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How to tape internal corner plasterboard joints with joint tape

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Internal corner plasterboard joints Joint tape can also be used to seal corner joints where two sections of plasterboard meet.

As well as vertical corner joints, horizontal internal corners occur in between the ceiling and the wall beneath it.

Paper jointing tape Because it can be creased crisply along its length, paper tape is most suitable for this task.
Inside corner trowel As for other types of plasterboard joint, taping internal corner joints requires a set of taping knives. However, there is an additional tool called a corner trowel (sometimes known as a corner knife) which is particularly useful.

Its bent blade allows the user to effectively guide the creased tape deep into the internal corner joint when they run it along the tape’s length. It also means that both sides of the joint can be worked on at the same time.

Applying base coat of jointing compound to internal corner joint

Step 1 – Apply base coat of compound

To begin, apply jointing compound to both sides of the joint, using your 150mm taping knife.

Try to cover the joint evenly without creating bumps as this will make it easier to flatten the tape into position later on.

Folding paper jointing tape along its length

Step 2 – Crease tape

Cut your tape to length, then run your fingers along its crease to fold it in half.

Fixing jointing tape into internal corner by hand

Step 3 – Secure tape to wall

Position your tape at one end of the joint with the outside crease against the inside corner.

With your fingers, press the tape into place so that it is held onto the wall.

Drawing taping knife along length of jointing tape

Step 4 – Guide tape into corner

Use your corner trowel or your smallest taping knife to guide the outside crease of the paper deep into the corner.

Then, starting at one end, draw your knife or trowel along the length of the tape on either side of the fold to fix it into position.

Wonkee Donkee says: 'Dipping your taping knife or corner trowel in water will help it to glide along the tape and prevent the tape from moving out of place.'
Applying jointing compound to corner joint with trowel

Step 5 – Cover tape with compound

Once the fold of the tape is sitting tightly against the corner of the joint, it is time to embed it in jointing compound.

Load your 150mm taping knife or corner trowel with jointing compound and apply it evenly to both sides of the joint, covering the entirety of the tape.

Feathering edges of jointing compound with 6 inch taping knife Using a corner trowel is likely to leave ridges on either edge of the joint as excess compound is pressed out from underneath the tool.

To get of these ridges, use a small taping knife to scrape off the excess compound and feather the edge of the joint.

Wet sanding plasterboard joint

Step 6 – Sand

Allow the second layer of jointing compound to dry and then blend the edges of the joint into the surface of the plasterboard using a damp sponge or sanding block.

This will create a smooth surface upon which the third coat of compound can be applied.

Applying third coat of compound to corner joint

Step 7 – Apply third coat of compound

Building upon the second layer, with your 200mm taping knife, apply a third and final coat of compound, widening the area covered on either side of the corner joint.

Smooth the compound, feathering the edges by applying pressure to only one side of your taping knife.

Taped and jointed internal corner joints and tapered horizontal joints

Step 8 – Leave to dry then sand

Once the third coat of jointing compound has dried, repeat the sanding process to remove any imperfections.

When the corner joint has been blended into the plasterboard on either side, it is ready to be primed and painted.