Tile over concrete

I have just removed the old tile in front of my fireplace. Under the tile was some "crumbly" concrete. I removed all this, and what I am left with is a 1 1/2" depression, with a concrete slab at the bottom. Do I fill the depression with concrete and allow room at the top for hardibacker and tile? Do I bond the hardibacker to the concrete? Do I allow for expansion/contraction of the hardwood floor around the depression by leaving a air gap betweeen the "new" concrete and the hardwood floor? How does one deal with the tile to hardwood floor joint, where the tile butts up to the hardwood floor?

Thanks,
Lou

 

Hi Lou,

What you tore out is called "deck mud" or "floor mud" in tile setter parlance. It's nothing more than sand, portland cement and water. For an area that small, you can buy the stuff premixed in sacks at either Home Depot or a tile supply store. At HD they call it "sand mix" (not play sand). At a tile supply it's usually called floor mud.

You can spread thin set at the bottom of the depression to bond the new mud. Mix the mud with very little water - sort of like sand castle material. Pack it into the depression and rake off the top with a straight board or some other straightedge. You are then ready to install your new tiles.

If you can find my book at the library, it goes into detail on how to mix and place the floor mud.

John

http://www.johnbridge.com