Drywall Finishing, Taping, and Joint Treatment
Finishing is where the trade is judged. This domain tests levels of finish, compound selection, coat sequencing, corner treatment, and diagnosis of visible defects.
Levels of finish
- Level 1: joints taped and set only, for plenums and above ceilings.
- Level 2: tape plus one coat, for garages, warehouses and behind tile on water-resistant board.
- Level 3: tape plus two coats, for surfaces receiving medium or heavy texture.
- Level 4: tape plus three coats, feathered and sanded, the default for flat paint in most residential and commercial work.
- Level 5: Level 4 plus a full skim coat, required for gloss and semi-gloss paint and for critical side-lighting or wall-wash lighting.
Sequence
Prefill gaps and set corner bead, then a taping coat with a 100-125 mm knife, a fill coat at 150-200 mm and a finish coat at 250-300 mm, letting each coat dry and scraping ridges before the next. Feather each joint to roughly twice its width. Sand with 120-150 grit, check under a grazing light, dust off and prime.
Use setting compound for prefill and first coats, and lightweight topping for final coats. Do not sand through the paper face, and do not leave dust on the wall before priming.
Worked example
A Level 4 wall painted with semi-gloss shows every joint as a shadow when a downlight washes the wall.
Reasoning: this is telegraphing, caused by joints feathered too narrowly and by a level of finish too low for gloss paint under critical lighting. More paint will not fix it. Rake the joints wider, sand flat and check with a straightedge, then skim the whole surface to Level 5 before repainting. On the estimate, the specification should have called Level 5 for that lighting condition.
Traps
Taping with topping compound; recoating before the previous coat is dry; over-sanding into the paper; leaving a hard knife ridge; mesh tape in a fire-rated joint; skipping primer, which then shows as uneven sheen.