Concrete Or Mortar On Plywood - Flooring - DIY Chatroom - DIY Home ...

Actually, not at all. We don't install flooring. We install the electric (low voltage or line) radiant system that is integral. The design is up to someone else but in all of the installations where we have installed a cable (exclusively), solidly 1/2 are on plywood and the rest is on concrete/backer or some other type where a mortar, thinset or SLC is applied after we're in place. My apprehension came in when a roofing tar paper was being asked to go in before us.

Then, backer board was suggested instead and what I couldn't understand is what's the difference between backer board and the mortar or concrete itself. I "thought" that if you use a mortar or concrete over BB, the moisture will surely wick through to the plywood below...and doesn't Durock require a thinset under it to maintain their warranty...or is that old info?

So, I was back at, if that was the case, why not just apply the mortar right on the plywood!? I do understand that if you wet the plywood over long periods it will damage the wood, naturally. But I have been in many new construction homes where the plywood sub is open to the elements for long periods, getting wet or snowed on...It dries out, no? So, what's the difference???

Keep in mind that I'm here seeking information about something I'm not sure I understand. I am not looking to lay blame.

Source: http://www.diychatroom.com/f5/concrete-mortar-plywood-108549/

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