Dave Osborne wrote:
John Rumm wrote:
On 10/09/2010 12:04, Dave Osborne wrote:
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?

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!

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.