- Q.Should an underlayment be
used with ceramic tile over a plywood subfloor? If so,
what material would you recommend?
A.When bonding ceramic
tiles with an adhesive, you should use an
underlayment to absorb movement in the
subfloor.
Otherwise, the movements, caused by the
expansion and contraction of the wood subfloor with
changes in moisture content, can crack the
inflexible grout between the tiles. A reinforced
cement-board, such as Wonderboard or Durock, works
well as an underlayment. It is nailed to the
subfloor and the tile is attached with adhesive
over it. The old method of notching the floor
joists to drop the subfloor and setting the tile in
a thick mortar bed on the subfloor works well, but
is seldom used today.