Surface Preparation and Setting-Out
The exam tests whether you can hand over a substrate that will hold tiles for years, and set out a layout that produces balanced cuts instead of a 20 mm sliver in a doorway.
Substrate rules
- Clean, sound, dry and flat: remove paint, old adhesive, dust, oil and loose screed.
- Prime porous substrates and dusty concrete; follow the primer's dilution.
- Respect curing and moisture: new concrete and screed must be dry and cured before tiling.
- Check flatness against the specification with a straightedge; grind high spots and fill hollows with patching compound - never with extra adhesive.
Setting out
- Establish a datum and find the room's centre lines. Square them with the 3-4-5 method (for example 1.2 m, 1.6 m, 2.0 m) or a laser.
- Dry-lay a row in both directions before mixing anything.
- Design the cuts: aim for half-tile or larger at the edges, full tiles at the main sight line and the entrance, and check door thresholds, sanitaryware and expansion joints.
- Snap chalk lines and check the diagonals; a grid with equal diagonals is square.
Worked example
A 3.6 m × 4.8 m floor, 600×600 tiles, 3 mm joints, centred layout. Along 4.8 m: 8 tiles + 7 joints = 4,821 mm, so 21 mm over - two edge cuts of about 589.5 mm. Along 3.6 m: 6 tiles + 5 joints = 3,618 mm, so two cuts of about 591 mm. Both edges are close to full tiles, no slivers, and the centre lines remain the setting-out grid.
Traps that cost marks
- Setting out from a wall that is out of square or out of plumb.
- Forgetting joint width in the arithmetic.
- Tiling over a dusty or unprimed floor.
- Levelling a hollow with adhesive instead of patching compound.