Installing Backerboard - Cutting Backerboard
To avoid cracking, tile needs a stable bed such as backerboard. The bed begins with a lather of wet mortar applied to the floor. The backerboard is set in the mortar while it's still wet, then screwed to the subfloor. Any gaps between sheets of backerboard and the floor are taped and mortared. Once this has dried, a layer of mortar is set on top of the backerboard and the tiles are set in it. Use only backerboard tape on the joints. Backerboard screws are also a must.
- LAY OUT THE PANELS
- PREPARE THE MORTAR
- MIX THE MORTAR
- MORTAR THE SUBFLOOR
- BED THE BACKERBOARD
- FASTEN THE PANEL
- INSTALL THE SECOND PANEL
- LAY THE REMAINING PANELS
- MORTAR THE JOINTS
- TAPE THE JOINTS
- MORTAR THE TAPE
LAY OUT THE CUT
Lay out the cut. Measure and lay out each end of the cut with a felt-tip pen or with a carbide scoring tool. Draw a line on each side of the panel. Use a straightedge to guide the carbide scoring tool along the layout line. Score several times with moderate pressure on one or both sides of the panel, depending on the manufacturer's instructions.
SNAP THE PANEL
Snap the panel. After scoring, press down with your hand and knee near the score line. Lift the edge to snap the panel. Cut through the backside if you haven't yet scored it.
LAY OUT THE HOLE
Lay out the hole. Measure and lay out the center of the hole. Or if you and a helper can manage the board fairly well, you can mark the hole with lipstick. Rub some lipstick on the stub of the pipe (or other obstruction), then carefully align the backerboard above it. Lower the backerboard gently onto the stub to make a mark where you'll need to drill. For best results, use one method and double-check it with the other.
DRILL THE BACKERBOARD
Drill the backerboard. Drill the hole with a carbide-tipped hole saw. Drill slowly and press lightly to avoid cracking the panel. Cut only about halfway through then turn the piece over to finish cutting the hole. The drill bit in the center of the hole saw is longer than the cutting arm itself, so when you flip the board you'll see the hole to use as a guide to finish the cut. Wear safety glasses and a respirator to avoid inhaling crystalline silica, which is harmful to lungs.
CUT LARGE HOLES
Cut large holes. If you need to cut a large hole, start by laying it out on the panel. Put a 1/2-inch-diameter carbide bit in your drill, and drill a series of holes as close together as possible just inside the layout line. (Instead of drilling, you can drive a screwdriver through the surface along the layout line.) When you've made all the holes, knock out the waste piece with a hammer. Wear a respirator and safety glasses.
LAY OUT THE PANELS
Lay out the panels. Plan the layout so the backerboards span the joints in the subfloor and reinforce them. Start every other row with a half panel so the corners of panels never meet. Snap chalklines to show where each panel will go.
PREPARE THE MORTAR
Prepare the mortar. Use latex-modified thinset mortar. Mortar has a working time of about 2 hours once it’s mixed, so mix about half the bag following the manufacturer’s directions. Start by putting the water (or the recommended liquid admix) in a large bucket and have a helper slowly pour in the mortar.
MIX THE MORTAR
Mix the mortar. As your helper pours in the mortar, mix with a paddle specifically designed for mortar-don’t use a paint paddle. The paddle has a lot of work to do, so the shank is ½ inch in diameter, and you’ll need a drill with a 1/2 –inch chuck to power it. Mix slowly to a smooth paste consistency. The mortar is properly mixed when you can form a ridge in it with a trowel. If the ridge slumps, add more mortar to the mix. If it crumbles, add water. Once it’s mixed, let it slake, or rest, for about 10 minutes, then mix again.
MORTAR THE SUBFLOOR
Mortar the subfloor. Pick the best spot to start your installation and cut a panel to fit within the layout lines, if necessary. Apply mortar within the layout lines for the panel, using a ¼-inch square-notched trowel. (The notches control how much mortar you apply.) Follow the backerboard manufacturer’s spec when choosing a trowel. Press the mortar into the plywood with the face of the trowel, holding it at a slight angle, then start building the bed. When you’ve applied a bed about 3/32 to 3/16 inch thick (depending on the manufacturer), hold the notched edge 45 degrees to the subfloor and rake out the mortar.
BED THE BACKERBOARD
Put the backerboard in the mortar bed as soon as you’ve laid the bed. Put spacers at the wall to leave a gap between the walls and the backerboard. (The size of the gap varies depending on the manufacturer.) Walk gently on the panel to set it in the mortar. If you don’t put the panels into a wet mortar bed, gaps between the floor and the panels will form in some places, and the tiles will crack when you walk over the voids.
FASTEN THE PANEL
Fasten the panels to the floor with 1 1/4-inch backerboard screws. Place the screws across the face of the panel as recommended by the manufacturer, and drive the heads flush with the surface. Keep screws at the perimeter of the panel V2 inch away from the edge, spacing them as recommended by the manufacturer.
INSTALL THE SECOND PANEL
Apply mortar within the lines for the second panel just as you applied it for the first. Put the panel in place, using spacers at the wall to leave the proper gap. Leave a 1/8-inch gap between panels using 16d nails as spacers-you'll fill the gap with mortar later to tie the panels together. Screw the panel in place.
LAY THE REMAINING PANELS
Work your way around the room spreading mortar, laying panels and screwing them in as you go. Continue to leave 1/8-inch gaps between panels and a 1/4-inch gap at the wall. Remove the spacers once the panels are installed.
MORTAR THE JOINTS
When you've laid all the panels, fill the spaces between them with mortar. Smooth it on with a margin trowel, forming a 3-inch-wide band that's centered on the joint.
MORTAR THE TAPE
Apply the mortar, then smooth it out with a trowel. You won't be able to get it flat without exposing the tape, so simply smooth the mortar with the trowel. Feather the edges. When the mortar has dried, lay out the floor.
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Skill Level: Beginner
Time: 1 hour
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