We have a 1938 stone chimney (not brick) that is severely deteriorated. We are going to repair the mortar immediately and put a cap on top, but we're unsure about weatherproofing the stone. We do want to prevent this deterioration in the future.
One company suggested spraying on an exterior silicone sealant that will prevent moisture and water to pass through the stone.
Another suggested applying a waterproofing chemical that still allows the moisture to pass through so that the stone can breathe. They said that sealants are not ideal because they don't allow moisture to escape and the stone the breathe.
Which method is the best and why?