yet another question about vapor barriers
My contractor is using hardibacker 500 and was not going to use any kind of vapor barrier. I talked to him about putting poly behind the hardibacker or kerdi or other waterproofing on top. He prefers to tile directly on the hardibacker, so we decided on poly. However, he had some questions I could not answer:
1) Is it okay to have sheetrock, poly, hardibacker and then then thinset and tile?
2) Will putting poly behind the hardibacker negate the hardibacker guarantee since their installation instructions do not specify any kind of vapor barrier.
3) Can he use Tyvek or 15lb felt instead of poly?
4) What is poly? What exactly do you buy from Home Depot when everyone is talking about "poly"?