ceramic tile walls
I'll let the tilers in here handle the question of whether or not it's a good idea to prime a wall before tiling it. I'd be more inclinded to tile over the skim coat of joint compound you intend to put on. Priming the wall before tiling introduces one more ambiguity into any potential problems. If the primer doesn't adhere well to the wall, and tiles start to come loose, is the problem in the skim coat, in the primer, or in the mastic or thin set, etc. If you tile over the skim coat, there's one less potential source of problems.
Yes, if it's a relatively dry area where water seldom splashes on the wall, then tiling over drywall with mastic or thin set is fine.
The reason why a cement type tile backer board is needed in a wet area like a shower is because plaster and drywall and greenboard will disintegrate if they get wet repeatedly, so a small crack that allows water into the wall turns into a bigger and bigger crack as the strength of the wall behind the tile deteriorates and the tiles gradually become loose. The weakening wall results in more cracked grout, and you have a snowball rolling downhill.
Also, you don't ever want to tile over wood because wood swells and shrinks with seasonal changes in it's moisture content caused by changes in humidity and temperature. Ceramic tiles and grout simply don't have the elasticity to accomodate dimensional changes in a wood substrate. So, if you tile over wood, there's a good chance that the grout lines will crack. The expansion and contraction of plywood is smaller than the same species of lumber, but it's never a good idea to tile over any wood.
Drywall is acceptible in a dry area simply because it's dimensionally stable, and in a dry area repeated wetting won't be an issue.
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Last edited by Nestor_Kelebay; 02-03-2009 at 11:51 PM.