Sawn Indian Sandstone cement stains

[dave1975]

I've just laid a new patio using sawn sandstone. I pointed it using a semi wet mix (3 to 1) and brushed away any excess as it was drying. On previous patios, i'd leave it a week and then give it a final clean up with the jetwash although this time its hardly touched it. This time its stained it and I cant seem to shift it. Any one got any ideas. Thanks

 

[lostinthelight]

Ive used weak brick acid on red sandstone walls but dont know if it would be ok for your stone. You could test on an offcut I suppose? Staining aside, did you consider extending the grass so there is not a thin strip of sandstone to kick loose as they often do near an edge?
litl

 

[dave1975]

I've just heard of too many horror stories of people using acid so am just a bit wary of using it.
I'm going to cut more of the grass away to create a bed so the thin strip shouldn't be an issue

 

[r896neo]

That is a right mess. The issue you have had is to do with the soft stone. Is it fossil mint or similar? The very soft sandstones when sawn are so porous that if you dont wash stains right off they can get drawn into the flags.

Shifting it will require chemicals of some sort.

Normal mortar acid could be problematic but may be fine, most sandstones its ok but the odd one it all goes to hell.

There are a couple of other cleaning agents suitable, perhaps post on the paving expert 'brew cabin' forum

 

[dave1975]

Yes it's called mint although they are actually cream and buff coloured. I'll route out the other forum in the morning. Thanks

 

[geraldthehamster]

I had this issue with Indian sandstone, some of which was reddish. I removed the cement residue effectively with brick acid, but some of the stone went vividly red because of reaction with the iron in it. After a couple of years this had faded away and now it's fine.

My neighbour built a patio with a mixture of old sandstone and new Indian sandstone. Same issue. He left his alone, and after a winter and a summer the staining had pretty much disappeared.

Hope some of the helps.

Cheers
Richard