Scrim tape or paper tape — which should I use on a joint?

Both tapes exist to stop a crack running along a joint, and they do it in different ways. Scrim relies on its mesh being embedded in the material over it; paper tape relies on being bedded into compound beneath it. Choosing between them is mostly about what is going over the top and how flat the result has to be.

Step by step

1. Decide what the finish will be.A plaster skim over the whole wall, or taping and jointing just the joints. Scrim suits the first; paper tape suits the second.
2. Use scrim where speed and simplicity matter.Self-adhesive, sticks straight onto the board, needs no bedding coat. Patches, small repairs, and joints that are about to be skimmed over in plaster.
3. Use paper tape for a flatter, stronger joint.Paper has more tensile strength across the joint than mesh and finishes flatter, which is why professional taping and jointing uses it. It must be bedded into a coat of compound and squeezed down with a knife.
4. Use paper tape in every internal corner.It is creased down its centre and gives a genuinely straight, crisp angle. Scrim cannot be creased cleanly and tends to telegraph its weave through a thin coat in a corner.
5. Use a corner bead on every external corner.Tape of any kind has no impact resistance. External corners get a metal, plastic or paper-faced bead bedded in and then built out over.
6. Bed paper tape properly or it blisters.Compound under the whole length, tape pressed in, then squeezed down firmly from the middle outwards so no air is trapped. Air behind the tape becomes a blister that has to be cut out later.
7. Embed scrim fully in the coat above it.Scrim left proud shows its weave through the finish. It needs enough material over it to disappear, which is why very thin coats over scrim rarely look right.
8. Build out over either tape in progressively wider coats.Two or three coats, each wider than the last and feathered to nothing. This is what makes the joint invisible, whichever tape is under it.

Tips

• Fibreglass mesh scrim comes in different weights. The heavier ones are better on joints; the very light ones are really only for patching.
• Paper tape is far cheaper than scrim per metre, which matters on a whole room.
• For a wet area, check that the tape and compound you use are suited to it — some jointing compounds are not.
• Never lap two tapes over each other on the same joint. The build-up shows and the doubled layer is harder to feather.

Common mistakes

• Using scrim in an internal corner — Mesh does not fold to a crisp line, so it rounds the angle and the weave often shows through a thin finish coat. Creased paper tape gives the straight, sharp angle that makes a room look properly finished.
• Relying on tape at an external corner — External corners get knocked by furniture, vacuum cleaners and shoulders. Tape has no resistance to impact, so the arris crumbles and the crack follows the corner. A bead is the component that makes an external corner durable.
• Applying scrim over a joint and then skimming with a very thin coat — There is not enough material over the mesh to bury it, so the weave telegraphs through as a visible texture under paint — obvious in raking light and impossible to fix without recoating.

If it doesn't work

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