preparing subfloor for bath [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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tom in ohio
01-08-2003, 07:34 PM
My home was built in the 1950's. I want to lay tile in our bathroom. I already removed the hardwood flooring. The subfloor is exposed; it is 3/4" solid t&g which runs at 45 degrees. The floor joists are 2"x12"s on 16" centers.

Someone suggested bracing the floor from underneath, in places where the floor seems to have some give, with 2x4's attached to joists and the subfloor. Then he suggested using a leveler to make for a level surface, spread latex-modified thinset mortar, Ditra, more thinset mortar, and then tile.
The bedroom adjacent to the bath is a new addition and will be carpeted. Will height of the bathroom floor be a concern?

Is there a better way to prepare the floor?

Since it's in the bathroom, should I lay some type of moisture barrier down?

I'd like some good advice.

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John Bridge
01-08-2003, 07:47 PM
Hi Tom, Welcome. :)

The Ditra is a good idea, but only if you put some plywood on tope of the planks. The planks right now are able to move around independent of one another. Having a sheet of plywood above sort of allows them to do so without tearing up your tile installation. A half-inch of plywood and then the Ditra.

The fella who is specifying thin set is unaware of what's going on in the industry. Thin set won't hold the floor boards together.

01-08-2003, 10:43 PM
Welcome, Tom: :)

I'm a little concerned about your fixing " places where the floor seems to have some give, with 2x4's attached to joists and the subfloor".

A floor over 2x12s, 16 inches oc shouldn't have any give - unless these joists are spanning a very long distance. Tell us more about this "give" and the span and condition of the joists.

If you are only describing some places where the subfloor is not firmly attached to the joists, that's one thing, and some extra 2x4 nailers scabbed to the joists may help you there, but if you are flexing the joists, that's another matter entirely and your 2x4 isn't going to be of significant help.

I don't do tile advice, (John's got you covered there) but I think even Ditra wants a floor that meets L/360, and you shouldn't be feeling any give just walking on one of those.

My opinion; worth price charged.

01-09-2003, 10:15 AM
I think he's talking about blocking. He should do the easiest thing first, which would be to screw the planks down to the joists. I'm sure there's only nails there now. With T&G planks, this should be rock solid.

Water proof membrane is not really required, unless you want one. I would, if this was a second floor bath, or is regularly used by children or frisky adults. If you use Ditra, then all you need to do is use Kerdi strips to seal the Ditra joints.

Of course, I am interested in the joist spans. Just a hobby, not for profit, ya know.

tom in ohio
01-09-2003, 05:13 PM
Actually, the floor seems pretty solid in every place except where a new hole was cut for a warm air duct. The cut ends of the planks have nothing to support them. I suppose I need to use blocking in that area. :o

I screwed the planks down where the floor "creeked". That seemed to take care of the noises. The joists are in good shape.


John Bridge
01-09-2003, 07:42 PM

Yep, you'll have to block everything off so it's really solid. Tile and grout won't stand any flexing at all.