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Gardening with Stone

Question about acid washing flagstone

19 years ago

Can anyone tell me where I can get whatever it is that I would need to acid wash flagstone to remove the "mortar haze" that's on it? (The flagstone is set on a concrete base, with mortar.) How harmful is this stuff going to be to plants in the area? What precautions should I take?

Thanks in advance!

Featured Answer

bambooo

19 years ago

Masons commonly use muriatic acid to wash the mortar haze away. Directions sometimes come on the side of the bottle.
It is a rather impure form of hydrochloric acid. It will kill plants and eat your blue jeans. Gloves and eye protection and a running hose are going to be needed. To minimize damage to surrounding plants cover them with a tarp and flood any runoff with water.

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Comments (6)

Lindsey_CA
Original Author
19 years ago
Thanks! Going to try to take care of it this weekend. :-)
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O boy .....the heavier stuf you are going to have to remove manualy either with a trowel or chissel / scraper, or if it is still soft enough, with a wire brush, this will be time consuming, and try not to leave scrape marks in the stone when you are doing it , then clean with the acid making sure to wet the stone first and rinse thoroughly afterwards.. heavy rubber gloves & eye protection are a must.. When all is completely dry use a grout bag to grout in the joints, experiment with the grout mix usually slightly richer & softer mix (cake icing or dq ice cream consistency) will be best but dont make it sloppy or you will have the same problem. when the mortar is firm to the touch then tool it as you want. Again make certain this is real stone before proceding have fun Martin
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rookielndscpr
19 years ago
never use muratic acid on natural stone! there is a product made by Prosoco called Vanatrol, it is made to soften and remove mortar without bleaching out all the beautiful natural stone colors.

Here is a link that might be useful: Vana Trol link
Marcos1234
12 years ago
Since no one answered your question directly, you can get muriatic acid in any pool supply store. Make sure to read EVERYTHING about it before you play with it. Do a test run in a place where it is not going to be too visible if it turns out to be damaging on the learning curve. Have plenty of protective gear, lock your pets away, have your kids go to grandma's, protect any vegetation that you don't want to end up dead. Have a plastic bristle brush ready to scrub the bubbles off to see the results before you wash it off. It's a lot to think about, but it can be very rewarding if it is done well. I work in the office for a Construction and Maintenance Company here in Los Angeles and based on the hands of the guys that do only this kind of jobs I'd say that those jobs are not for do-it-yourselfers. But by looking at how they do it and how nice and clean concrete surfaces became, I bought the materials and did my own driveway and it turned out to be like new!

Here is a link that might be useful: Look up acid wash on this website.
poppasmurf302
5 years ago
i work with all different types of stone, bricks, pavers, concrete - and using muratic acid to clean natural stone and bricks is 100% safe(for the stone), if done correctly. i usually mix it with warm water at a lower ratio(more diluted then recommended) and it works great with a wire brush or stiff bristle natural fiber dustbrush. i dont know a brick/stone mason that doesnt acid wash every job after setting and pointing.
Carolyn Leahy
4 years ago
It bleached all my stone on my pool waterfall !

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