A: Usually only the Surface, but in some areas apply mortar to the Tile as well
Typically in a proper tile installation, make sure all your tiles are washed and cleaned so there is no dust or residue on the back side of your tiles. If you don't your thin set will stick to the dust and not the tile. Typically, you apply the thin set to the surface (floor or wall) that you are tiling not the tile. However, in order to achieve a really nice flat surface you may need to add thin set to back of tiles in certain areas, which is called "back buttering" to flush out to adjacent tiles on a floor that is not level.
I agree with Nicolette above, typically you only have to apply the thin set to the floor or the wall. But, in case where the wall or the floor has imperfections and cause the face of the tiles to not line up, you can butter the back side of the tile to help level them out. I hope this was helpful. God Bless!
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Holly C Bertsch Champaign Urbana, IL
A: I do this a lot...
We mortar the floor with a 1/4 " notched trowel and then place the tile upon the floor. When we are doing a wall, like in a bathroom shower, we also back butter the shower tiles. That helps them stick to the wall better.
In general when I am laying tile, I get a few down and then don't space the next tile when I am laying it. I drop it right in the corner of two other tiles and pull the right spacing out from the corner of the other two tiles. This not only keeps the mortar off the edges of the tile, but helps it stick down better. If you need any advice, go to our website and email us (contact page) and I will help you out. We give free advice! http://thi.itgo.com
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Michael Chicago, IL
You apply mortar to the floor the set the tile on top of it. Gently push the tile to attach to the mortar. Hope this helps you.