We hired a contractor to redo our master bath and are now involved in a dispute. Mostly due to him using regular sheetrock with redguard waterproofing membrane over it in our shower... our community adheres to the 2006 IBC and we KNOW this is against code and that the manufacturer of redguard doesn't recommend their product used in this manner. He is still twisting the language to say he is correct in using these products. Is there anyplace that it's written by experts that this is NOT the way you build a shower to last? Thanks!