Finishing
What the domain tests
Finishing tests plaster, render, screed, paint, tiling, joinery finishes, surface preparation and common defects.
Core rules
- Internal plaster is commonly about 13 mm in two coats; external render is thicker and needs a scratch coat and curing.
- Prepare surfaces: clean, remove loose material, dampen as required and use a bonding agent where specified.
- Paint systems usually need primer, undercoat and finish coat; observe coverage and recoat times.
- Tiles should be bedded with adhesive or mortar, not dot-and-dabbed; use spacers and grout after the adhesive has set.
- Common defects include crazing, blowing, efflorescence and poor adhesion; find the cause before repairing.
Worked example
A wall is 8 m x 3 m = 24 m². Subtract a door of 2 m², leaving 22 m². Paint covers 12 m² per litre. Two coats need 44 m² of coverage, so 44/12 = 3.67 L. Buy 4 L. Reasoning: area x number of coats divided by coverage gives litres.
Traps
- Painting a damp wall before the cause is fixed.
- Applying thick plaster in one coat.
- Skipping primer on porous or previously painted surfaces.
- Grouting tiles before the adhesive has set.
- Ignoring efflorescence instead of treating the salt source.