why must you use cement board under ceramic tile?
Hey almost right! Backerboard is for strength and adhesion Contrary to popular belief, it's not waterproof, so don't expect it to be. Tile needs a firm base so it won't crack or come detached. You do still need a solid floor under it. Over concrete, it's not needed. You can also use a product called Ditra which is a plastic that can go over most surfaces. Stay away from Hardibacker. It's too rigid and has a tendency to leave voids between it and the subfloor.
You use hardibacker because it will not expand and shrink like plywood and thus your tile will not crack. It will not retain the moisture that wood does and the mortar bed for the tile will adhere better. It also gives support to the tile and floor in that it will not flex when you walk over it as opposed to plywood. However, even with the use of hardibacker you still have to have a good sub floor under it...usually 3/4 plywood. The hardiback comes in different thicknesses as well and depending on your sub floor this will determine the thickness of hardibacker. Unless you have a concrete floor and then you can apply the tile directly to it...if it is level Go to Lowes and talk with the flooring people....they can walk you through it and there are pamphlets that show you what to do. good luck
It is not necessary to use cement board under ceramic tile unless the area is gong to be exposed to water or moisture frequently. The cement board creates a water barrier to protect the wood framing of the house. Ceramic tile can be successfully laid over wood, plastic, fiberglass or any other surface that is flat and solid. That means no give or flexing when you walk on it or sitting things on it. A wooden floor normally will require extra bracing to make it solid and not flex from walking on it or furniture weight.
