Subfloor thickness for tile?


Old 11-22-18, 02:20 PM
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Subfloor thickness for tile?

I am remodeling my half bath and there is 5/8" plywood subfloor over 7 1/2" joists that are 16" on center. The bath is small - 3' x 5' floor area so the longest joist run is 5'. I am going to install 9" x 9" porcelain tiles. I bought hardiebacker ez grid 1/4" thick cement board and the instructions say that there should be a minimum of 5/8" plywood underneath. I have read websites saying that 1 1/4" total subfloor thicknes is generally recommeneded. Should I add another 3/8" layer of plywood over my 5/8" plwyood?

Would another option be to put 2 layers of the ez grid 1/4" cement board over the existing 5/8" plywood. All things being equal, I would rather go with plywood as it seems easier to work with and less dusty when cutting.

I bought premixed thinset - Mapei type 1 tile adhesive and wondering if this was a good choice for underneath the subfloor and tile? I read a few forum posts about premixed thinset not being as strong as powedered? Thank you!

Old 11-23-18, 12:35 PM
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1/4 CBU is for counter tops go with the 1/2"

I know everybody says CBU is not structural but when it's screwed down with twinset it definitely adds some stiffness.

And dont use that pre mixed krap, get a good brand of tile mortar!
Old 11-23-18, 01:01 PM
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1/2' cement board is for walls not floors. 3/8" plywood will add nothing to the strength of the floor.

5/8" + 1/2" ply minimum, thinset (from powder), 1/4" hardie screwed down and then thinset (from powder) and finally your tile. Make sure you use the correct hardie screws.

Anything that can sit in a tub and not harden for years is not something you want to use. It is very easy to mix small batches of thinset as you go. Need water a bucket and a trowel. I use a cement trough that you can get for around $6 in the cement tool area of the big box stores.
Old 11-23-18, 09:50 PM
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I bought premixed thinset
No such thing. Thinset is a cement-based compound and starts to cure as soon as it encounters water, Anything premixed is mastic, not thinset.
Old 12-15-18, 02:27 PM
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Im not a professional tiler but ive tiled many floors and have never ever had a tile crack or pop, even in rental properties.

I would use a min 1/2 plywood on top of the 5/8 ply. This is a small area and floor deflection shojld be almost zero.

Use 3 inch wood screws thru both sheets of plywood and into the joists. Fill any gaps or depressions in the 5/8 ply with liquid nails as you lay the 1/2 ply on top. Make certain the plywood joints of both layers are at 90 degrees to each other.

I do not use cement board or hardie board on floors. I use the wire mesh, staple it, scratch coat it with the same high quality thinset that I use to set the tiles.
Old 12-15-18, 02:30 PM
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I should add that I ONLY use 10mm poreclain tiles on floors. They are much stronger than ceramic tiles.

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