How to Build a Countertop Mortar Bed

Measure the cabinet length and width with a tape measure. Mark the measurements onto a sheet of 3/4-inch plywood with a pencil, and cut the plywood with a circular saw to fit.

Place the plywood over the cabinet, and make sure the plywood is level using a carpenter’s level. Level the sheet by placing wood shims beneath low areas directly above the corners in the cabinet. Secure the plywood in place by driving wood screws through the cabinet frame and any wood shims into the plywood sheet from beneath the cabinet frame top, at the corners of the cabinet.

Mark any areas for cutouts to accommodate fixtures such as faucets or sinks, using templates provided by the fixture manufacturer. Trace the shape of the cutout onto the plywood. Cut through the plywood with a jig saw along the traced lines.

Roll a layer of roofing felt over the plywood sheet. Extend the edge of the felt up the wall three-quarters of an inch and secure it in place against the wall with a strip of masking tape. Staple the roofing felt into place at the corners and around the cutouts using the heavy duty stapler, stretching the felt taunt. Mark the position of the cutouts on the felt with a piece of chalk and then cut through the felt with a utility knife.

Place a layer of 2.5 lb. wire mesh over the felt, positioning it one-half inch from the wall and the front of the plywood. The gap ensures that no mesh is exposed to the air after placing the mortar. Use tin snips to cut the mesh to fit the space, and then place the mesh onto the felt. Mark the cutout positions with the chalk and staple the mesh in place every 6 inches.

Cut a strip of wood one-quarter inch thick and 1 1/4 inch in height to the measured length of the counter top. Attach the strip to the front of the plywood with 1 1/2 inch galvanized screws so that it rises one-half inch above the plywood surface. The strip serves as a form for the mortar bed.

Create the mortar mix by combining one part Portland cement with one part lime and seven parts sand. Add water to the mix until it’s thick but spreadable with the trowel.

Spread the mixed mortar over the wire mesh, pushing firmly against the surface to embed the mortar through the mesh and onto the felt. Build up the mortar to the top of the wood strip, spreading the mortar over the top of the strip as well, and over the edges of the marked cutouts about one-half inch.

Mix a second batch of mortar consisting of one part Portland cement, one part lime and four parts sand. Add water to the mix until it clumps in your hand when squeezed and holds together when released. Cover the first mortar layer with this mixture to build up an additional one-quarter inch deck for the tile placement. Level the mortar using the trowel, verifying its level with the carpenter’s level. Wait 24 hours for the mortar to dry, and then cut the felt openings for the cutouts with the utility knife before placing the tiles.