Thinset on drywall and painted drywall

Most of the thinset sheets we read list gypsum wallboard. Custom Building Products’ VersaBond limits it to interior dry areas, and LATICRETE’s 254 Platinum to interior use only, non-wet areas. Painted drywall is harder: LATICRETE’s TDS 131 says it’s best to sand, scarify or remove the paint, and Custom’s VersaBond sheet says glossy or painted surfaces must be sanded or abraded first.

What each sheet says about drywall

SimpleSet’s sheet says both

Custom’s SimpleSet pre-mixed thinset lists plaster and gypsum wallboard (dry areas) among its suitable substrates. The limitations on the same sheet say not to bond tile directly to lightweight concrete or gypsum surfaces, and to contact Custom’s Technical Services. We’d call Custom before putting SimpleSet on drywall, or pick a product whose sheet lists drywall without that clash.

Drywall near water

254 Platinum’s sheet limits drywall to interior use only and non-wet areas, and Custom’s VersaBond and MultiSet sheets say interior dry areas. Custom’s FAQ says drywall and even water-resistant drywall can be damaged and deteriorate when exposed to continuous moisture, while cement backer boards can be used in wet areas. We don’t cover shower waterproofing here; follow the membrane maker’s instructions and your local code.

Painted drywall

LATICRETE’s note on painted surfaces (TDS 131) says a layer of paint between the tile adhesive and the wall can eventually break down or deteriorate. Moisture in the wall, or free alkali in plaster, can turn the paint into a gummy mass that makes the tile lose its bond.

• Oil-based paint: LATICRETE says all of it must come off before tile goes on.
• Latex paint: LATICRETE says some latex house paints may be compatible with some tile adhesives in interior dry areas, if the paint is sound, well bonded and not in a wet area, and that you should always run a bond test. It still calls sanding, scarifying or removing the paint the best route.
• LATICRETE’s preferred fixes: take the paint off by sanding or scarifying, or put up tile backer board, then set the tile with thinset.
• Warranty: LATICRETE says it doesn’t warranty the bond of its products applied where paint, primer or their residue remains.
• Custom’s sheets: VersaBond’s says glossy or painted surfaces must be sanded or abraded and stripped of contaminants. SimpleSet’s says they must be sanded, stripped and cleaned of waxes and dirt.
• LATICRETE’s thinset sheets: 253 Gold, 254 Platinum and MULTIMAX Lite ask for surfaces free of paint.

EPA says that if your home was built before 1978, it is more likely to have lead-based paint. If you sand or scrape old paint yourself, EPA says to use its lead-safe work practices, and not to attempt to remove lead-based paint yourself. See epa.gov/lead.

Custom’s VersaBond sheet says the mortar contains Portland cement and free silica, and to wear a NIOSH approved respirator rather than breathe the dust.