Cleaning mortar residue off of stone


Old 06-20-06, 06:41 PM
Thread Starter
Join Date: Feb 2006
Location: Philly
Posts: 82
Cleaning mortar residue off of stone

I am wrapping up a field stone patio and some of the rocks have a thin coating of mortar that I failed to wipe off before it dried. In effect, they just look dusty, but it is really on there. Still, it is such a thin layer that when the rocks are wet they look perfect. I was told muratic acid would stain the stone and I don't want that! The stone is a mix of grey and lilac "Pennsylvania Field Stone" Got it here in PA - this place is AWESOME! 60 acres of every kind of stone you could dream of!

Any way, what kind of product could I use to remove this and not mess with the mortar between the stones? This company, Prosoco (see link below) seems to have all kinds of stuff, but I have no idea which product I need.
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Old 06-21-06, 12:17 PM
Join Date: Jul 2002
Location: Ca
Posts: 746
For Arizona flagstone I use Vanatrol but some like the 600 cleaner. You may want to ask the rockery where you got or test it first because some stones can react with the cleaner and change color. I would also get an acid clean neutralizer just to be on the safe side (necessary if you intend to seal the stone but a good idea regardless).

Muratic acid is the low tech way to do it and it's often stronger than necessary.
Old 06-21-06, 02:35 PM
Thread Starter
Join Date: Feb 2006
Location: Philly
Posts: 82
Hi Alex,

Thanks for the advice! You know, right after I posted I said to myself, "Duh, call the stone place and ask them." I will see what they say, but if they seem unsure, your recommendations should work out fine.

Thanks again!
Old 06-21-06, 02:44 PM
Join Date: Mar 2006
Location: Austin, TX
Posts: 1,405
As a rule, use Vanatrol on white to brown, 600 on red to orange. Be sure to throughly saturate the surface with water before you start, as well as cover/wet everything around it, and follow the dilution ratios carefully.
Old 12-02-13, 12:19 AM
Join Date: Dec 2013
Posts: 1
Sulfamic Acid

I installed a small stone waterfall with river stone and mortar (probably sand stone). In the process, I smeared mortar all over the stone (it was my first time using mortar).

I tried to wash the mortar off the stones with a scrub brush shortly after it was applied but I got so much water all over my mortar, I think I ended up increasing the moisture content significantly, thereby weakening the mortar and increasing it's porosity. So I added more mortar and smeared more mortar all over the stones.

There was mortar reside / haze all over the stones. After a 2 week break, I returned to the job and tried scrub brushing it off but it didn't work. Then I read every internet article I could find on the topic but couldn't get a clear answer on what to do. Then I went to Home Depot for some acid and they only had 2 types, muriatic acid and sulfamic acid. I chose the sulfamic acid because I read that muriatic acid is dangerous.

I added the sulfamic acid to a bucket of water, following the instructions on the container. Then using a scrub brush and rubber gloves, I scrubbed the acid onto every stone that had the haze (which took about 5 minutes). Then I immediately washed it off with a hose because I was afraid it might discolor my stones if left there too long. I let it dry (helped it dry with a blower). The haze was mostly gone. I repeated the procedure in a couple areas that needed it and now the mortar residue pretty much completely gone. It doesn't look like my mortar joints were damaged.

Hope this helps someone.

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