New floor 3 1/2" above existing slab [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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05-16-2006, 07:14 AM
I'm extending an interior room into space stolen from the garage. It'll be an area about 6'x9' when finished. The garage and house slabs were poured as one, but the garage is about 3 1/2" lower than the house. Finished floor will be 16" ceramic tile laid diagonally, matched up with the floor in the house. The question is how to match up the new floor with the floor in the house.

The obvious answer is to pour a new slab on top of the garage floor. I don't like this for several reasons, so I'm thinking of doing the following; any comments?

1) lay 30# felt on the existing garage floor
2) set 2x "joists" on the felt, spaced 12" o.c., ripped to provide a level plane, even with the upper slab, bolted down and into the upper slab
3) use either 3/4" exterior plywood or 2 layers of 5/8 glued & screwed on top
4) use Ditra to decouple all this from the tile layer


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05-16-2006, 07:58 AM
Mike, you will need an expansion joint where the new floor abutts the concrete. Of course, you'd need one there even if you used concrete or mud to level the floors.