Tiling a bathroom floor is one of those jobs that looks simple until you're halfway through and realise you've tiled yourself into a corner — literally. I've been doing this professionally for over a decade and I still see the same mistakes from amateur and trade alike.
This is the method I use on every bathroom floor job. Follow it and you'll get a flat, level, properly bedded floor that lasts.
Quick summary
- Subfloor prep is the job. Everything else is just practice.
- Start from the centre — never from a wall.
- Use a flexible adhesive for any floor subject to movement or underfloor heating.
- Leave grout joints consistent: 3mm for standard tiles, 1.5mm for large format.
What You'll Need
Tools:
- Manual tile cutter (for straight cuts up to 70cm) or wet saw for anything bigger
- Laser level — a self-levelling cross-line model
- Notched trowel (6mm × 6mm square notch for standard floor tiles; 10mm × 10mm for large format)
- Rubber mallet and tile spacers
- Long spirit level (1.2m minimum)
- Angle grinder with diamond disc for awkward cuts
Materials:
- Floor tile adhesive — S1 class flexible for bathroom floors (rigid adhesive will crack with any building movement)
- Grout — unsanded for joints under 3mm, sanded for wider joints
- Primer for the subfloor (Bal primer or similar)
- Waterproof membrane or tanking kit if tiling into a wet room
Step 1: Prepare the Subfloor
This is where most DIY bathroom tiling fails. If the subfloor isn't right, no amount of skill with the tiles will save you.
Concrete subfloor: Check for cracks, loose areas, and contamination (oils, paint, release agents). Fill cracks with a flexible filler. Apply a diluted PVA primer (1:3 ratio) or a proper tile primer — I use Bal Prime AP on every job. Let it go tacky.
Timber subfloor (most UK bathrooms): This is trickier. Timber flexes. Standard ceramic tiles can crack. You have two options:
- Decoupling mat (my preference): A DITRA-style mat absorbs movement between the tile and the timber. Significantly reduces cracking risk. Worth every penny.
- Tile backer board: 6mm or 12mm Hardibacker or Jackoboard screwed at 200mm centres. Better rigidity than timber alone. Use S1 adhesive on top regardless.
Never tile directly onto standard plywood or chipboard without a decoupling mat or backer board. It will move and your tiles will crack — sometimes within months.
Check for flex: Walk the floor. Any bounce over 1-2mm at mid-span is too much. Add noggins, sistered joists, or additional board to stiffen it.
Check for level: Use your long spirit level to map high and low spots. You can skim low areas with a floor levelling compound (Mapei Ultraplan or similar). High spots need planing or grinding.
Step 2: Plan Your Layout
Never start tiling from a wall. Walls are rarely square, and starting from one will result in tiles that splay out as you go.
Find the Centre
- Measure opposite walls and mark the centre of each
- Snap chalk lines between opposite centres — you now have a cross in the middle of the room
- Lay a dry run of tiles along both lines to see where cuts fall at the edges
The rule on edge cuts: You want your smallest cut to be at least half a tile wide. If the dry run gives you a 5mm sliver at one wall, shift your centre line by half a tile. A half-tile cut looks intentional. A 5mm sliver looks like a mistake.
Account for Doorways
Check whether the floor threshold at the door will have an awkward cut. It's worth adjusting your starting point to get a cleaner look at the door opening — that's the first thing people see when they walk in.
Step 3: Mix the Adhesive
Use a slow-speed drill with a mixing paddle. Never mix by hand — you'll get lumps.
Follow the manufacturer's instructions for water ratio exactly. Under-watered adhesive won't bond. Over-watered adhesive loses strength. I use about 4.5 litres per 20kg bag for most floor adhesives, but always check the bag.
Mix until smooth, let it slake (rest) for 5 minutes, then mix again. This activates the polymers. Don't rush this step.
Step 4: Start Tiling
Spread adhesive in the direction away from your start point, covering about 1m² at a time. Use the notched trowel at 45° to create consistent ridges. You need full coverage — no voids under floor tiles, especially in wet areas.
Key technique — back-buttering: For tiles larger than 300×300mm, apply a thin skim coat of adhesive to the back of the tile as well as the floor. This ensures full contact and prevents hollow spots.
Press firmly and twist slightly as you lay each tile to collapse the ridges and ensure full bedding. Check with a spirit level every 3–4 tiles. Tap down high corners with a rubber mallet.
Keep joints consistent using tile spacers. I use 3mm crosses for standard bathroom tiles. Remove spacers before the adhesive goes off (usually 20–30 minutes) — dried-in spacers are a nightmare to remove.
Step 5: Cutting Tiles
Straight cuts: A quality manual tile cutter handles porcelain up to about 10–12mm thick cleanly. Score firmly in one pass, then snap. If you're getting ragged breaks, your scoring wheel may need replacing.
L-shaped cuts and notches: Use an angle grinder with a diamond disc, or a wet saw. Always cut away from you. Always wear eye protection.
Holes for pipes: A diamond core drill bit in a drill press or angle grinder. Mark the centre, tape the tile surface to prevent chipping, drill at slow speed with water cooling.
Step 6: Allow Adhesive to Cure
Standard floor adhesive needs 24 hours before grouting at normal room temperature. Flexible S1 adhesives can take up to 48 hours in cooler conditions. Don't rush this.
Keep the area clear of foot traffic during curing. Light foot traffic on properly cured adhesive is fine — heavy traffic, stools, or bathroom furniture should wait until after grouting and final cure (typically 72 hours).
Step 7: Grout
Choose the right grout:
- Unsanded/wall grout: joints under 3mm
- Floor grout: wider joints, higher compressive strength
- Epoxy grout: ideal for very narrow joints (1.5mm) or areas exposed to cleaning chemicals
Method:
- Mix grout to a peanut butter consistency — not runny
- Apply diagonally across the tiles using a rubber float, pressing firmly into joints
- After 15–20 minutes (when grout starts to firm), clean off excess with a damp sponge. Rinse sponge constantly
- Polish off the haze with a dry cloth once the surface is firm
Fill movement joints (perimeter gap around the room, any change of plane) with a matching silicone, not grout. Grout will crack at these joints — silicone flexes with the building.
Common Mistakes to Avoid
Not priming the subfloor. Adhesive can pull moisture from an unprimed substrate and fail to bond properly. Always prime.
Spreading too much adhesive at once. If adhesive skins over before you lay the tile, scrape it off and start again. Laying onto skinned adhesive is the main cause of hollow tiles.
Grouting too early. Adhesive that hasn't cured will continue to move slightly. Grouting over uncured adhesive can cause grout cracking within weeks.
Skipping expansion gaps. All tiled floors need a perimeter gap of 5–8mm. Fill with silicone. This is mandatory — not optional.
Ignoring datum levels. Always check your work against a datum (a fixed level reference). Without one, errors accumulate and your floor will be out of level by the time you reach the far wall.
FAQ
How long does it take to tile a bathroom floor? A typical UK bathroom (4–6m²) takes a full day for a competent DIYer: half a day for prep and layout, half a day for tiling. Add another half day for grouting after 24 hours cure.
What's the best tile size for a small bathroom? Contrary to popular belief, larger tiles (600×600mm or 600×1200mm) can make a small bathroom look bigger, not smaller. They have fewer grout lines which creates a more seamless look. The trade-off is more complex cutting around obstacles.
Do I need waterproofing under bathroom floor tiles? For a standard bathroom with a bath or shower tray: not strictly required under the floor if the shower tray is correctly sealed. For a wet room or walk-in shower with a linear drain: yes, full tanking is essential.
Can I tile over existing tiles? Technically yes, but only if the existing tiles are fully bonded (no hollow spots), the subfloor can take the added weight, and the height increase won't cause issues with door thresholds or other flooring. I'd recommend removing the old tiles where possible.
Tools I Use on Every Bathroom Floor Job
- Sigma 4BU 70cm tile cutter — handles all standard bathroom tiles
- DEWALT self-levelling laser — essential for checking levels across the full floor
- Bosch GWX 18V angle grinder — for notch cuts and pipe holes
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