i he has a vapor barrier behind the sheetrock he has effectively created a vapor trap.1 membrane is all thats needed.Generally there is a vapor barrier on any outside wall of a house.Inside shower walls should have a vapor barrier.
Self Stick Membrane like which product,Flextherm??
Flextherm is a good product for what it was designed for.It was designed as an antifracture membrane with the ability to bridge cracks in concrete floors for the effective installation of Tile.
The only flaw in his theory(and believe me this is Tile Theory and has no basis in TCA standards that I am aware of)is the existing vapor barrier problem. if there is no existing vapor barrier i dont see a problem with the theory except that it makes for an awfully expensive vapor barrier.
If he wants waterproof,have him put up his concrete board and paint it with Pro Red Or Custums Redgaurd waterproofing Membrane.This is at least a more common and known product that has actually been in use and is being spec'd by architects.
Schluter Kerdi would be another option...........Perhaps he should come into the Pro Hangout and Visit us.We dont bite
