Remove mortar stains Indian sandstone

[bettz1]

Hi any advice on what I could use to remove a few mortar stains from the edges of Indian sandstone kandla grey?

I bought some bostik mortar remover which a few people recommended watered down but noticed it says not to use on sandstone

Any idea?

 

[Mike13]

Three choices:
Scrub with a white silica sand, a few handfuls and a stiff brush, you will be there quite a while...
hydrochloric acid
Oxalic acid
The second two are much quicker, if you do it with a small brush a little at a time you can wash well to stop any continuing reaction when it looks good enough.
Try a bit on an ofcut of the sandstone, the chalk/lime content should be low enough that it wont discolour.

 

[Anthony B]

Three choices:
Scrub with a white silica sand, a few handfuls and a stiff brush, you will be there quite a while...
hydrochloric acid
Oxalic acid
The second two are much quicker, if you do it with a small brush a little at a time you can wash well to stop any continuing reaction when it looks good enough.
Try a bit on an ofcut of the sandstone, the chalk/lime content should be low enough that it wont discolour.

Ive got a few off cuts so was going to try a watered down solution of bostik mortar & Brick cleaner