The parents have had a patio laid in Indian sandstone/limestone. Dad decided to try getting a few mortar stains off with acid-based patio cleaner. After a week or so, the patio has turned orangey-brown where the acid has been.
According to paving expert, the acid staining is permanent. :-(
Anybody know if you can get rid of acid staining? Oxalic acid-based scouring powder seems to be an option, but paving expert cites oxalic acid as "unproven". Is it worth a go?
Cheers, DaveyOz
Could try it on one spot and see.
Other options include just leaving it - a bit of weathering will blend it in over time, or acid washing the rest of it to match!
I've ordered some Oxalic acid. We'll see whether or not it works.
If I acid washed the rest it would look like Cotswold stone instead of grey limestone!
Do they like the look of Cotswold stone? ;-)
He or she is probably correct...
: : Anybody know if you can get rid of acid staining?
Sand blasting, removing the stone to below the level of the acid damage - a bit 'kill or curer' though...
If it was sandstone, this happened to me too.
It proved too be a lichen of some sort that lurved the acid conditions.
Try caustic soda or bleach and a pressure wash.
After a while, the acid goes anyway and the more usual greeny brown lichens take over.
sandstone is not damaged by acid.
Take care with oxalic acid - it is poisonous. It is the chemical whic makes rhubarb leaves dangerous.
Malcolm
The first thing I'd try is neutralising with washing soda. Not sure why the acid would have produced a brown colour but the salts of said acid may wash off more easily.
Iron in the sandstone? Maybe we are dealing with rust.
Edgar
From: stuart noble Date: Fri, 10 Sep 2010 Time: 19:42:28
It's the action of the acid on ferrous fragments in the stone. See the para beginning "York Stone" in:
: sandstone is not damaged by acid.
So you are saying that the OP is lying?...
In how much of a hurry are you? I had some Indian sandstone laid (always a mistake: if you want a good job done, do it yourself) by a builder who managed to tread mortar slurry all over the surface, so I cleaned it off with brick acid, and had just the result you describe. Two years on, the excess redness has pretty much weathered away.
Cheers Richard
Thanks for that Richard; it's nice to know it will weather eventually. I tried the pressure washer this evening and it seems to have dulled it down a little. Parents' pressure washer is a bit crap tho'. Will try with a more powerful PW if the Oxalic acid has no effect.
Just to be clear for the pedants, it is in fact limestone, but it is (apparently) sometimes called Indian sandstone.
I cam assure you that all my cheap indian sandstome was washed with brick acid, and no stains resulted. Huge algal blooms did, however.
He never said it was damaged. Merely that it tuned red. Painting it with red paint turns it red as well.
mine washed out with a pressure washer immediataley.
Though it took several weeks to develop after serious rain and only developed where the water laid..
Well if its limestomne why call it sandstone?
Indian sandstone is sandstone. AKA fake York stone. IIRC
So ...
once applied, don't eat the paving stones
: > : > : sandstone is not damaged by acid. : >
: > So you are saying that the OP is lying?... : >
: >
: He never said it was damaged. Merely that it tuned red. Painting it with : red paint turns it red as well. :
It also damages the surface, especially if it is meant to be - err - sandstone coloured - and the paint won't come off.
By your 'logic' acid doesn't damage anything, assuming that the application was intentional, duh! :~(
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