Step 1
Sand the surface of the bare wood countertop using an electric sander with a medium-grit sanding belt. Move the sander in long, even motions to smooth down any areas of roughness or bulging.
Step 2
Place a carpenter's level on top of the countertop to see if the surface is level. If the surface remains uneven or lopsided, continue sanding until the level shows that the countertop is even across the entire surface.
Step 3
Clean the countertop and surrounding areas using a vacuum with a brush attachment. This will eliminate any sawdust and debris from the area that could inadvertently cause an uneven surface.
Step 4
Spread a 1/4-inch thick layer of mortar evenly over the entire surface using a trowel. Run a mortar rake across the mortar to scratch the layer, which will ensure that the mosaic tiles will remain secure against the countertop.
Step 5
Press mosaic tiles halfway into the mortar, spacing each mosaic tile 1/8 inch apart. Cover the entire area. Place a carpenter's level over the tile countertop. If the counter is to high in a certain area, lightly press the individual mosaic tiles in that area further into the mortar until the countertop is level. Allow the mosaic tiles to set in the mortar for 12 to 18 hours.
Step 6
Spread a 1/4-inch thick layer of fine grout over the tiled surface with a trowel, then scrape off the excess grout using the trowel.
Step 7
Wipe a damp sponge over the edges of the mosaic tiles to make the edges smooth.
Step 8
Wipe off the mosaic countertop using a damp sponge to remove the grout from the surface of the individual mosaic tiles. Allow the countertop to dry for 18 to 24 hours before use.