QUESTIONWe are in the process of doing a remodel and we had installed Unicomstarker porcellanato flooring, a plank style flooring. After installation we have noticed several hallow locations when we tap on the porcellanato tile. This flooring was installed on an existing concrete slab where existing ceramic tile was removed. We r being told it was installed on a mud slab. Is this hollow sound normal and can there be potential lifting of tile in the future? Can u respond w your professional opinion?
ANSWERANSWER - First of all, hollow sounding tiles is not considered a defect. There are no standards addressing hollow sounds, other to say that hollow sounds don’t necessary mean it is a problem.
Hollow sounds can be an indication of a deficiency; particularly if some tiles or parts of tiles sound hollow and other parts do not. It could be an indication that there are voids or loose tile or something else loose within the tile assembly; or hollow sounds can be an indication of the type of material or the substrate configuration to which the tile was installed over.
Based on your description, the hollow sounds could becoming from the original mortar bed on the concrete slab. If the it is an unbonded mortar bed with a cleavage membrane and wire reinforcement suspended within it then it would tend to sound hollow. You would expect it all to sound hollow then. If the mortar bed was a bonded mortar bed to the concrete slab and some of it debonded from the concrete slab, for one reason or another, that could cause some spots to sound hollow. If this is the case it is possible that the mortar bed is stable and will perform well. The only way to make sure is to remove a few tiles in various sounding conditions for verification.
ANSI A108.5 standard for installing floor tiles says that the average uniform contact area shall be not less than 80% contact except on exterior or shower applications that should have 95% contact. It says that the 80% or 95% coverage shall be sufficiently distributed to give full support to the tile with particular attention to this support under all corners of the tile.
According to TCNA 2016 Handbook and the MIA, for natural stone the minimum coverage is 95% with no voids exceeding 2 square inches (size of a golf ball) and no voids within 2 inches of the corners. All edges of the stone are to be fully supported.
Where there are excessive voids the tile is susceptible to damage if something heavy is dropped on it or something is moved over it with a heavy concentrated load.
The ANSI A108.5 standard does say “average uniform contact” and “sufficiently distributed to give full support” regarding the thin-set adhesive between the back of the tile and its substrate. On that basis, large voids under the tile is not acceptable.
Spot bonding of tile that only gives partial contact leaving large voids is not an acceptable method for tile installed on floors with thin-set mortars.