Can You Skim Over Old Plaster? Re-Skimming Guide

Yes — you can skim over old plaster, but only if the existing plaster is sound, well-bonded, clean and properly prepared. If the old plaster is blown (hollow), soft, cracked, or lifting from the wall, skimming over it is a waste of money: the new skim will move with the failed base and crack or come away. The decision to re-skim or to remove and re-plaster depends entirely on the condition of what's underneath.

When you can skim over old plaster

Re-skimming is suitable when the existing plaster is:

• Solid — no hollow or drumming areas when tapped
• Well-bonded — firmly attached to the wall
• Clean — free of dust, grease, wallpaper paste and flaking paint
• Reasonably flat — a skim is thin (1–3 mm); it can't straighten a badly wavy wall
• Stable — no widespread cracking or damp

If those conditions are met, a re-skim gives a fresh, smooth surface without the cost and mess of removing the old plaster.

When you should not skim over old plaster

Remove and re-plaster instead when:

• The old plaster is blown (hollow when tapped) — it has parted from the wall
• The surface is soft or crumbling — it won't support a new coat
• There's widespread cracking or the plaster is moving
• The wall is damp — the cause must be fixed and the damaged plaster removed
• The wall is very uneven — a skim can't fix deep undulations; a backing coat can

Skimming over a blown or damp background is the most common reason a re-skim fails. The new coat looks fine for a few weeks, then cracks or hollows as the weak base gives way.

How to tell if old plaster is sound

Tap the wall with your knuckle or a small hammer:

• Solid, dull thud — the plaster is bonded; re-skimming is likely fine
• Hollow, drumming sound — the plaster has parted from the wall (blown); it needs removing

Blown areas feel different — the sound changes across a wall, so tap a few spots. Any hollow patches mean that section at least needs to come off.

Preparing old plaster for a re-skim

1. Remove wallpaper and paste residue — completely
2. Clean the surface — sugar soap or similar to remove grease and grime
3. Cut out any cracks — open them slightly so they can be filled and reinforced
4. Remove or pin any blown patches — don't skim over hollow areas
5. Key the surface — a bonding agent or a scratch where the surface is very smooth
6. Prime — with the right bonding agent for the background, following the manufacturer's guidance

Re-skimming vs full re-plaster

| | Re-skim | Full re-plaster | |---|---|---| | What's there | Sound old plaster | Blown/damaged plaster | | Process | Prep + skim | Remove + backing coat + skim | | Cost | Lower | Higher | | Mess | Less | More | | When to choose | Old plaster is solid | Old plaster is blown or damp |

See our replastering costs page for what full re-plastering involves.

Skim thickness over old plaster

The skim still goes on thin — 1–3 mm. A thicker skim to "fill" an uneven old wall is the wrong approach; it shrinks, dries slowly, and cracks. If the wall needs truing up, that's a backing coat, not more skim. See our skim thickness guide.

Related: skimming walls and ceilings

The technique for re-skimming is the same as skimming any surface. Our skimming walls guide covers the process, and our wall skimming London service handles the work.

FAQ

Can you skim over old plaster? Yes, if the old plaster is sound, solid, clean and well-bonded. If it's blown, soft or damp, it should be removed first.

How do I know if my old plaster is sound? Tap it. A solid, dull thud means it's bonded; a hollow, drumming sound means it's blown and needs removing.

Can you skim over cracked plaster? Fine cracks can be cut out, filled and reinforced before skimming. Widespread or structural cracking needs the cause addressed first.

Is re-skimming cheaper than re-plastering? Yes — re-skimming is a thin coat over a sound surface, so it's less labour and mess than removing old plaster and applying a backing coat.

How thick is a re-skim over old plaster? 1–3 mm, the same as any skim. A skim isn't for building up or straightening a wall — that needs a backing coat.

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Not sure whether your walls need a re-skim or a full re-plaster? Send London Plastering Service a few photos and tap-test results, and we'll advise on the right approach, with a free quote.