QUESTIONI recently had my bathroom remodeled. The contractor used the spot setting method on the tub/shower surround. I asked him about the honeycomb of voids this was leaving behind the tiles and what about water getting behind them. He said the grout would take care of that. I'm worried that over time I'm going to have problems with water build up or the tiles coming off the walls. Through researching the internet I found this type of tile setting should be banned. Is my concern a valid one or am I worrying for nothing? Is spot setting tile an approved method?
ANSWERANSWER - Spot bonding tile is not a legitimate method for installing ceramic tile, including porcelain tile, which is a type of ceramic tile, or stone tile, unless an epoxy adhesive is used in an interior vertical dry application.
Spot bonding is typically where the installer applies spots of adhesive at various spots on the back of the tile that leaves substantial voids behind the tile. This results in adhesive contact that is substantially less than the requirements of having at lease 80% evenly distributed contact with full support at edges and corners for residential applications. Or for interior wet areas or exterior applications or for commercial floor applications you should have at least 95% adhesive contact that doesn't have any voids greater than 2 square inches (size of a golf ball) with full support at edges and corners.
Normally a honeycomb appearance of the adhesive is due to the installer applying the adhesive to the back of the tile in one direction and then applying the adhesive to the substrate in the opposite direction, and then not properly embedding the tile to prevent voids. This condition can also result in excessive voids in the back of the tile.
One problem with spot bonding on floors is that wherever there are voids under the tile it makes the tile vulnerable to cracking or crushing at those spots if they are subjected to a live point load. The unsupported corners and edges of floor tiles are particularly more vulnerable to damage. It also can cause the tile floor to have hollow sounds wherever the voids are located.
Another problem with spot bonding is the fact that whatever percentage of voids you have under the tile, you have diminished the potential bond strength of that tile by the same percentage. So the tile will be less resistant to various stresses.
A problem with spot bonding in exterior or interior wet areas is that water can collect behind the tile in the voids, so the voids become a reservoir of moisture that then excessively subjects the tile to moisture. This can lead to efflorescence staining, microbial growth, freeze thaw damage in those geographical climatic areas, and spalling in natural stone.
A porous cementitious grout will not prevent water from migrating through the grout to the back of the tile.
Tile Council of North American (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation has TCNA Method W215-16 Ceramic Tile and W260-16 Stone for Spot-Bonding Stone with Epoxy adhesive for wall applications. These standards only recommend this method for interior dry applications. This is where only about 10% of the back of the tile is bonded with an epoxy that will potentially achieve a bond strength attachment that is about 4 times greater than a typical modified thin-set mortar.