Check if a wall is level and flat
10 minutes — before tiling, not after
Crooked tiles are usually caused by crooked walls, not crooked tiling. This 10-minute check tells you what you are working with before a single tile goes up.
Last updated: June 2025
Only basic tools needed — most homes already have them.
Part of the Bathroom Renovation project
This is a Phase 3: Wall Prep skill in the full bathroom renovation walkthrough.
If you're renovating your bathroom, start here →Before you start
Do this check after filling and sanding, but before priming or applying tile adhesive. Filling changes the wall surface and any deviations should be assessed on the finished plaster or filler, not the bare wall.
You need a spirit level at least 600mm long for meaningful readings. A pocket level is too short to show gradual deviations across a wall.
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Tools & materials
- ✓Spirit level (600mm minimum)— longer is better — a 1.2m or 1.8m level shows gradual deviation
- ✓Tape measure— to measure the gap between level and wall
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Check the wall is plumb (vertical)
Hold a spirit level vertically against the wall surface in several positions — near each corner, in the middle, and at different heights. Note which direction the bubble moves and by how much. A wall that leans forward or backward will make vertical tile grout lines appear to splay outward from the floor as you work upward. Why: tiles are flat and rigid — they cannot flex to follow an out-of-plumb wall. If the wall leans, the tile joints at floor level and ceiling level will be different widths on the same tile. A 5mm deviation over 2 metres is visible to the eye once grouted.
Most people get this done in under 5 minutes.
Where beginners go wrong
Skipping this check entirely. "The wall looks fine" is not the same as the wall being within tolerance. A wall can look flat to the eye but have a 6mm bow that makes every horizontal tile line curve — visible only once tiles are on and it cannot be undone.
Using a short spirit level. A 200mm pocket level will read level on a bowed wall if you put it in the right place. You need at least 600mm, ideally longer, to pick up gradual deviations across a full wall surface.
Trying to compensate with adhesive bed thickness alone. Adhesive can take up to 3mm of variation. Beyond that, the thick areas have reduced bond strength and the thin areas may crack tiles. Fix the wall first.
When to call a plasterer
Deviations greater than 8–10mm over 1.8m — this needs a render or skim coat, not adhesive compensation
A wall that is significantly out of plumb across its full height — re-rendering will correct the plumb, adhesive cannot
Recommended starter kit
Five tools that cover most home repairs.
- →Adjustable spannerAmazon·Screwfix
- →Screwdriver setAmazon·Screwfix
- →PTFE tapeAmazon·Screwfix
- →Spirit levelAmazon·Screwfix
- →Tape measureAmazon·Screwfix
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What you just learned
You can now assess a wall surface before tiling — measuring plumb, level, and flatness, recording the worst deviations, and deciding whether to tile direct, fill and skim, or call in a plasterer. This is the check that prevents expensive rework.
This unlocks: