How to Prime Plywood for Thinset Mortar

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Things You'll Need

  • Broom or vacuum

  • Rag

  • Mineral spirits

  • Level

  • Sandpaper

  • Putty knife

  • Filler putty

  • Tack cloth

  • Hammer, nail set, drill or screwdriver

Plywood floor must be properly primed and prepared for thinset.

Thinset mortar is the primary method for installing ceramic or stone tiles onto new surfaces, acting like cement to bond the tiles into their new homes. Most tiles are approved for installation over solid plywood floors, but before you can spread the thinset and lay the tiles, you have to prepare the plywood to make sure it is compatible with the adhesive. Improper priming and preparation will lead to cracks, bumps or slopes in the tile floor that can eventually cause serious dangers to those walking.


Step 1

Sweep or vacuum the floor to remove all dirt and dust. Wipe down the floor with a rag dampened in mineral spirits to work off any oil, grease or wax. Do not saturate the floor.

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Step 2

Run a level across the surface and circle any high points or low points with chalk. Sand down high points with rough-grade sandpaper until those areas are flush with the rest of the floor. For low areas, use a putty knife to spread filler putty over the area to bring it flush. Allow all repair work to dry before continuing.

Step 3

Sweep, vacuum or rub down the floor with a tack cloth to remove residual dust from any sanding work. Inspect the surface for any nail or screw heads protruding from the surface. These will easily crack the thinset layer you are about to lay.

Step 4

Set any nails or screws flush with or just below the tile surface with a hammer, nail set, drill or screwdriver. Wipe away any dust with a tack clot.h Once the plywood is completely clean and flat, you can lay your thinset.


Plywood and the flooring to which it is attached must be at least 1 1/8 inch thick to support the weight of thinset and tiles. Only exterior-approved plywood will support the weight; interior plywood and particleboard do not have the same strength and will buckle under the tiles.


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