If your walls are cracked, patchy or uneven, you’ll usually be offered one of two fixes: a skim or a re-plaster. They sound similar, but they’re very different jobs. Here’s what each involves and how to tell which your walls need.
What is skimming?
Skimming is putting a thin finishing coat of plaster, just a few millimetres thick, over a surface that’s already sound. That can be old plaster that’s still firmly attached, or new plasterboard. It’s usually applied in two coats and trowelled smooth, ready to paint once it’s dry.
A skim covers hairline cracks, old filler, dents and rough patches, and the marks left behind when wallpaper or old fittings come off. It’s the quickest way to make a tired room look new.
What is re-plastering?
Re-plastering means taking the old plaster off, back to the brick or block, and starting again. A thicker backing coat goes on first to build the wall back up and get it flat, then a finish coat goes over the top.
It’s a bigger job than a skim. There’s more mess from hacking off the old plaster, it takes longer, and the thicker plaster needs longer to dry before you can decorate.
When a skim is enough
- The existing plaster is firmly stuck to the wall.
- The problems are on the surface: fine cracks, old repairs, dents, rough patches or an uneven finish.
- You’ve stripped wallpaper and the plaster underneath is sound but marked.
- You have new plasterboard that needs a finish.
When you need to re-plaster
- Blown plaster: plaster that has come away from the wall behind it. Skimming over it won’t reattach it, and the new finish can crack or come away with it.
- Crumbling or powdery plaster that breaks up when you touch it.
- Damp-damaged plaster, once the cause of the damp has been found and fixed.
- Large areas of damage, or walls so uneven that a thin skim can’t straighten them.
Small areas of blown plaster don’t always mean the whole wall has to go. They can often be cut out and patched, and then the wall is skimmed.
The tap test for blown plaster
Knock gently on the wall with your knuckles, or tap it lightly with the handle of a screwdriver, working your way across. Sound plaster gives a solid, dull sound. Blown plaster sounds hollow. Mark any hollow areas with a pencil so you can see how big they are. A few small patches usually mean a repair; hollow sounds across most of the wall point to a re-plaster.
Skim or re-plaster at a glance
- Time: skimming an average room is often done in a day or so. A re-plaster takes longer, and needs longer to dry before decorating.
- Mess: skimming is fairly clean. Re-plastering means hacking off the old plaster, which is dusty work.
- Cost: a skim costs less, because there’s less labour and material involved.
- Result: both give a smooth finish, but only a re-plaster fixes what’s wrong behind the surface.
Other options
Dry lining. Instead of re-plastering a very uneven wall, plasterboard can be fixed over it and skimmed. It dries quicker and gives a straight wall, though it takes a little space out of the room. See our dry lining and plasterboarding page.
Lime plaster for older walls. In older houses with solid walls, lime plaster can be a better choice than modern gypsum plaster, because it lets moisture in the walls escape. Where it suits the building, we can talk this through with you.
Not sure which your walls need?
That’s what the quote visit is for. We’ll look at the walls and tell you honestly whether a skim will do or a re-plaster is needed. Four Four Finishes works across Poole, Bournemouth and the rest of Dorset; see our plastering in Dorset page for more. Once the work is done, our guide to how long plaster takes to dry explains when you can decorate.
Frequently asked questions
Can you skim over old plaster?
Yes, as long as it’s firmly attached and in reasonable condition. Any loose or blown areas are cut out and patched first, then the wall is skimmed.
What is blown plaster?
Plaster that has come away from the brick or block behind it. It sounds hollow when tapped and often cracks or bulges. It needs cutting out and replacing rather than skimming over.
Can you skim over painted walls?
Usually, yes, as long as the paint and the plaster underneath are sound. The wall is prepared first so the new plaster bonds properly.
How long does it take to skim a room?
The walls or ceiling of an average room are often skimmed in a day or so. The plaster then needs to dry before painting, often about a week in a warm, ventilated room.
Is re-plastering messy?
More so than skimming, because the old plaster has to be hacked off. We protect floors and furniture while we work and clear up as we go.