What is Tile Hollowness?
A hollow sound which is heard when tapped with a mallet shows that the tile or a portion of the tile is not bonded or that there is a void under that portion. The hollow sound could also be a characteristic of that particular tile assembly. Un-bonded mortar beds have a different sound than bonded mortar beds. Tile installed over wood sub floors have a different sound than tile installed over a concrete base that gives more of a solid sound. Tiles bonded to membranes have a different sound. Voids in the substrate or substrates that are not bonded, will also give a hollow sound.
Causes:
- Uneven sub floor will not have uniform bonding with adhesive or mortar with tiles and the sub floor
- Improper cleaning of the floor before tile installation
- The concrete substrate is not properly prepared. Concrete curing compounds may act as bond breakers or the concrete surface is too dense and doesn’t absorb moisture well enough to allow thin-set to achieve an adequate bond
- The under-sides of the ceramic or stone tiles are not properly cleaned before application. Dirt and manufacturing residues are contaminants and act as bond breakers
- Improper slaking or mixing of mortar or adhesive
- Some installers install the tile using a spot bond method where they only put dabs of thin-set, which isn’t an acceptable industry standard method
- Lack of supervision
- Poor Quality of a materials used like screed, mortar, adhesive and tile etc.,
- The thin-set adhesive could have de-bonded from the back of the tiles, or the thin-set could have de-bonded from the substrate
- If the substrate is a bonded mortar bed, it’s possible that the mortar bed has de-bonded from the concrete slab
- Other factors that contribute to de-bonding are excessive floor or wall deflection (vertical movement) and the lack of movement joints (expansion joints)
- Membranes will normally cause a hollow sound
- It is possible that if you walked on a tile installation before it was well cured, it could compromise the tile’s adhesion
- Large or oversized tiles require a certain troweling technique to ensure that they achieve a strong bond with the adhesive. All tiles need a gentle whacks with a wooden object when being installed to set them in the adhesive
- Use the proper bonding material. If a dry powder bonding agent is used, you should check whether it is properly mixed or not otherwise it may result in pop up of tiles
- Using old tiles may also cause the tile floor buckling. Old tiles may get brittle. With passage of time, they lose flexibility and are not able to withstand changes due to temperature variation
- The high amount of concrete shrinkage
Effects:
- The lack of support beneath the tiles may causes cracks or damages
- Replacing damaged tiles may cause shade/color variation
- Re-work may affect office/personal time
- Need to spend more money for rework compared to new work
- Lack of skill in rework can lead to additional cost
- Extra tiles needed for the future should be kept in stock just in case they do get damaged
A simple way to check for the hollowness in tile of granite or marble is;
- to tap on the tiles with a hard and flat object such as a wooden mallet
- Chains or special sounding devices can be used for larger areas
If the tile is well bonded (attached to the concrete substrate), it will have a low-pitched sound.
If you hear a higher pitched or a hollow sound, this indicate that tiles have de-bonded or were never bonded, somewhere within the tile assembly.
The reason for checking for hollow spots in tiles is due to the possibility that if left unchecked, this can lead to tile cracking and aside from aesthetics, it could also pose a tripping hazard.