Ceramic Floor Tile
Buckling
By: Tim Morgen, P.E., Principal
CENSpace Structural Engineering
I was recently retained by an
insurance company to inspect a rather unique and strange
occurrence in a residential home in New Mexico. It seems that
the homeowner’s ceramic floor tile had buckled upward in the
center of the family room, virtually overnight. Though the
tiles and grout did not crack, they popped up forming a ridge
that was evident one morning when one of the owners let the
dog outside.
To provide some brief
background information, this is a single story home built in
the mid 1970s. About ten years ago, the homeowner’s decided to
have this 12’x15’ family room addition built off of the back
of the home. The new foundation was constructed using a
monolithic slab with the perimeter strip footing that extended
down about 36” to the frost line. The new addition was covered
with stucco to nearly match the existing façade of the home,
then about three years ago, a stucco contractor finished the
entire home with a new coat of stucco to make sure everything
matched.
One unusual condition that I
found upon my inspection was that this new stucco façade
extended down into the soil along the exterior of the home in
several locations, particularly at the back exterior wall of
the family room addition. The homeowners stated that the
stucco contractor told them that the new type of stucco that
he was using was adequate to withstand soil exposure. A quick
tour of the neighborhood verified that most homes with stucco
siding did run the material down into the surrounding grade
though building code requirements require several inches of
space between the bottom of the stucco façade (or other façade
materials) and the exposed soil grade.
I pulled up some of the
buckled tiles and measured a gap between the underside of the
tile and the concrete slab of about 1-3/4”. I also measured
the concrete slab using a digital level and found the slab to
be perfectly flat. Then I tapped each 12” x 12” ceramic tile
of the new floor with the grip end of a screwdriver and
discovered that many of the tiles had a hollow echoing sound
to them once tapped. The pattern of looses tile extended from
the buckled center portion of the floor and fanned out toward
the back exterior wall of the family room addition. The bottom
12 inches of this exterior wall was measured to have a higher
moister content than the upper portions of this wall (using a
non-destructive moisture meter along the outside stucco
surface). It had not rained or snowed for several weeks prior
to my inspection.
My subsequent research of this
phenomenon revealed that some types of ceramic tiles are more
prone to moisture expansion than others. Unlike small
dimensional changes due to thermal expansion, moisture
expansion of tile sometimes does not go back to its original
size when dried. There does not appear to be an industry
standard for the level of moisture expansion for different
types of tiles, though the Ceramic Tile Institute of America
recommends that there be a limit on the allowable moisture
expansion (expressed as moisture coefficient percentage) of
tile. Expansion of tiles from moisture can result in high
shearing stress between the tiles and the concrete slab
resulting in tiles suddenly lifting or buckling upward as was
observed in this home. Other instances of sudden tile buckling
such as that described in this case have been documented in
other homes, and in one case, the homeowner acknowledged
hearing the floor tile crack and actually saw tile buckle
upward in the kitchen.
Much of the discussion that I
have read on this subject as well as from people who have
experienced this phenomenon in their own homes suggest that
the tile buckling was due to soil heaving or other foundation
movement. However, it is clear to me in this case, that
moisture wicked through the exterior materials of the home
through an improperly installed wall membrane. Slowly water
seeped through the floor under the ceramic tiles and caused a
sudden popping of the tiles due to stresses built up from
moisture expansion. The ridging occurred in the center of the
floor because this was the path of least resistance to relieve
the stresses induced into the floor membrane.
