I was going to say Sandstone isn't acid sensitive, but Brick acid will eat through anything. You could try grinding it but to be honest I would agree with Jacob. It probably needs changing, Brick acid should never be used far too harsh and dangerous.
I would take a different approach.
If not to far, take a look at it.
Try to ascertain the depth of damage etc.
If light enough, pmt up front to do paid for sample. If terrible, walk. Diamond pads.
Set expectations throughout.
If no good you've lost nothing and covered your time.
If alls well and to customers satisfaction charge premium price as everyone else walked before looked.