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Unread 11-08-2004, 07:36 PM   #1
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Join Date: Nov 2004
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how think should my subfloor/underlayment be?

I'm a rookie at this so my questions may seem a little dumb but here goes?

I want to use 1/4" thick 12" ceramic tile in the upstairs and downstairs, approx. 35 sq ft bathrooms (floor space). The upstairs has 3/4" subfloor and 1/4" ply, I plan to throw 1/4" backer and then install tile. Is that enough support. the floor joices are 16" apart. Also, does the backer butt up against the tub, walls, etc or do you leave 1/4" on these like the tiles and use caulking??

2nd room is on flat cement no cracks, already pulled up lino and removed glue. Is their some sort of membrane to put down on the cement floor to prevent movement or cracked tile? If their is i would guess you use thinset on this.
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Unread 11-08-2004, 08:39 PM   #2
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No dumb questions if you have sense enough to axe'em, Chad.

I'm gonna guess you removed some vinyl flooring from the upstairs bath also, and the 1/4 inch material was an underlayment for it. That underlayment needs to be removed also, it just has no place in a tile installation.

Then we'll need to know the size and unsupported span of the floor joists under the 3/4 inch subflooring.

While the 3/4 inch plywood is technically enough for a tile installation with your joist spacing, you won't find many pros hereabouts who will recommend tiling over it without adding another layer of plywood, real plywood, 3/8ths inch minimum.

Never wanna butt CBU tight against anything, always leave a gap, and it's best to leave the size gap recommended by the manufacturer of the CBU you're using.

You can tile directly to that concrete slab with a good modified thinset (which will be more specifically described by big-time tile guys hereabouts) if you're willing to take a small chance on cracking over the years. If you want a guarantee against such cracking, you can use a sheet membrane such as Schluter's Ditra or one of the Noble Company's products.

My opinion; worth price charged.

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