- Q.I have been called to
inspect a shower with ceramic tile walls. The substrate
is cementitious backerboard, and as far as I can tell,
the tile was installed with thinset. There are hairline
cracks running through the tiles on all three walls,
both vertical and horizontal. There is a ceramic soap
dish in the corner, and even it is cracked. It
doesn’t appear that there has been any
movement in the floor or the walls. What could be
causing the cracking?
A.Tile expert Michael
Byrne responds: Tiles generally crack for only
two reasons: loss of bond or moving substrate. In
this case, the substrate might be moving if the
studs are spaced farther apart than 16 inches
on-center, allowing that backerboard to flex.
Another possibility is that the backerboard was
cracked prior to installation. Although
cementitious backerboard often has minor cracks
that don’t cause problems, over-stressing
the boards during delivery or installation can
cause more serious cracks. If the backerboard was
installed over a layer of drywall, then water
penetration through tile joints or corners may have
soaked and softened the drywall.
If the tiles have parted from the setting bed,
they can break when someone applies pressure on the
poorly supported tile. A tile can also crack if it
is installed over two different substrate materials
or an expansion joint. Tiles are strong only when
they are cushioned in a bed of adhesive and
surrounded by grout.
Solving the problem will require removing the
tiles so that the substrate can be inspected.