In regards to setting tile on top of plywood, what type of waterproofing membrane needs to go between the plywood and the durock. This is not exterior grade plywood, its just regular 3/4″ OSB plywood. Is 15 lb felt paper stappled to the plywood okay? If I put something between the plywood and the durock, how will the thinset be able to do its job of securing the durock to the sub floor? Any tips would be helpful.
Thanks,
Mike
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Replies
guess it depends on why ya want it waterproof?
and are we talking walls ...or floors.....and god forbid..a shower floor???
and while we're at it...why isn't this ext grade ply?
Jeff
Buck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
I am putting ceramic tile down on the floor in a bathroom. The subfloor is 3/4" plywood. Do I need to lay down 15 lb felt so that the plywood does not get ruined from the moisture in the thinset? It is an existing floor and the 3/4" plywood was already there. Should I remove the plywood and put new exterior grade plywood down?
Not to be a wiseguy, but OSB, as mentioned in your first post, is not plywood. It is oriented strand board which is a blend of wood chips and exterior glue. Plywood is a sandwich of sliced wood veneers glued together, sometimes with exterior glue. 99 % of the time, subfloor materials use exterior rated glues. Having said all of this, do not put felt on top of the subfloor. Thinset directly to the subfloor, and then install your backer board.
carpenter in transition
Edited 9/9/2003 7:13:06 PM ET by TIM_KLINE
OSB is not plywood. rg
None.
I would, however, put unmodified thinset under the durock and nail the durrock to the ply, not the joists. Use modified thinset for the tile.
If it is OSB, check the manufacturer of the CBU. Some do not allow tile to that substrate, and you may have to skin it with real EGP plywood. One manufacturer who I thinks warrants over OSB is Schulter and the CBU is Ditra. But double check their website. It is actually not a CBU per se but a wierd plastic type membrane over which the tile is laid.
Good stuff.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Follow up question regarding durock over plywood.
I'm remodeling our second bath/laundry room, which had vinyl glued to the subfloor with mastic, and plan on laying new 13x13 ceramic tiles. How important is it to remove all of the old mastic from the plywood before applying thinset and laying the durock and then nailing/screwing? I have about 50% of the old mastic removed with limited gouges to the plywood. Any suggested techniques would be appreciated.
Thanks...
I don't live in a perfect world either. 50% is not ideal but a comprimise you'll be able to live with - as long as you use a modified thinset AND screw the CBU's to the floor.
As someone mentioned earlier, one of the roles of the thinset is to create a fully supported base.
I am assuming the 50% mastic coverage is not all in one area.
Frankie
Not very important.
The thinset does nothing except act as a cushion for the CBU. It does not bond to the plywood and can go right over the vinyl and mastic. We call that stuff "cutback" by the way.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934