My tile is bonded to a concrete slab. Why do I have cracks?
While it is impossible to speculate on the exact cause of cracks without an inspection, some reasons for cracking include but are not limited to:
Whenever tile is bonded to concrete, movement in the concrete will cause cracks to occur in the tile layer.
Should cracks occur in the concrete, these cracks will "reflect" through the tile - this is often called "reflective cracking." Similarly, if tile is installed over a control joint (The Tile Council of North America does not recommend this), movement in the control joint will cause a crack in the tile. Even small shrinkage cracks in concrete can be dimensionally active where continued curing of the slab will cause these cracks to expand or propagat. If this occurs, the cracks will show through the tile.
This type of cracking can be easily avoided - either by installing the tile on a mortar bed set over a cleavage membrane (for example, TCNA Handbook detail), or by installing the tile over a crack isolation membrane using a thinset method.
What is the difference in a mortar bed and cleavage membrane installation and a thinset installation using an anti-fracture membrane?
In the mortar bed installation, the mortar bed is not bonded to the concrete - rather it is isolated from cracks in the concrete by the cleavage membrane. This allows the tile to "float" over the concrete.
In the thinset installation, a crack isolation/anti-fracture membrane is bonded to the concrete. Tile is bonded (with thinset) to the surface of the membrane. The internal make-up of this membrane is such that movement in the concrete is not directly transferred to the tile. The membrane compensates where needed to prevent or reduce force transference.
These membranes are either trowel applied or sheet applied. In many cases, multiple components or steps are part of the system. Performance also varies. It is important to check with the crack isolation manufacturer regarding their installation instructions and intended use.
If I use a crack isolation/anti-fracture membrane, can I eliminate the expansion joints in the tile work?
It is a frequent misconception that anti-fracture membranes allow you to eliminate expansion joints - they do not. There always must be soft joints in the tile work to allow for expansion and contraction. The frequency of expansion joints is recommended in the TCNA Handbook.
Are there any other reasons I might have cracked/loose/hollow tile?
There are many factors that can cause tile to lose its bond to the subfloor. Losing bond to the subfloor has the potential to lead to cracking in the tile layer:
Only an on-site inspection can truly evaluate the potential reasons for cracked tile. Please visit the TCA Team for information on these types of services.
If the floor sounds hollow, does it mean my tile will crack?
Occasionally, a floor will sound hollow even when the tile is well bonded. This can occur when a mortar bed method is used and the mortar has delaminated from the supporting layer or when the subfloor itself is not sufficiently thick or well attached. Other systems that intentionally separate the tile layer from the substrate (such as the mortar bed with a cleavage membrane system like TCNA Handbook detail F111) should be closely examined to ascertain if hollow sounds necessarily imply that the tile is not bonded.
While a tile floor with hollow spots is not ideal, it does not necessarily mean that floor failure is imminent. On the contrary, over concrete, if there is no deflection in the floor; grout and gravity will help keep the floor in place (as long as there are sufficient movement joints in the tile and minimal shear forces). Over wood, floor failure is more likely. Movement in the subfloor could cause grout to break away from the tile, compounding the instability of the flooring.
Can I inject epoxy under the tile to fix the hollow sound?
Some contractors have tried to inject epoxy to rebond tile without reinstalling it. While this may work in a small area, it is not practical over a large area. Further, any repair that does not address the cause of the failure may not last very long.
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