prepared to support a tile installa- tion as the surface finish. • Additional considerations for a ver- tical tile installation on gypsum board include: • Weight of the installation • Deflection ratings • Flatness of the substrate ° For Organic Adhesive: Refer to ANSI A108.4. Substrate flat- ness tolerances are listed in ANSI A108.01 2.5.2.1 and ANSI A108.02 4.1.4.2.2. Additional flat- ness tolerances are listed in the TCNA Handbook Method W242- 18 Preparation by Other Trades section. ° For Cementitious Bond Coat: Refer to ANSI A108.5. Substrate flatness tolerances must not exceed those required for ver- tical surfaces as defined ANSI A108.02 4.1.4.3.2 and as listed in the TCNA Handbook Method W243-18 Preparation by Other Trades section. ° See also TCNA Handbook Substrate Requirements on pages 30 - 33 • Environmental Exposure ° Methods W242 and W243 are rated as Res1 (Residential Dry) and Com1 (Commercial Dry). See TCNA Handbook pages 44 - 47. ° See also TCNA Handbook Backer Board Selection Guide Direct Bond to Wood or Gypsum Wall Board - Caution on page 20. • Bonding the tile to the substrate ° For any installation, the correct setting material or adhesive must be selected to bond the tile to the substrate. ° In a gypsum board installation, the setting material or adhesive must bond to the paper face and joint compound. ° If the gypsum board has been painted, the paint is bonding to the paper and joint compound and the setting material must bond to the paint. Finally, to get to your question, the NTCA Reference Manual contains a list of Questionable / Unsuitable Substrates (see page 30 in the 2018/2019 edition). Paint is listed as a Questionable Substrate. The NTCA Reference Manual advises: “Questionable substrates are substrate types that when properly designed and prepared can receive direct bond applications of ceramic tile and stone. Some questionable substrates conform to specific ceram- ic tile and stone industry installa- tion methodology when applicable requirements are followed. In addi- tion, the use of specific installation materials designed for unique appli- cant can result in a successful instal- lation. Consult ceramic tile and stone installation manufacturers for their recommendations.” What this means for your installa- tion is, once it has been determined the gypsum board and its support- ing structure have been properly designed, constructed and installed to support a tile installation, consult your setting-material manufacturer to ASK THE EXPERTS –––––––––––––––––––––––––––––––––––––––––––––––––––– 28 TileLetter | January 2019