determine which of their adhesives or mortars (and possibly primers) are recommended to bond the tile to the painted gypsum substrate. Obtain from them a job-specific written war- ranty covering the installation. If you find the walls have not been properly designed, constructed and installed to support a tile installa- tion, speak with the owner, general contractor and other trades to discuss what needs to be done to bring them into tolerance. Generally speaking, when you install the tile, you are accepting the substrate. If you need to re-fasten, prepare or render the substrate for flatness, make sure you have an approved change order to get paid for the work. The NTCA Reference Manual goes on to say “Certain questionable sub- strate types can receive ceramic tile and soon installations when installed with a…. cleavage membrane/lath and plaster wall assembly.” This means another option would be to follow TCNA Handbook Methods W221 and W222 which can use the installed gypsum board as a solid base for a mortar bed installation. Please watch this episode of Question Mark on NTCA’s TileTV that shows a commercial wall substrate that did not meet stan- dards for a tile installation: http:// www.iwantmytiletv.com/index. php?video=1B7E5CA9 or https://bit. ly/2T3f5AV I hope this helps. – Mark Heinlein, NTCA Training Director ASK THE EXPERTS –––––––––––––––––––––––––––––––––––––––––––––––––––– High Quality Metal Trims and Pre-Molded Expansion Joints for all of Your Flooring Needs Call or click today! 800.236.5230 www.ceramictool.com Carpet/Vinyl Trim Reducers Reverse Trim Ceramic Tool MADE IN USA 30 TileLetter | January 2019