texture. I used a premixed sanded grout for the seams and I made a mess of it. It was pretty hard to get all of it off the rough texture. It's been dried on there a year now and it really bugs me. Is there a way I can get rid of the grout staining? You can see the light gray discoloration in these pics.




	

		
			
		

		
	
img]http://i457.photobucket.com/albums/qq299/jeremyk77/512MBmemstick941.jpg[/img]


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## Ncountry (Oct 3, 2009)

I am not a tile expert, but I have used muriatic acid with success in the past.  Had to use this when I discovered marble (white) is porous and black grout makes quite a mess. :sick:


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## Corey (Oct 3, 2009)

That is what I had to use, too - muriatic acid (really hydrochloric acid, though if you ask for hydrochloric they usually think you're making drugs)  Depending on the strength (37% is about as high as you can get and usually puts on quite a fume show when you pop the top) you may want to dilute it some.  If it's the full 37%, you might try mixing it with 4 parts water for starters.

What I wound up doing:  wear gloves and goggles, mix up the acid - weak for starters, stronger if you need it,  mix up a 'neutralization solution' of several tablespoons of baking soda in a gallon of water, and draw up a gallon of fresh water for a final rinse.

Apply the acid mix to the stain in a little pool if possible.  You should see it start to bubble and fizz on the grout.  Use a nylon bristle brush...toothbrush if the stains are pretty small...to work the acid around and scrape off any grout stain which is beginning to disintegrate.  Keep doing this until the stain is gone or the fizzing stops (all acid has reacted).  Blot up the acid with paper towels and put immediately in the trash.  Wet a towel with the baking soda water mix and swab the area to neutralize any remaining acid.  Finally wet a towel with fresh water and blot the area to remove any baking soda then dry.

Definitely wear gloves and glasses for protection and you may want to try this on a scrap of stone if you have it, or an inconspicuous place to make sure the acid doesn't react with the stone - it shouldn't, but you never know!

I went through this on my porcelain floor and it did fine - tried all sorts of stuff before...lime-away, vinegar, hard scrubbing, oxalic acid, tile haze remover, etc - but in the end, it came down to good ol HCl.


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## Panhandler (Oct 3, 2009)

I work with HCL everyday. One thing I didn't see mentioned, be very sure to have plenty of ventilation. You don't want to get a good breath of that stuff. I'd use a box fan to pull fumes away and every window open you can.


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## devinsdad (Oct 3, 2009)

here is a site that might help  http://www.findstone.com/curegen.htm


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## m0jumb0 (Oct 3, 2009)

not trying to threadjack here, but will HCL damage gelcoat on a fiberglass shower?  I have some grout blobs that dried in a couple places that I'd like to remove


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## Dune (Oct 4, 2009)

One thing I didn't see mentioned, in rhyme form so it is easy to remember; Always do what you oughta, pour acid into water.

Pouring water into acid can get very exiting. Don't do it. Pour acid into water.


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## Corey (Oct 4, 2009)

m0jumbO - a mild solution of HCl should not damage the gell coat - though as always, try it in an inconspicuous place to be sure.  Though if it's an actual blob, I would be surprised if a little sideways pressure with a plastic putty knife or something similar wouldn't cause the blob to pop off.  It can take quite a while for the acid to eat through a complete blob.

Dune - you are very correct.  I didn't mention it because HCl doesn't get much stronger than ~37% - (it's actually hydrogen chloride gas dissolved in water and 37% is about the limit)  Consequently it's already 63% water and adding a little more doesn't change things much which ever way you go.  Though a few drops of water in concentrated sulfuric or nitric acid can sometimes put on a good show - so it's good to get in the proper habit.


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