waterproofing travertine? Help!
We have a number of external walls about a metre high, cement rendered on both sides and made of tufo blocks. Sadly the rendering keeps getting spalled off after the winter due to, I think water in the walls freezing and expanding. Iam thinking of sealing the joint between walls and terrace with silicone rubber and what I think may be the main problem - a one and a half inch thixk capping stone complete with drip groove but having joints about every four feet and which I strongly suspect is porous, coupled with the fact that this is flat is allowing water to penetrate to the tufo underneath which we all know is like blotting paper. Can you get some kind of solution which will make the travertino waterproof? (possibly silicone based? )