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.
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