Sealing soft stone windowsill

[adamr7747]

Hi All,

I've just discovered that what I thought was a concrete windowsill is actually stonework, covered with a kind of render. The stone is blue lias, which is pretty soft & flakes & deteriorates in exposed locations (where this is), which I suspect is why someone covered it up. However, if possible, I'd like to remove the rest of the render & seal/treat the stonework instead of covering it up again. Any recommendations? How do I make it waterproof? I can repoint the joints, but how do I prevent water collecting on the stonework?

Thanks,
Adam

 

[Bullet-Proof_Biscuit]

First thought is the render is retaining moisture in the stone causing the flaking.. My suggestion would be limewash or similar breathable coating to allow moisture to escape rather than build up and damage the stone. Is the existing render cementous by any chance?

 

[adamr7747]

Thanks. Yep, cement render. Perhaps it was just put on for cosmetic reasons. I'll take it off, clean up the stonework and see what happens...