Can You Put HardieBacker Over Laminate Countertops?

Increased Profile

• HardieBacker and tile increase the profile of the countertop. Plumbing and electrical components under the countertop need a bit of slack to fit properly once they are reconnected to sinks and drop-in stovetops. Wiring and water supply lines are usually long and flexible enough to accommodate the additional countertop thickness, but the drain pipe may require replacement. Disassembling the curved p-trap and pipe will reveal whether there is enough excess length of pipe at the connections to extend the assembly. Some pipes are trimmed when they are installed, so there may be no excess. PVC replacement pipes with glueless compression fittings are inexpensive and simple to install. Gauge the surplus wiring and plumbing length needed by measuring the thickness of the HardieBacker and tile and add approximately 1/8 inch for the tile adhesive and mortar bed.

Primary Cuts

• HardieBacker features an embossed grid on the surface, which helps you measure and cut it straight. Measure the depth of the countertop, from the wall to the front edge, and apply that measurement widthwise to the HardieBacker with a pencil. Measure the length of the countertop and mark the sheet accordingly. You will need at least two sheets to cover long countertops. Measure the thickness of the countertop, and cut strips from the remaining HardieBacker to fasten across the front and side edges, perpendicular to the top of the counter. Never cut tile underlayment with rotary tools or other power cutters, as they will release hazardous silica dust into the air from the sheets. A utility knife is sharp enough to score or make a shallow cut across the sheets, allowing you to break them at the scored line.

Detail Cuts

• Sinks and other set-in items require openings through the HardieBacker, and the existing countertop is an ideal template. After disconnecting and removing the items, lay the HardieBacker sheets on the countertop, aligned with where you will fasten them. Open the cabinet doors to access the underside of the countertop and trace the perimeter of the openings onto the bottom of the underlayment with a pencil. Cutting the openings while the sheets are in place will drop debris inside the cabinets, so move them to another work area after you trace the outlines. Scoring around, then across the center of the traced outlines, similar to cutting a pie, lets you tap out the material with a hammer.

Fastening

• Acrylic or latex modified thinset mortar, which is also used to set tile, helps bond HardieBacker to the laminate. Spread thinset on the laminate with a notched trowel, then set the sheets in place and press them down into the mortar bed. Three-quarter-inch, countersinking, corrosion-resistant screws are the recommended fasteners, but they should not protrude through the underside of the countertop. Exposed screw tips can cut your hands when reaching inside the cabinet. HardieBacker has embossed marking that show proper screw placement, but trimming the sheets may place some screw marks too close to the edges. Keep perimeter screws 2 inches from the edge to prevent cracking the underlayment.

Bridging Seams

• Bridging and sealing the seams between HardieBacker sheets guards against water seepage. Spread a thin layer of latex or acrylic-modified thinset mortar along both sides of the seams, then press 2-inch-wide, fiberglass mesh seam tape into the mortar. Scraping off the excess mortar with a trowel or putty knife removes bumps and ridges, flattens the tape and leaves the countertop with an even, water-resistant surface for the tile.