What Are the Causes of Old Tile Feeling Hollow?

When the Hollow Sound Indicates Problems

• A hollow sound does not necessarily mean the tiles are not well bonded. Use a rubber mallet to gently tap around the room, noting areas where the hollow sound is present. Specialist applications that require a membrane be installed beneath the tiles -- but above the substrate -- can result in the same sensation. If the hollow sound is uniform across the floor, from wall to wall and tight into the corners, the hollow sound is probably not an indicator of failure.

  If most of the floor does not sound hollow, but certain areas do, this is indicative of a problem. Even this symptom does not necessarily mean the floor is about to fail; tiles laid over concrete can give years of service so long as shear forces are minimal and sound grout is in place. Laid over a wooden floor, however, the movement inherent in the substrate will probably exacerbate the problem and cause failure. Failure typically presents as spalling grout or cracking tiles; both allow moisture to pass through the tile layer and into the substrate, so the issue must be addressed promptly.

Premature Foot Traffic

• The hollow sound can occur because the tiles were walked on before the adhesive -- properly called “thinset” -- was fully hardened. Particularly dense tiles, such as those made from porcelain, require extra setting time for the adhesive. If adequate setting time was not allowed, premature foot traffic could have dislodged the tiles before they were properly bonded to the substrate.

Sub-Floor Contaminants

• Adhesive can bond well to the underside of the tile but not to the surface of a treated substrate. This can happen, for instance, when tiles are laid over a waxed wooden floor that was not adequately treated prior to laying the tile. In new-build properties, a similar situation is not uncommon when tiles are laid on plywood that has a surface waterproofing treatment.

Premature Setting

• Another common cause is that the adhesive was beginning to set before the tiles were put in place. This can occur because an extremely porous substrate wicked the moisture out of the adhesive more quickly than the installer expected, or because the installer spread more adhesive than his skills allowed him to tile over in the time available.

Insufficient Expansion Joints

• A further potential cause is insufficient movement joints and expansion joints. This is seldom an issue in domestic scenarios, but in commercial applications such transitions should be used every 20 or 25 feet. If the transitions are not present, changes in humidity and temperature can cause expansion and contraction in the subfloor that the tile installation cannot mimic, and large areas of tile simply lift like a blister. They will then sound hollow regardless of eventual settling or the return of the substrate to its original dimensions.

Rectification

• A hollow sound that transpires to be a symptom of debonded tiles does not necessarily indicate that the tiles need to be lifted and the tiles reset. Rehabilitation products are available that work well with most types of manufactured and natural tile. The process involves drilling small holes through the grout around the affected tiles, injecting a bonding agent through the penetrations until tapping with a rubber mallet no longer makes a hollow sound, then weighting the treated tiles. The curing of such products typically takes less than 10 hours.