Backerboard is the generic term for the sheet material
that's installed beneath ceramic tile. Although
backerboard has been around for 25 years, it didn't
hit the mainstream until the 1980s. Before then, tile was
set on a mortar bed or on water-resistant drywall. A mortar
bed is still the Cadillac of tile backers, but mortar beds are
expensive to install, and it's hard to find someone who
knows how to do them. As a result, they're usually reserved
for high-end work. Water-resistant drywall, called green
board because of its green facing paper, costs much less and
can be hung by the drywallers. But while green board
resists water better than ordinary