How do I tape and joint plasterboard properly?

Taping and jointing finishes only the joints and the fixings rather than the whole surface. It is slower than skimming in elapsed time and far easier for a non-plasterer, because every stage is forgiving and correctable.

What you'll need

• Tapered-edge plasterboard
• Paper joint tape and corner tape
• Jointing compound — setting or ready-mixed
• A 150mm, 250mm and 300mm taping knife
• A mud pan or hawk
• A sanding sponge and a pole sander
• A dust mask

Step by step

1. Plan the boarding for it.Taping and jointing needs tapered-edge boards, arranged so the tapered edges meet. Cut edges have no taper and produce a much harder joint to hide.
2. Get the fixings right.Screws dimpled just below the paper, at 200–300mm centres, none within 10mm of a board edge. A proud screw ruins a joint you cannot then flatten.
3. Fill the recess first.Where two tapered edges meet there is a shallow trough. Fill it with compound and let it set before taping, so the tape sits in a filled joint rather than bridging a gap.
4. Bed the tape.A layer of compound along the joint, tape pressed into it, then draw a 150mm knife along to squeeze the excess out — leaving a thin layer behind the tape, not none.
5. Do the corners with creased tape.Paper tape has a centre crease for internal corners. Bed one side, then the other, and clean the angle with a corner knife or the edge of a taping knife.
6. Use metal or paper-faced bead on external corners.External angles take knocks and need a bead. Bed it in compound, or fix mechanically, and build the compound out over it in coats.
7. Apply the second coat wider.Once the tape coat is dry, a 250mm knife over the joint, feathering the edges. This is where the joint starts to disappear.
8. Apply the third coat wider again.A 300mm knife, very thin, feathered right out. Three coats of increasing width is the whole method.
9. Coat the screw dimples as you go.Each of the three passes, a knife over the line of screws. They need the same treatment as the joints.
10. Let everything dry between coats.Setting compounds go off chemically and can be recoated by the clock. Ready-mixed dries by evaporation and needs real time, longer in a cold or humid room.
11. Sand at the end only.A sanding sponge or a pole sander with fine mesh. The aim is to knock off ridges, not to flatten the joint — that should already be flat.
12. Check with a torch.Held flat against the wall, sweeping along the joint. It shows every ridge and hollow. Correct with a thin coat rather than more sanding.
13. Prime the whole surface.Compound and board paper have very different absorbency. A drywall primer or a full mist coat is essential or every joint will show through the paint.

Tips

• Setting compounds are named by their working time — 45 minute, 90 minute and so on. A slower one gives you time to work; a faster one lets you get two coats on in a day.
• Keep the compound clean. A single lump of dried material on the knife drags a groove down the whole joint and has to be filled again.
• Wet sanding with a damp sponge produces almost no dust and is far kinder in an occupied house, though it is slower.

Common mistakes

• Trying to build the joint up in one thick coat — Thick compound shrinks and cracks, and a narrow band of thickness is a permanent ridge. The method depends on thin coats getting progressively wider — that is what turns a 3mm build-up into an invisible slope.
• Sanding to fix a bad joint — Sanding removes material from the high points, which are the edges of your feathering, and eventually cuts through to the tape. A hollow or a ridge is corrected with another thin, wider coat, not with abrasive.

If it doesn't work

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