Grouting, Sealing, Finishing and Repair
This domain tests finishing work: grout selection and mixing, joint filling, curing, sealing, caulking movement joints, cleaning and repair. The exam expects you to match the grout to joint width and tile type, avoid efflorescence and weak grout, and repair defects without damaging adjacent tile.
Core rules
- Use sanded grout for joints about 3 mm and wider, and unsanded grout for narrower joints, unless the manufacturer says otherwise; test polished stone because sanded grout can scratch.
- Mix to the stated water ratio, allow the recommended slake time, remix and use within pot life. Extra water weakens grout and promotes efflorescence.
- Force grout diagonally into joints, tool before it sets, and clean haze before it hardens. Do not wash out fresh joints.
- Cure grout per product directions; protect from traffic and water.
- Use flexible sealant, not grout, at movement joints, changes of plane and perimeters.
- Seal only when the product and tile are compatible; some stone and grout need curing first. Repair by removing the defective material, cleaning, matching grout and curing.
Worked example
A polished marble wall has 2 mm joints. The installer plans to use sanded grout because it is stronger. The joint width favours unsanded grout, and the polished surface may scratch under sanded grout. The correct approach is to test a spare piece, use an unsanded or specialty grout compatible with marble, mix to the specified consistency, and avoid excess water. If white salts later appear, the cause is often excessive mixing water or moisture migration; do not simply wash the surface. Allow cure, identify the moisture source and use a cleaner approved for that stone.
Traps
Overwatering grout; cleaning too late; leaving grout in movement joints; sealing damp tile; using acid on acid-sensitive stone; mismatching grout colour; repairing with the wrong grout; failing to cure before traffic.
Key points
- Match grout type to joint width and tile surface.
- Mix grout to the specified water ratio and pot life.
- Tool joints before set and remove haze before it hardens.
- Use flexible sealant at movement joints and changes of plane.
- Repair by removing the defect, cleaning and matching materials.