Drywall is a good underlayment for ceramic tile, if it is solid and firmly adhered, but special moisture-resistant types should be used in bathrooms, kitchens or other areas exposed to moisture. Ordinary gypsum drywall and its paper covering are susceptible to damage if any water gets in through the grout or seams in the tile. Drywall also generally needs to be sealed before any tile mastic is applied.
Opinions Differ
Ask three builders, remodelers or tilers if drywall seams need to be taped and sealed before tile is installed, and you're likely to get at least four opinions. Some experts say tile can be applied to drywall without covering seams if the drywall is secure and in good condition. Others caution that any gaps in the drywall leave openings for moisture, which can damage tile mastic and eventually cause tiles to loosen.
Many Routinely Tape
In practice virtually all builders and remodelers will routinely tape and seal seams in drywall even if the wall is destined to be tiled. And in practice, many tile installers will not put tile on unfinished drywall because of the possibility of moisture in gaps that could affect the installation and its workman guarantee. Most ceramic tile is installed in kitchens, bathrooms and other areas exposed to moisture.
Adds a Step
Taping and covering drywall seams with joint compound adds a step in the construction process, which may require an extra day while the compound dries. But taped seams to be covered with tile don't need the extra finishing and smoothing coats of those on painted or papered walls, so sealing the seams is a simpler process. The cost of tape and compound is negligible compared to the potential for moisture damage.
Backerboard
Drywall often is covered with backerboard before ceramic tile is installed. Backerboard is a thin masonry product easily affixed to drywall to provide a more moisture-resistant surface with better adhesion for tile mastic than drywall. Joints and seams don't have to be taped if backerboard is to be installed. Some tile installers will insist on ceramic backerboard in showers, bathtub walls and other areas of high moisture exposure.
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