The topic of spot bonding floor tile was covered in CTEF Tile Tip about a year ago, and one would think the installers that utilize this technique would heed the warning and stop installing tile in this way. Unfortunately, that has not happened.
This problem continues to be high on the list of questions received by the CTEF offices when things go wrong. Too many installers continue to spot bond their floor tile by placing a dollop of mortar (about the size of a golf ball) on each corner with one in the middle of the back of the tile. This process, commonly known as “five spotting,” fails almost every time because the majority of the tile is not supported or bonded by the mortar (see attached photo).
The TCNA Handbook method W260 illustrates the installation method for spot bonding ceramic tile on walls only, using a particular epoxy setting material which is recommended by the manufacturer for this specialized purpose. This detail is very specific and clearly is recommended for interior use on a wood or steel stud wall over cement backer board. It further states these limitations: It will not withstand impact and the maximum stud spacing is 16" on center.
The number-one problem caused here is the lack of support of the tile...Another problem occurs when moisture collects in these hollow areas, causing the grout to remain dark until the water has completely evaporated. If the tile is a natural stone, the moisture could permanently discolor the stone [and] the grout.
The reason installers use this “shortcut” to install floor tile, especially large format, is that it virtually eliminates lippage. With the mortar concentrated in these five areas, the installer can easily push down on the mortar spot and get it to flatten out with the adjacent tiles. Continuing to push down on the other three corners usually yields a lippage-free installation. Life is good, right? Wrong!
This mistake creates a number of problems which many times will be cause for a callback and/or potential failure. The number-one problem caused here is the lack of support of the tile. Any point load, including a woman’s high heel, will cause the tile to crack. The second problem occurs when a hollow sound is detected in the area which has no mortar underneath—which is not acceptable. Another problem occurs when moisture collects in these hollow areas, causing the grout to remain dark until the water has completely evaporated. If the tile is a natural stone, the moisture could permanently discolor the stone, not to mention the grout.
In order to save yourself a lot of time, trouble and possibly financial loss, use the industry recommended method to spread your mortar. Properly key in your mortar to the substrate, comb it in one direction and place the tile into the mortar moving it in a back and forth motion perpendicular to the trowel ridges. This method should provide the necessary mortar coverage while keeping problems away from your door and keeping the money you have earned in your pocket—where it belongs!