Hollowness explained
While you walk on a flooring and at a particular spot your shoe makes a different sound, you get alerted that something is not alright with the flooring below. This is a typical case how hollowness in flooring is felt by anybody. The professionals check for hollowness in flooring by special tools like wooden mallet, plastic tipped Mallet, metal ball tipped tool etc.,. The change in sound when tapped with the tool indicates presence of hollow space or lack of adhesion of the flooring tile to the base below.
Effects of hollowness
Hollowness beyond a limit causes the floor tile to crack while any load comes on it. This could be a person walking or leg of a furniture like table or cot resting on the hollow zone of tile. In extreme case it is seen that whole tile rocks freely and can be lifted off from the floor by prising at the joint by a sharp screw driver. Depending on severity tile needs to be replaced to avoid the look of a damaged floor.
Acceptable limits of hollowness
Indian standard codes are silent on any tolerance for acceptable limits, advocating zero hollowness. This is difficult to achieve in practice and very expensive if aimed at. Australian standards allow 20% tolerance in hollowness for an individual tile. This is not 20% of area of a room but 20% of area of an individual tile. This appears an acceptable trade off.
Causes of hollowness
- The primary cause is not following the proper procedures while laying the tile
- Insufficient supervision during the flooring work.
- Mixing too much of water in mortar mix used below the tiles, leading to evaporation and leaving voids on drying up.
- In large rooms/areas laying the tiles wall to wall without leaving gap for thermal expansion and contraction in the ends, leading to popping up of tiles when the space contracts.
- Using a mortar bed of thickness in excess of 50 mm for laying tiles which may eventually shrink on setting of cement, leaving the tiles de-bonded.
- Use of untested, nonstandard resin bonded base materials for laying also is seen yielding disastrous results.
Rectification / remedies
Spots of hollowness can be rectified by injecting or grouting of resinous material under pressure by making a small incision on the nearest point at the joint. In case of marble, a small hole can be drilled at the middle of hollow spot and is filled back after grouting. This job can only be done by professionals and is a better option to replacing the tile but may not always yield 100% result.
The last option is to remove and replace the tile properly. This comes with share of its own disadvantages. While removing a particular tile, adjacent tiles may also get damaged and the finishing will not always match with the original work. Major issue will be that invariably the newly laid tile will not be of the same shade as it comes from a different batch of manufacture.
Learning
Replacing option should be avoided if you can live with it especially if the hollow tile is in the edge or an insignificant corner of the room without much load coming on it.