How to Replace Mortar Beds With Plywood

Rent an electric jackhammer from your local tool rental store. These are less expensive than air-powered jackhammers and are user-friendly. Break up the mortar bed from the concrete surface. The mortar bed is generally 4 inches thick and separate from the concrete.

Scoop the broken mortar bed up with a flat shovel. Rub the shovel along the subsurface to which the bed was attached to remove any remaining mortar residue. Sweep the remaining concrete surface clean with a broom.

Measure and mark the concrete subfloor, placing pencil marks 16 inches apart on opposite sides of the concrete floor. Snap a chalk line along the floor, connecting the 16-inch interval marks.

Place treated 2-by-4 boards flat onto the chalk lines, aligning the lumber centers with the chalk lines. Drill through the lumber and into the concrete with a hammer drill and a 6-inch concrete drill bit that is 1/4-inch in diameter. Begin with the holes 6 inches off of the end of the lumber, and space them 3 feet apart along the board.

Attach the lumber to the concrete with 3/16-inch concrete screws that are 4 inches long. Drive the screws through the lumber and into the concrete with the hammer drill fitted with a screw-head bit.

Lay 3/4-inch plywood over the lumber, with the length of the plywood (4-by-8 feet) crossing the lumber rather than running along the lumber. Attach the plywood to the treated lumber with 2-inch wood screws, spacing the screws 12 inches apart along the perimeter of the plywood and throughout the center. Stagger the plywood so that the end of previous rows of plywood land in the center of subsequent rows.

Cut the plywood when you reach areas of the floor that are less than one sheet. Measure and snap chalk lines along the plywood. Place the plywood on saw horses, and cut it with a circular saw. Slide the cut plywood in place, making sure it is staggered, and attach with 2-inch wood screws.