How to Tile a Bathroom Floor: Planning, Mortar, Grout and Sealing
Lay out, set, grout and seal a porcelain bathroom floor with the right mortar, levelling clips and sealant, with quantities you can measure before ordering.
A tiled bathroom floor fails or succeeds underneath the tile. Large-format porcelain over a flat, stiff, dry substrate with the correct mortar and full coverage will outlast the fixtures around it. The same tile over a bouncy subfloor, a thin bed of the wrong mortar or a floor that was never flattened will crack at the grout lines within a season. This plan spends most of its time on the floor you cannot see once the job is done.
Decide the layout before a bag of mortar is opened. Bathrooms are small, so a cut sliver along the most visible wall shows immediately. Dry-lay a row in each direction from the doorway, shift the starting line so cuts at the two walls are similar and at least a third of a tile wide, and keep whole tiles at the threshold where the eye lands first.
Ontario basements and ground-floor bathrooms over slab need a moisture check and a crack-isolation or waterproofing membrane. Wood-framed floors need enough stiffness for the tile size: large-format porcelain demands less deflection than a small mosaic. When the floor flexes underfoot, fix the structure first or choose a different finish.
Measure the project
Multiply room length by width in feet, then subtract the vanity footprint only if it stays. Add 12% waste for straight layouts and 18% for diagonals or rooms with many jogs.
Divide the area including waste by the coverage of one tile. A 12 x 24 in tile covers 2 sq. ft.; a 24 x 48 in tile covers 8 sq. ft. Buy one carton beyond the count so future repairs match the batch.
A 50 lb bag of large-format mortar covers roughly 40 to 50 sq. ft. with a 1/2 in square notch, less when back-buttering. Round up, and buy a bag for the membrane bond if one is used.
A 10 lb bag of Mapei Ultracolor Plus FA grouts about 60 to 90 sq. ft. of 12 x 24 in tile at a 1/8 in joint. Wider joints and smaller tiles use more; the bag label carries the full table.
Check with a straightedge: no more than 1/8 in deviation over 10 ft for tile with any side longer than 15 in. Fill lows with self-levelling underlayment before setting.
Shop the material list
Choose products that match the exact room conditions and manufacturer instructions. These catalogue picks give you a practical starting point.
Have these ready
- Tape measure and chalk line
- 6 ft straightedge or long level
- Tile cutter or wet saw
- Angle grinder with diamond blade for notches
- Mixing drill and paddle
- Two 5 gal buckets
- Margin trowel
- Rubber mallet
- Knee pads
- Grout sponges and clean water
- Microfibre cloths for haze
- Caulking gun
- Eye protection, gloves and a dust mask for cutting
Build it in the right order
Strip the room to a sound substrate
Remove the toilet, baseboards and any old flooring down to plywood or concrete. Pull every staple and set proud nail heads. Vacuum, then check the floor with the straightedge in several directions and mark the low spots with a pencil. Confirm the subfloor is at least 1-1/8 in of plywood or that the slab is dry and free of curing compounds.
Flatten and prime the substrate
Prime the floor as the underlayment manufacturer requires, dam the doorway and drain openings, then mix and pour self-levelling underlayment into the marked lows. Work quickly; most products are workable for 15 to 20 minutes. Let it cure for the stated time before walking on it or setting tile.
Install the membrane where the room needs it
Over slab, over seams or anywhere a crack could telegraph, bond a crack-isolation or waterproofing membrane with the mortar the membrane maker specifies. Roll out the sheet, embed it with a float, and seal overlaps and the perimeter as directed. Keep the membrane clean and let its mortar set before tiling.
Snap the layout lines and dry-lay a cross
Find the centre of the doorway and snap a line to the far wall. Snap a perpendicular line using the 3-4-5 method. Dry-lay tiles with spacers along both lines and adjust the start so cuts at opposite walls match and no cut is less than a third of a tile. Mark the final lines and the first tile position clearly.
Mix mortar and set the first quadrant
Mix the mortar to the stated water ratio, let it slake and remix. Spread a thin burn coat with the flat side, then comb straight ridges in one direction with the notched side. Back-butter each large tile with a thin coat, set it with a slight slide perpendicular to the ridges and press firmly. Lift one early tile to confirm 95% coverage with no voids under the corners. Place clips at every joint and seat wedges as you go.
Cut and fit the perimeter and fixtures
Measure each cut in place, allowing for the grout joint and a small gap at the wall for movement. Score and snap straight cuts; use the grinder for notches around the toilet flange, door casing and plumbing. Set cuts in the same bedding thickness as the field tile so the surface stays flat. Clean mortar out of joints before it hardens.
Grout after the mortar has cured
Wait the mortar maker’s full cure time, then remove the clips by knocking them along the joint. Mix grout in small batches, pack it diagonally with the float, and sponge after the stated wait with a barely damp sponge, rinsing often. Work small areas; fast-setting grout waits for nobody. Buff the haze with a dry cloth once the surface dulls.
Seal and finish the movement joints
After the grout cures, apply grout sealer along each joint and wipe excess off the tile. Run 100% silicone at the tub, wall and vanity junctions instead of grout; these joints move and grout there will crack. Reinstall the toilet with a new wax or waxless seal on a flange sized for the new floor height, then refit baseboards and shoe moulding.
Common mistakes
Tiling over a floor that flexes
Deflection cracks grout and then tile. Add plywood or blocking, or choose a smaller tile, before any mortar is mixed.
Skipping the flattening step
Large-format tile shows every hump as lippage. Self-levelling underlayment is cheaper than a redo.
Spot-bonding with dabs of mortar
Five dabs leave hollow corners that crack under a dropped bottle. Comb full ridges and back-butter.
Grouting the change-of-plane joints
Where floor meets tub or wall, the joint must be silicone so it can move without cracking.
Washing grout with too much water
A soaking sponge pulls pigment and cement out, leaving weak, blotchy joints. Wring the sponge nearly dry.
Project FAQ
Can I tile over the existing vinyl or tile?
Sometimes, if the old floor is sound, flat and fully bonded, and the mortar maker approves it. Height at the door and the toilet flange usually make removal the better choice.
Do I need a membrane under bathroom floor tile?
Over concrete, over subfloor seams or in any room where water can pool, a crack-isolation or waterproofing membrane protects the tile from substrate movement and the structure from leaks.
How long before I can walk on the floor?
Most standard mortars allow light foot traffic after 24 hours and grouting after the same period; rapid-setting mortars shorten this. Follow the bag, not a general rule.
Sanded or unsanded grout?
Mapei Ultracolor Plus FA replaces both and is rated for joints from 1/16 to 3/4 in, which covers nearly every floor layout.
Does the toilet flange need to be raised?
The flange should sit on top of the finished floor. If the new tile raises the floor, use a flange extender rather than stacking wax rings.