Skim over the old plaster, or take it off?

Test it before you decide

Tap the wall across its whole area, including low down near the skirting and high up in the corners. A dull note means the plaster is still bonded to the wall behind it. A hollow note means it has let go, and everything you put on top of it is only as good as that failed bond.

Also look for: cracking that runs in a pattern rather than a single line, plaster that moves slightly under hand pressure, powdery or sandy material coming away at the edges, and any damp staining.

When skimming over is right

The existing plaster is solid, the surface is just tired, uneven, or covered in old textured coating that is well stuck. In that case a skim coat over the top gives you a new, flat surface at roughly half the cost and half the disruption of taking it back. There is no compromise in the result — the finish is the same finish.

When it has to come off

It sounds hollow over any meaningful area. It is damp, or has been. It is blown around a chimney breast, which is common where old fires have left salts in the wall. Or it is so uneven that a skim coat could not flatten it without being unrealistically thick.

Taking it off is dirtier, louder and more expensive, and it is the only thing that works in those situations. A skim over blown plaster fails as a single sheet, usually taking a bit of your decoration with it.

The cost difference

As a rough guide, stripping back to brick and re-plastering a room runs to roughly half as much again as skimming over, sometimes more if there is a lot of waste to remove. The gap is preparation and disposal, not skill or materials.

What we will tell you

We will tap the walls at the visit and tell you which category you are in, and why, before quoting. If half the room can be skimmed over and one wall has to come off, that is what the quote will say — it is a common answer and it is cheaper than doing the whole room the hard way.

Questions we get asked about this