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I am removing a laminate tile floor. There looks to be 2 layers of 3/4" Plywood as the sub-floor. Do I remove 1 layer of Plywood and install 1/2" concrete board or leave the plywood and install 1/4" concrete board on top of the plywood before installing the porcelain tile floor? My concern is that if I leave the existing sub-floor material I am going to have a ½” rise in the floor from one room to another.

  • This isn't easy to answer. You can probably get rid of one layer and go with cement board but the extra plywood might be needed to provide a solid foundation given joist spacing, load bearing poles in your house and so on. – DMoore Nov 16 '14 at 17:05
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wirelath nailed over the plywood(overlapping the lath 2",use paper backed lath to avoid moisture of setting/grout materials)nail or staple(pneumatic,not a hand staple)in a 8"x8" grid.wire acts as a trampoline,the thinset gets into the mesh but won't twist when the plywood deflects.normal thin-set is fine in the application(unless a modified is needed for the tile).

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Although cement backer board is an ideal substrate for tile, you could bond directly to the existing plywood if it is clean, flat and strong (little or no flex); this is acceptable for areas that see only incidental moisture. There are polymer fortified thin-set mortars specifically designed for direct application to sound plywood flooring that does not exceed maximum deflection specs. I have had very good results, proper application is key. Check it out: fortified thin-set mortar

1/4" cement backer will conform to irregularities in the floor (high/low spots), so if the existing plywood is not smooth and flat I would probably remove the top plywood layer and use 1/2" backer board to give the smoothest flattest surface.

  • I would never do this. Ever. – DMoore Nov 16 '14 at 17:03
  • @DMoore, what would you never do, install tile yourself? Install it per manufacturers directions directly to plywood? Install it on 1/2" cementitious backer board? Successful tile installation depends on numerous factors and requires proper application techniques. I have personally installed tile directly to clean sound plywood with great success, 15 years later it still looks brand new. As stated, maximum substrate deflection must not be exceeded. – Jimmy Fix-it Nov 16 '14 at 17:22
  • Install tile on plywood. You don't know how many homes I have bought with tile on plywood. I can count the number of said tile that wasn't cracked (grout or tile) on zero fingers. – DMoore Nov 17 '14 at 6:59

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