Some thinsets list it, with conditions. Custom Building Products’ VersaBond and FlexBond list exterior grade plywood in interior residential and light commercial dry areas, and LATICRETE’s 253 Gold, 254 Platinum and MULTIMAX Lite list exterior glue plywood, interior only. LATICRETE’s 253 Gold and 254 Platinum sheets spell out two layers of plywood under the tile, and Custom’s and LATICRETE’s documents say not to bond tile directly to OSB, luan, particle board or hardwood.
What each data sheet says about plywood
| Product | Plywood on its sheet | Not to bond to directly |
|---|---|---|
| VersaBond (Custom Building Products) | Exterior grade plywood, interior residential and light commercial dry areas | Hardwood, luan plywood, particle board, OSB panels, metal and more |
| FlexBond (Custom Building Products) | Exterior grade plywood, interior residential and light commercial dry areas | Hardwood, luan plywood, particle board, OSB panels and more |
| CustomBlend (Custom Building Products) | Exterior grade plywood (interior residential and light commercial dry areas), listed for the powder mixed with Custom’s Thin-Set Mortar Admix | Hardwood, luan plywood, particle board, OSB panels, metal and more |
| MultiSet (Custom Building Products) | Not directly on exterior glued plywood; Custom says to consult its Technical Services | Hardwood, luan plywood, particle board, OSB panels, metal and more |
| 253 Gold (LATICRETE) | Exterior glue plywood, interior only | Particle board, luan, Masonite or hardwood floors |
| 254 Platinum (LATICRETE) | Exterior glue plywood, interior only | Particle board, luan, Masonite or hardwood floors |
| MULTIMAX Lite (LATICRETE) | Exterior glue plywood, interior only | Particle board, luan, Masonite or hardwood floors |
| Ultraflex 2 (MAPEI) | Group 1 exterior-grade plywood, CC-plugged or better, for interior residential and light commercial floors and countertops in dry conditions only; its sheet says it meets ANSI A118.11 when mixed with water | Hardwood flooring, OSB, substrates containing asbestos, or metal |
From each product’s technical data sheet. Custom’s lists also name parquet, cushion or sponge-back vinyl flooring, fiberglass and plastic; FlexBond’s list doesn’t name metal.
The floor under the tile
LATICRETE’s note on wood floors (TDS 152) says single-layer subfloors aren’t acceptable for bonding tile directly without a properly installed underlayment, and that every subfloor panel must be APA Exterior or Exposure 1 rated. Its 253 Gold and 254 Platinum sheets spell out the floor:
- Subfloor: 5/8 inch exterior glue plywood, tongue and groove or with every edge blocked, over bridged joists no more than 16 inches on center.
- Underlayment: a second layer of 5/8 inch exterior glue plywood, glued to the subfloor with construction adhesive, fastened every 6 inches along the sheet ends and every 8 inches across the field, with its joints offset from the subfloor’s.
- No interior plywood: TDS 152 says interior plywood isn’t acceptable as underlayment. It accepts Exterior-rated grades and Structural I panels, and it accepts mortar beds and cement backer units in place of the plywood underlayment.
- Stiffness: Custom’s VersaBond and FlexBond sheets ask for a maximum allowable deflection of L/360 under tile and L/720 under stone. LATICRETE’s 253 Gold and 254 Platinum sheets and its TDS 210 ask for L/360 under tile and L/480 under stone.
Custom’s FAQ gives two answers
Asked whether tile can go directly over a plywood subfloor, Custom’s FAQ says yes, provided the floor has a tongue and groove subfloor with an additional layer of APA exterior grade plywood on top and is built to tile industry standards; it gives 1 1/4 inch as the nominal thickness. It adds that plywood isn’t a stable surface, and that a polymer-modified mortar meeting ANSI A118.11 is required. In its answer on cracked grout, the same FAQ says not to set tile directly over a flexible surface like plywood. Both answers point to the same fix: its WonderBoard Lite cement backer board, set in latex-modified mortar and screwed over the plywood, which Custom calls a superior alternative to bonding to plywood.
On the product side, Custom’s CustomBlend sheet lists exterior grade plywood among the substrates for the powder mixed with its Thin-Set Mortar Admix, not among those for the powder mixed with water, and its MultiSet sheet says not to bond directly to exterior glued plywood. LATICRETE’s plywood troubleshooting sheet (TDS 210) lists an improper thinset as one cause of cracked tiles or grout and points to 254 Platinum, 254 Platinum Plus or MULTIMAX Lite.
Mastic on plywood
- AcrylPro (Custom): exterior grade plywood in interior residential and light commercial dry areas; not directly on hardwood, luan plywood, particle board or OSB.
- 15 Premium Mastic (LATICRETE): the sheet calls it ideal over plywood, but its substrate list says exterior glue plywood for floors only, and its limits rule out interior glue plywood, OSB and luan.
- Weldwood Multi-Purpose Ceramic Tile Adhesive (DAP): underlayment grade plywood, interior use only. On floors, DAP says exterior grade plywood must be securely fastened and free of flexibility, and its chart recommends no product over particle board or lauan chipboard.
Wet rooms and outdoors
TDS 152 says plywood isn’t a suitable surface for tile where it’s exposed to excessive moisture or humidity: steam rooms, showers, pools, fountains, over damp basements, or outdoors. Custom’s FAQ says plywood, drywall and even water-resistant drywall can be damaged and will deteriorate under continuous moisture. We’d keep tile on plywood out of wet areas altogether.
VersaBond’s sheet says it contains Portland cement and free silica: avoid eye contact or prolonged skin contact, don’t breathe the dust, and wear a NIOSH approved respirator. LATICRETE’s 253 Gold sheet says its powder causes severe skin burns and eye damage, and to wear protective gloves, clothing and eye protection.
Gluing a small piece of tile to wood instead?
Tile to wood