How to Tile a Bathroom Floor: Layout, Cuts and Grout

The tile is chosen and the toilet is the one fixture you only want to move once. Three things can go wrong before the first tile is down: thin-set spread straight onto a bouncy subfloor, a layout started against the tub that ends in a thin sliver at the door, and a flange left sitting below the new floor. Below are the steps in order, with each maker figure from its own document.

The short answer

Stage	What to do	Wait before the next stage
Check the floor	Joists and subfloor meet your backer’s minimums; no bounce	—
Strip the room	Toilet, baseboard and old floor out; damaged subfloor replaced, low spots leveled	—
Cover the subfloor	1/4 in cement board in mortar, fastened every 8 in; or an uncoupling membrane in modified thin-set	Tile right away on the example membrane
Lay out	Center lines, a dry row, no cut under half a tile	—
Set the tile	Notch sized to the tile; at least 80% mortar contact dry, 95% wet, so aim for 95% on a bathroom floor (our suggestion); 1/4 in gap at the walls	24 hours before grouting (example thin-set, cement-board route)
Grout	Sanded for 1/8 to 1/2 in joints, non-sanded up to 1/8 in (example grouts); caulk, not grout, at walls and tub	16 hours before foot traffic (example sanded grout); keep water off for 3 days (our suggestion)
Reset the toilet	Flange flush with or slightly above the tile	—

Is your floor ready for tile?

Movement between the floor and the tile is the major cause of cracked and delaminated tile in the membrane maker’s handbook, so check the structure before you buy anything. Everything below is for a wood-framed floor. A concrete slab is outside this article: the example backer board is not designed for use over concrete, and the membrane handbook gives concrete its own details.

Stiffness. Under the example backer board’s installation guide, the floor must be engineered not to exceed L/360 deflection (L/720 for natural stone); the example thin-set’s data sheet gives the same two limits for plywood floors. On a 12-foot span, L/360 is about 0.4 inch (our arithmetic), too little to judge by eye (our reading). If the floor bounces, you cannot confirm the joists against your local code’s span table, or a joist is cracked, notched or sistered, have a contractor or engineer look first (our suggestion).

Minimums for the layer you choose. Each maker sets its own.

Over a wood subfloor	Cement backer board (1/4 in)	Uncoupling membrane
Subfloor	At least 5/8 in exterior-grade plywood or 23/32 in OSB	At least 19/32 in (5/8 in nominal) tongue-and-groove plywood or OSB at 16 in joist spacing; 23/32 in (3/4 in nominal) at 19.2 in
Joist spacing	Up to 24 in on center	Up to 16 or 19.2 in for a single layer; at 24 in, I-joists or trusses only, with a second 11/32 in layer or the maker’s thicker XL membrane on 23/32 in

The membrane column is from the DITRA installation handbook. For ceramic or porcelain on plywood or OSB, the handbook’s 24-inch details list I-joists or trusses only; with sawn joists at 24 inches, ask the maker or an engineer (our suggestion). For tile smaller than 2 x 2 inches the handbook says to call the maker first, and natural stone requires a double-layer wood floor whatever the joist spacing.

How do you take the toilet out and the old floor up?

Have a new wax ring and closet bolts ready: never reuse the ring, and replace the bolts with it, per the wax-ring maker’s guide.

1. Turn the shut-off valve clockwise, flush to empty the tank and bowl, and sponge out the rest. If the valve will not close or leaks, that is a plumbing job before anything else (our suggestion).
2. Disconnect the supply line, take off the bolt caps and nuts, rock the toilet gently to break the seal and lift it straight up onto padding.
3. Scrape the old wax off the flange and the toilet’s outlet horn, and look at the flange for cracks, rust or damage. For a cracked flange the guide points to a flange repair kit; if the flange is broken beyond that, or the pipe under it is damaged, call a plumber (our suggestion).

Check the flange height now. Toilet flanges must sit flush with or slightly above the finished floor, in the same guide. The new floor adds about 19/32 inch over the membrane (1/8 inch mat, 3/8 inch tile, 3/32 inch of mortar) or about 23/32 inch over cement board, before the mortar under the mat or board (our arithmetic, for a 3/8 inch tile). Plan on a flange spacer or extender, or an extra-thick wax ring, and never stack two rings.

Then strip the room down to the subfloor.

1. Take off the baseboard, trim and anything else in the way (one tile maker’s guide).
2. Old flooring adhesive may contain asbestos fibers: do not sand or grind the residue, and do not sand flooring that contains asbestos, per the example thin-set’s data sheet. If you do not know what the old floor is, have it tested before you take it up, and check whether local rules require professional removal (our suggestion).
3. Check the bare subfloor, around the flange too. Soft or stained wood can mean a past leak (our reading); cut out and replace water-damaged subfloor before the backer or membrane goes down. If the damage reaches the joists or the drain pipe, call a contractor or plumber (our suggestion).
4. Replace loose, warped or damaged panels and make sure the panels are properly fastened. On the membrane route, tightly butted or tented seams must be addressed and any leveling must be done before the mat goes down. Level dips on either route now rather than filling them with thin-set, since the example one is rated for a bed of 3/32 to 1/4 inch under the tile (our reading).

Backer board or membrane: what goes under the tile?

Pick one and follow its maker’s steps; do not mix the two documents’ instructions (our suggestion).

Cement backer board

From the cement board’s guide, which recommends the 1/4 inch board for floors unless you need 1/2 inch to match a transition:

1. Plan the sheets so their joints are staggered, do not line up with the subfloor joints, and never meet four corners at one point. Leave 1/8 inch between boards and 1/8 inch at walls and cabinet bases.
2. Cut by scoring with a carbide-tipped or utility knife along a straight edge and snapping upward; for the flange opening, score around it and knock it out from the face side with a hammer. No high-speed power tools such as saws or grinders on these boards indoors, because of silica dust, and never dry-sweep the dust: clean up wet or with a HEPA vacuum.
3. Spread a bed of mortar or modified thin-set on the subfloor with a 1/4 inch square-notched trowel (unmodified dry-set mortar is allowed for this layer only) and press the board into it while it is wet. Use a mortar whose data sheet lists your subfloor (see membrane step 1 for the example thin-set’s limits).
4. Fasten every 8 inches over the whole board, 3/8 to 3/4 inch from the edges and 2 inches from the corners, heads flush and not overdriven. For interior floors the guide lists corrosion-resistant roofing nails or No. 8 ribbed wafer-head screws, at least 1-1/4 inches long.
5. Fill the joints with the same mortar you will set the tile in and embed 2 inch alkali-resistant glass-fiber tape over them.

Tile on this board goes in a latex- or acrylic-modified thin-set meeting ANSI A118.4.

Uncoupling membrane

From the membrane handbook for DITRA, a 1/8 inch thick plastic mat with a fleece underside:

1. Bond it with a thin-set suited to the subfloor, which on wood means a latex-modified thin-set in the handbook; pre-mixed thin-sets and mastics are not suitable with this membrane. Check that your mortar’s data sheet lists your subfloor and room: the example all-purpose thin-set is not to be bonded directly to OSB, and lists plywood for dry areas only.
2. Burn a thin coat into the subfloor with the flat side of the trowel, then comb more on with the notched side: the maker’s 11/64 inch square-notch DITRA trowel, a 1/4 x 3/16 inch V-notch or a 5/16 x 5/16 inch V-notch.
3. Lay the mat fleece side down and press it in with a float or roller before the mortar skins over.
4. Lift a corner. The fleece should be in full contact with the mortar; if not, pull it up and reapply. Butt the sheets edge to edge.
5. Tile can go on straight away, in unmodified thin-set (ANSI A118.1) or the maker’s own mortars, not another maker’s modified thin-set: sandwiched between mat and tile, those dry slowly and can need long cures before grouting.

Where a floor has to be waterproof, the handbook adds a step: seal the seams and the floor-to-wall joints with its banding tape, lapped at least 2 inches onto the mat.

How do you lay out the tile so there are no slivers?

From one tile maker’s floor tile guide:

1. Mark the center point of each wall, snap chalk lines between opposite walls, and make sure they cross square.
2. Dry-lay a row of loose tiles along each line with spacers in the joints.
3. If a row leaves cuts smaller than half a tile at the walls, snap a new line half a tile closer to one wall and check again.
4. Snap lines parallel to the center lines to split the floor into grids of about 2 by 3 feet.

A worked example. A floor 60 inches across, 12 inch tiles, 1/8 inch joints, a 1/4 inch gap at each wall. With a joint on the center line, two full tiles each side leave about 5-7/16 inch cuts at both walls, under half a tile. Move the line 6 inches, so a tile is centered on it, and each wall gets an 11-1/2 inch cut (our arithmetic). Check the other line the same way, and put the larger cut at the doorway (our suggestion).

Rectangular tile. In the same tile maker’s guide, rectangular porcelain should never be set in a running bond (a half offset, our reading): offset it by no more than a third, widen the joint to 3/16 inch and use a large-unit porcelain mortar.

Door jambs. Undercut the jambs so the tile slides under them instead of being notched around the trim.

Which trowel do you need, and how much mortar?

The notch depends on the tile size. One tool maker’s trowel chart pairs them like this, with the note to follow the mortar maker’s notch recommendation first:

Tile	Notch	Mortar
Up to 8 in	1/4 x 1/4 x 1/4 in square	Thin-set
8 to 16 in	1/4 x 3/8 x 1/4 in square	Thin-set
Larger than 15 in	1/2 x 1/2 x 1/2 in square	Medium-bed or large-format mortar
Longer than 20 x 20 in, large rectangles, thick tile (one tile maker)	Back-butter as well	Medium-bed mortar

The 8 to 16 and larger-than-15 rows overlap on the chart itself; for a 16 inch tile, go by the mortar’s data sheet (our suggestion). For large-format tile, the same tile maker requires at least 90% mortar contact, a grout joint of at least 3/16 inch and a level substrate.

How much. A 50 lb bag of the example thin-set covers 85 to 95 square feet with a 1/4 inch square notch and 60 to 67 with a 1/4 x 3/8 inch notch, so a 40 square foot floor of 12 inch tile on cement board takes about two-thirds of a bag for the tile and under half for the bed under the board. Over the membrane, the handbook gives a bag per 150 square feet to bond the mat and per 40 to 50 square feet to set tile with a 1/4 x 3/8 inch notch: about one bag of unmodified thin-set for the tile (our arithmetic, both routes).

How do you set the tile?

Wear protective gear when handling the thin-set and grout: impervious gloves such as nitrile, safety glasses and a NIOSH N95 respirator on the example grout’s data sheet, and chemical-resistant gloves and a NIOSH-approved respirator on the example thin-set’s. The mixing ratio, temperature and timings below are the example thin-set’s, for the cement-board route. On the membrane, use unmodified A118.1 thin-set or the membrane maker’s mortar, mixed and timed per its bag.

1. Keep the room warm. Between 50°F and 100°F for 72 hours with the example thin-set.
2. Mix. 6 quarts of water per 50 lb bag to a smooth paste; let it stand 5 to 10 minutes, stir again, and do not add more water. Mix only what you can use within 30 minutes, and don’t spread more than you can set in 15, in one tile maker’s guide.
3. Spread one grid at a time. Skim a coat on with the flat side of the trowel, then comb ridges with the notched side at 45°, in one direction. Leave your chalk lines visible.
4. Set from the center out. Start at the corner of a grid on the center lines and work outward. Press each tile down and move it back and forth across the ridges to collapse them. The tile maker’s guide says to use a slight twisting motion and not to slide tiles into place (our reading: a short move across the ridges, not sliding the tile into position). Mix tiles from several cartons.
5. Spacers and the wall gap. Put a spacer in each joint. Fit the cut tiles at the edge of each grid last (cutting is the next section), 1/4 inch from the wall.
6. Check the mortar contact. Periodically pull up a freshly set tile. At least 80% contact is required in dry areas and 95% in wet areas, with all edges supported, on the example thin-set’s data sheet and in the membrane handbook; aim for 95% on a bathroom floor (our suggestion). If it falls short, take the tile up, scrape it, check the mortar’s consistency and your notch, and reset it. Back-buttering tiles 12 x 12 inches and larger also helps, in the handbook.
7. Bring the tiles level. When a grid is done, tap the tiles with a rubber mallet, or a hammer on a wood block, so they sit in one plane.
8. Clean as you go. Clear mortar out of the joints with a putty knife and off the faces with a damp sponge before it hardens.

Keep off the floor until the mortar has set: usually 24 hours, in the tile maker’s guide.

How do you cut tile around the toilet flange and the edges?

The tile maker’s guide gives the tools:

• Straight and diagonal cuts: a tile cutter. Measure, mark with a pencil or felt-tip pen, cut.
• The flange and other curves: tile nippers, chipping away small pieces at a time, or a rod saw for a long curved cut. Smooth sharp edges with a carborundum stone.

For the flange (our suggestion): set the tiles around it, mark the circle on the tile that covers it, cut that tile in two through the circle’s middle, and nibble a half-circle from each piece. The toilet base hides the edge.

When and how do you grout?

Wait for the mortar. On the cement-board route, 24 hours before grouting with the example thin-set, and at least 24 hours in the backer board’s guide. On the membrane route, go by your unmodified mortar’s bag; the handbook puts its final set usually within 24 hours. The example grout wants the setting mortar cured 24 to 48 hours unless it is rapid-setting. Pull out the spacers and clear any mortar left in the joints.

Pick the grout by joint width. The example sanded grout covers joints 1/8 to 1/2 inch, so it suits the 3/16 inch minimum for large-format and rectangular tile above (our reading); the non-sanded version takes joints up to 1/8 inch and suits tile that sand could scratch, such as polished stone. Before you grout, test the grout on a small, hidden area to see whether it scratches your tile. The premium Prism grout fills joints up to 1/2 inch, its coverage chart starting at 1/16 inch; one 17 lb box covers about 348 square feet of 12 x 12 x 3/8 inch tile at 1/8 inch joints, plenty for the 40 square foot example (our arithmetic).

Grout it, following the sanded grout’s data sheet:

1. Keep the room between 50°F and 100°F. Highly absorbent, porous, rough or textured tile, and some porcelain, may need sealing before grouting to prevent staining.
2. Mix 2 to 2.5 quarts of water per 25 lb bag until smooth (4 to 4.5 pints per 17 lb box for the premium grout), let it stand 5 minutes, remix, and do not add water later.
3. Dampen very absorbent tile lightly, with no standing water in the joints.
4. Hold the rubber float at 45° to pack the joints full, then at 90° to scrape off the excess.
5. At 70°F, spread no more than you can clean within 30 minutes of the grout firming up.
6. Smooth the joints and wipe off the excess with a damp sponge in a circular motion, rinsing it frequently. Wipe the haze off after 3 hours with cheesecloth or a wrung-out sponge.

Let it cure. No foot traffic for 16 hours with the sanded grout; the premium one is sold as walkable in four hours. Both want at least 72 hours above 50°F, and the premium grout’s data sheet allows intermittent water after 3 days, so keep water off the floor and don’t mop for 3 days (our suggestion). One tile maker says to wait 72 hours before heavy use.

Sealing. Optional on the example grouts: the premium one is sold as needing no sealer and can take a pH-neutral, water-based one after 48 hours of cure; the sanded one takes a penetrating sealer if you want one. One tile maker says not to apply sealers or polishes for three weeks, so wait the three weeks if you seal (our suggestion).

Finish the edges. The sanded grout is not for movement joints or changes of plane, and movement joints are required at perimeters, so the 1/4 inch wall gap and the joint against the tub (a change of plane, our reading) get caulk or sealant, not grout; the membrane handbook also calls for perimeter joints around any floor. Once the grout has cured, caulk them and refit the baseboard over the wall gap (our suggestion).

When can the toilet go back?

Once you can walk on the grout: 16 hours with the sanded grout, 4 hours with the premium one (our suggestion). Then, following the wax-ring guide:

1. Fit the flange spacer or extender if the flange now sits below the tile.
2. Put new bolts in the flange and center the new wax ring on it.
3. Lower the toilet straight down onto the bolts and press down to compress the ring evenly.
4. Tighten the nuts a little at a time, alternating sides, so the porcelain does not crack.
5. Reconnect the supply line hand-tight plus a quarter turn, open the valve, flush several times and check for leaks with a towel around the base to keep the grout dry (our suggestion). If the toilet rocks, check the flange height or shim it.
6. Caulk around the base if you want a finished look.

To float a vinyl floor instead, see how to install vinyl plank flooring. Shorter jobs are in our home improvement projects guide and the home improvement section.

Where these numbers come from

Figures come from the cement board’s guide, the membrane handbook, the thin-set and grout data sheets, the trowel chart, one tile maker’s floor guides and one wax-ring maker’s guide, read on 11 October 2026. Floor sizes and the 3/8 inch tile are our examples; cut sizes, bag counts and floor build-up are our arithmetic.

Frequently asked questions

How long after laying floor tile can you grout?

24 hours with the example thin-set on the cement-board route; the example grout wants the mortar cured 24 to 48 hours unless it is rapid-setting. On the membrane route, go by your unmodified mortar's bag. Keep the room above 50°F throughout.

Do you tile under the toilet or around it?

Under it: the toilet sits on the new tile, with only the flange opening cut out (our reading). The flange must end up flush with or slightly above the finished floor, in one wax-ring maker's guide, so a flange that sat flush with the old floor is likely to need a spacer or extender (our reading).

Do I need to seal grout on a bathroom floor?

Not with the two example grouts: sealer is optional on both, from 48 hours of cure on the premium one. One tile maker says not to apply sealers or polishes for three weeks, so if you do seal, wait the three weeks (our suggestion).