Blown plaster describes plaster that has lost adhesion to the wall or ceiling behind it. It is very common in older properties, particularly Victorian and Edwardian homes, where the original lime plaster has failed over decades of movement and damp.
How to Test for Blown Plaster
Knock the wall firmly with your knuckles. Solid, well-adhered plaster produces a dense, heavy sound. Blown plaster sounds hollow — a dull, drum-like resonance that is immediately recognisable once you know what to listen for. You may also feel the plaster flex slightly under light pressure.
What Causes Plaster to Blow?
- Damp penetration — the most common cause; water gets behind the plaster and breaks the bond
- Structural movement — slight settlement or vibration over decades
- Rust from embedded metalwork — old iron wall ties or embedded metal expands as it rusts, pushing plaster off
- Failed plaster keys — in old lime-and-hair plaster on timber lath, the keys (plaster pushed through the gaps) fail over time
Blown Plaster Repair Costs
| Scale of work | Typical cost |
|---|---|
| Small patch (up to 1m²) | £100–£200 |
| Medium patch (1–4m²) | £200–£500 |
| Half a room | £400–£800 |
| Full room replaster | £600–£1,200 |
Can Blown Plaster Be Patched?
Isolated patches can be hacked off and replastered. The challenge is matching the texture and level of surrounding plaster. In rooms where only isolated areas are blown, patching is perfectly acceptable. Where large areas are affected, a full re-plaster of the wall or room is usually better value in the long run.
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