why do tiles tent?
Reports & claims that this occurrence is
predominantly greater with local ceramic tiles, and less so with imported tiles
has not been proven conclusive. Porcelain tiles as well as natural stone tiles
have been known to "tent" as well.
Ceramic tiles experience what is termed as,
"irreversible moisture expansion". This generally occurs during two
points in a tiles life.
Firstly during the manufacturing process, after the tiles have been removed
from the kiln, they remain hot and needs to be gradually cooled down at room
temperature. This can sometimes take as long as 36hours. In the cooling
process, the tiles ‘suck-up’ moisture from the air, which results in the tiles
remaining in an expanded state and not contracting to its intended technical
spec. This expansion is irreversible and often contributed to tiles having
variations in size.
The second time, which often is the most
critical, is during the installation of the tiles. At this point the tiles
‘suck-up’ moisture from the tile adhesive, indirectly fast curing the adhesive
such that it sets in less than the manufacturer recommended time it takes for
effective adhesion to occur. At this point the tile, due to the water
absorption, also ‘grows’ irreversibly. Latex based additives such as Key It and
Bond It are normally recommended to slow down the curing process as well as add
elasticity to the adhesive.
One is likely to encounter manifested problems
associated with tiles that have a high water absorption rate especially during
periods of the year where extreme temperatures are experienced. The more water
absorbent a tile is, the higher the risk of irreversible moisture expansion.
In hot months the tiles, substrate and walls
would normally be in an expanding state. This growth of the tile, without the
latex based component that allows the adhesive elasticity, would be far too
great for the adhesive to cope. The tile grows in all lateral directions,
inevitably pushing against one another, causing stress and tension one upon the
other with no room to move, the adhesion breaks resulting in what is termed as
tenting (when tiles lift in a tent-like formation).
Likewise in colder months when the substrate
and walls are contracting, the tiles that are already in an irreversible
expanded state cannot cope with the rapidly contracting surrounds. The tile
adhesive as well, is contracting while the tile remains expanded. Adhesion
becomes stressed, inevitably reaching a breaking point giving way to the tile
breaking free (vaguely described as ‘gun shots going off’).
Contributing factors that would encourage
tenting would be:
Poor quality or
Incorrect tile adhesive being used.
Surplus tile
adhesive between tiles not being removed during installation (each tile should
be separate one from the other, not connected to each other with tile adhesive
in between).
Tile adhesive
being used as grouting.
Key It / Bond It
(Latex Additive), not being used. And if used then not being used correctly,
e.g. over-dilution
Grouting joints
being less than manufacturer recommended spec.
Expansion joint
not being used. And if used, not corresponding with substrate construction
joints &/or minimum required perameters.
Lack of perimeter
expansion joints (this could even remain open without using a proper silicon
joint, provided all cement and any other inhibitor is removed and joint remains
clean).
Thermal shock
especially during winter and summer months where there is a sudden rise or fall
in the room temperature. Commonly associated with areas where air conditioners
are used and an external door is suddenly opened, allowing rapid air-movement
out of the climate controlled area.
The above are but a list of a few contributing
factors, least to mention one has to consider the workmanship behind the
installation, the type of product you're using, the surface you're tiling on,
and so on. If all considerations had been taken into account, including the
inherent irreversible moisture expansion of the tile mentioned, then there
should be no reason why the tiles would lift.