Laying A Tile Floor

MATERIALS: One quarter or 1/2-inch backerboard, backerboard screws, thinset mortar, latex primer, self-leveling mortar tiles, grout, grout sealer, fiberglass tape

TOOLS: Level, framing square, tape measure, straightedge, chalk line, carbide backerboard cutter, mortar mixing paddle, screw gun, drill, tile cutter or tile saw, safety glasses, grout bag, grout float, margin trowel, notched trowel, sponge, soft cloth, nonabrasive scouring pad, rubber gloves, foam paintbrushes, tile nippers

WHAT IT TAKES FOR TILE - To make sure your joists will support the tile floor, look at the nailing pattern. If the rows of nails are spaced 16 inches or less, you're fine; if not, you'll have to add support or put in another kind of floor.

Tile is a layered floor. Underneath those fancy tiles that you so carefully chose is a dull gray base that carries all the weight. Without it, the floor would flex, the tiles would crack, and the grout between them would pop out. The base is backerboard, a rigid panel that, depending on the manufacturer, is composed of cement, fiber cement, gypsum, plywood, or plastic that provides a sound substrate for setting tile. It sits in a thin coat of wet mortar and is screwed to the floor or wall underneath. It’s sometimes referred to as “mason’s drywall”.

Some companies make a mastic that you can use to stick tiles to a plywood subfloor, but most tilers are against using it. When you’re tiling, mortar over a recommended backerboard results in a far superior bond and a more rigid base. In short, the tiles stick better and won’t crack. Once the base is down, laying the tiles is a matter of spreading mortar and putting the tiles in place. The mortar is called “thinset” not because it’s runny, but because you can use a thinner layer than with older products. Thinset mortar is plenty strong, so don’t be tempted to use an epoxy mortar; epoxy is for pros who can work quickly and neatly.

GET THE RIGHT ADHESIVE - Mortar is a combination of sand and cement, which dries hard and holds the tile in place. (Grout, which you apply between the tiles, is made of the same materials, but because the proportions are different, you can't substitute one for the other.) The mortar used to set tile is called thinset—not because it’s thin, but because you install a sheet of precast concrete as a subfloor, instead of laying a thick mortar base in advance of the mortar that holds the tile. Use a latex-modified thinset, which results in a stronger bond, especially with porous tiles. With light and translucent tiles, make sure you use white thinset, as gray may show through. Both marble and granite stain easily so use a mortar especially designed for use with them. Most mortars are made for both wall and floor use. Some (usually containing lime for extra strength) are specifically for walls. Buy a mortar designed for floor, or floor and wall, use.

MAKE A FLOOR PLAN. Draw the walls of the room as accurately as you can on a sheet of grid paper. Include doorways and floor obstructions such as cabinets and fixtures. Grid paper is available with 1/8-inch grid spacing. For greatest accuracy, draw your plan as large as possible on the page. Mark dimensions and your scale.

Laying backerboard

1 CHECK TO SEE WHETHER THE FLOOR ON WHICH THE TILE WILL GO IS FLAT. To do this, put a straightedge on the floor, and look for gaps between it and the floor. Mark gaps on the floor; clean the area and paint it with a latex primer. Pour self-leveling mortar over the area, then feather the edges with a straightedge.

2 SNAP CHALK LINES ON THE FLOOR TO SHOW WHERE THE SHEETS OF BACKERBOARD WILL GO. Arrange the sheets so that the ends are staggered. If some sheets need to be cut to fit, lay out the cut on the backerboard. Score along the line with a carbide backerboard cutter guided by a straightedge. If recommended by the manufacturer, score both sides. Press down with your hand and knee on one side of the line, and lift the opposite edge to snap the panel.

PRESETTING SCREWS MEANS FASTER DRIVING - Most of the time required to drive backerboard screws is taken up by fumbling in your work apron for the screws. Although the screws pull themselves into the panel once the threads engage, they have a hard time penetrating the rocklike surface. You will find it much faster to preset the screws by tapping them through the surface with a hammer. You can cut the time in half again by giving the presetting operation to a handy assistant.

3 A LAYER OF MORTAR UNDER THE BACKERBOARD HELPS TO KEEP THE BOARD FROM FLEXING and is an important part of the installation. Mix mortar according to the directions on the bag. Spread mortar on the floor where your first sheet of backerboard will go. Once it's spread, comb it out with the notched edge of the trowel, holding the trowel at about a 45-degree angle to the floor.

4 PUT THE FIRST SHEET OF BACKERBOARD IN PLACE AND SCREW IT DOWN with backerboard screws placed every 4 inches. (Use 1 1/2-inch screws for 1/2-inch board and 1 1/4-inch screws for 1/4-inch board. Do not screw directly into joists.) Spread mortar for the next sheet; put the sheet on edge against the previous sheet and pivot it down into the mortar. Leave a 1/8-inch gap between sheets, and screw each board as you go. At the corners, keep the screws 2 inches from the edge to avoid cracking it. (If directed by the manufacturer, use a screw gun with a clutch.)

5 LAY THE REST OF THE BACKERBOARD SHEETS. Fill the spaces between them with thinset mortar and a margin trowel. Reinforce by covering the gap with fiberglass tape, embedding it firmly in the wet thinset. Cover the tape with a second layer of thinset. Feather the edges with the trowel to create a flat surface.

Laying out the floor

1 MEASURE FROM BOTH ENDS OF THE LONGEST WALL OUT SEVERAL TILE SPACES (allowing a 1/4-inch gap at the wall) and mark with pencil.

2 SNAP A CHALK LINE BETWEEN THE TWO POINTS JUST MARKED. This line should represent the center of one of the tile joints.

3 REPEAT STEP 1 FOR THE NEXT LONGEST ADJACENT WALL, and snap a second chalk line. This line also will represent the center of a tile joint.

4 CHECK THE ANGLE BY MARKING POINTS 3 FEET AND 4 FEET FROM THE INTERSECTION. Measure the diagonal. If it is exactly 5 feet, your lines are squared. If not, repeat the first three steps.

Before you snap chalk lines on the floor, shake the line to remove excess chalk. Too much chalk makes the line muddy and hard to follow.

TEN TIMES MORE ACCURATE THAN MEASURING ASINGLE TILE AND SPACER IS MEASURING 10 TILES AND 10 SPACERS. Simply line up 10 in a row, measure the span, and divide by 10.

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