I have 1/2 inch unlevel plywood floors, need help [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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04-02-2011, 10:52 AM
I am in the process of putting 13" porcelain tile in a kitchen/foyer. The floor was built poorly with several areas where the joists are not crowned in the same orientation. the resulting subfloor is " wavy" 1/2 inch variation over a 6' span across joists in several areas. in addition, the 3/4 subfloor has a 3/8" plywood underlayment (semi glued not adhering) and screwed every 8-12 inches that is very squeaky. i attempted to jack up the joists from the exposed basement and found that the rim joist is also partially to blame (tough to correct). the cabinets are set directly on the sub floor in the most serious sagging area >1/4" over 3 joists. Lastly, i removed the resilient flooring and the 1/8" inch underlayment it was glued to (awful, but installed for the thread reason) so i have to install 1/8" TBD to meet the existing foyer height which is in better shape and will also be the same tile. the tile is here and my brother and brother in law are coming this weekend for the tile party. we are intending to bolster all areas with Ditra as additional underlayment. Geoff

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04-02-2011, 11:00 AM
Some self leveler (SLC) may be an option if you are confident using it in a large area.

Different manufacturers have different requirements, but you should be able to find one you can pour over your 3/4" ply, and then lay your ditra on that.

I would tear up that 3/8 ply and make sure the 3/4 has no squeaks first.

04-02-2011, 02:44 PM
Lets back up just a bit.

Have you verified whether the floor joists will support a tile floor? Plug your numbers into the "Deflecto" in the blue bar above and tell us what you get AND what your joist spacing is.

Also, if you can see the joists from below, look closely at those that appear to be crowned down. Are any of them cracked or broken? Any big knots? If yes to any of these Q's, you may need to sister some new joists in there... :)