I'm going to be using the Kerdi shower pan and membrane to seal a steam shower. I understand the process of installing the membrane, deck and preparing the wall and ceiling substrate.
This question is specifically about the subfloor.
Do I need to apply a waterproofer such as Redgard to the subfloor ply before I apply the thinset to set the Kerdi shower pan?
The same answer, I presume, is applicable to a dry pack pan as well?
Best Answer
No I would not apply water proofer to the subfloor under the shower pan (unless we are going to be waterproofing the entire floor it might be easier to just continue it under the shower pan).
I think The Evil Greebo does bring up a good point, because this is a steam shower I would be even more concerned about mold developing in this humid environment. IMHO, if you will be tiling the floor I would put a water proof membrane under the entire floor and not worry about using pressure treated wood for the subfloor. If you use the DITRA and cover the seems that should be waterproof so there really should not be moisture getting to the subfloor.
Of course the (relatively) small increase in price for treated plywood may be worth the peace of mind (are be a backup if water makes it through the floor's water proofer.