QUESTIONWe had 8”x48” large format porcelain tile installed floor to ceiling on 2 walls in our home for a total of 270SF. Our ceilings are 9ft. The tile was installed directly onto painted (not newly painted) drywall. Work being done on our home now a year later caused a tile to have to be removed. It turns out these tiles were spot set (bonded). Each tile weighs over 12 lbs & each tile appears to have 3-4 blops of white adhesive holding it on the wall. The adhesive is sort of dry & caulk-like in its dry state. I have been told spot setting was prohibited except in 4 fairly specialized installations. Is this correct? Does the TCNA handbook specifically say it’s prohibited or do they just not list it as the accepted manor in which to install tiles such as these? Is this a failure waiting to happen? What steps do I take from here to have this corrected? Thank you for any help you can give me with this.
ANSWERANSWER - Adhering a tile using a spot bonded method , where the installer typically applies a spot of cementitious thin-set adhesive in the four corners of the tile and at the center of the tile, or less, is not an acceptable installation method unless they are using an epoxy adhesive on an interior application.
Spot boding in effect reduces the amount of surface area that is bonded; thus the potential bond strength is reduced by that percentage. So if only 50% of the tile is bonded then the potential bond strength is reduced by 50%. The industry standards state that tiles should be bonded so that at least 80% of the tile is bonded for interior dry applications. For interior wet applications or exterior applications 95% contact is required. In both cases the contact has to provide uniform contact and full support at tile edges and corners.
The TCNA Handbook does say spot bonding with cementitious adhesives is not acceptable, but they do show a spot bonded wall method using an epoxy adhesive, which has about 5 times more bond strength than a cementitious thin-set adhesive. There are not floor spot bonded methods allowed.
Spot bonded methods reduce the potential bond strength, it leaves voids that if subjected to heavy loads or impacts can crack or crush, and excessive voids allow moisture to collect behind the tile that can lead to various issues.
Because the cementitious thin-sets provide a lot of bond strength, even if the tile is 50% bonded (if properly bonded) it is still substantially attached. So it doesn't mean the tile will fail if it is spot bonded.