What's the best way of cleaning sandstone? I've just had large sandstone terrace laid and the builders have left gobs of cement/paint from the roof/ bits of wood shaving which have ingressed into the sandstone. I live in SE Asia and getting the builder back to rectify is not an option. They bodgit and scarper in the finest tradition :-) The quarry from where we bought the stones say you really shouldn't use acid but in this case do I have any other option? The material is 600x600x25 slabs. Tx for any help.