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What is blown plaster and how is it fixed?

Blown plaster is plaster that has come away from the wall behind it, so it sounds hollow, bulges or crumbles. The fix is to find out why it let go, often damp, then cut back the loose area and replaster it.

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What does blown plaster look like?

Plaster is meant to grip the brick, block or board behind it. When that grip fails, the plaster is said to have blown. It may still look fine from a distance, but it is no longer properly fixed to the wall.

Signs to look for:

  • A hollow sound when you tap the wall.
  • A bulge you can see when you hold a torch flat against the surface.
  • Cracks that run round a patch rather than in a straight line.
  • Crumbling or powdery plaster near the floor or around a window.
  • Paint or wallpaper lifting over the same patch.

Blown areas are common on older walls, around windows and chimney breasts, and low down on outside walls. They can also appear where a pipe has leaked inside a wall.

QuoteZila is starting in Cheshire, with Crewe, Nantwich and Sandbach among the first towns, and anyone in the UK can post a job. This page explains blown plaster so you can describe it clearly to a plasterer.

Why does plaster blow?

Plaster lets go for a handful of reasons, and more than one can be at work:

  • Damp. Water in the wall weakens the bond and can carry salts that push the plaster off. GOV.UK guidance describes three main kinds: condensation, penetrating damp that gets in from outside through defects in walls, roofs, windows or floors, and rising damp from the ground [S1].
  • Age. Older plaster can simply lose its key to the wall after many decades.
  • A leak. A dripping pipe or a failed seal round a bath or shower can soak the wall behind the plaster.
  • Poor preparation. Plaster laid on a dusty, very dry or very smooth background may never have bonded well.
  • Movement or knocks. Vibration, settling and heavy impacts can loosen a weak patch.

The cause matters more than the patch. New plaster on a wall that is still wet will often blow again.

When is a patch enough?

A small, dry hollow area with a clear cause, such as an old leak that has been fixed, can usually be cut back and patched. The plasterer removes the loose plaster back to firm edges, prepares the background and builds the area back up to match the wall around it.

A full replaster of the wall makes more sense when:

  • Hollow patches are spread across most of the wall.
  • The plaster is soft or powdery as well as loose.
  • Damp has affected a large area and the wall needs a different plaster to cope with it.
  • You are already decorating and want one flat finish.

On an outside wall, a big area matters for another reason. The Planning Portal says that where 25 per cent or more of an external wall is re-plastered or re-lined internally, building regulations would normally apply and the insulation would normally have to be improved [S3]. Ask the plasterer about this if they suggest stripping a whole outside wall.

What about dust and old coatings?

Hacking off plaster is messy work. HSE says regularly breathing construction dust can cause diseases including asthma and silicosis [S4]. Clear the room, seal doorways and keep children and pets away while the work is done.

Old finishes need more care. HSE says asbestos can be found in any home built or refurbished before 2000, and lists textured decorative coatings such as Artex among the places it can be found inside a house [S2]. If the blown area has a textured finish, or a board behind it you are unsure about, ask for it to be tested before it is broken out. You can read HSE's diagrams of where asbestos can occur.

What should you ask a plasterer?

Ask each plasterer the same questions:

  • What do you think caused it, and does that need fixing first?
  • How far back will you cut, and what will you patch with?
  • Will the patch match the plaster around it, or should the whole wall be done?
  • How long must it dry before it can be painted?
  • Who clears the rubble, and is that in the price?

If the plasterer thinks damp is the cause, you may also want a damp specialist to look at the wall. Citizens Advice suggests getting written quotes from at least three traders, and says a quote is a fixed price while an estimate is a rough guess [S5].

Jobs you might post

These are examples, not taken from real job posts.

  • "Hollow, bulging plaster under the living room window, roughly a metre wide. Please quote to cut out and patch."
  • "Plaster crumbling along the bottom of an outside wall in an older terrace. Looking for advice on the cause and a quote to replaster."
  • "Old leak behind the bath has been fixed. The plaster on the wall next to it has blown and needs redoing."

Get quotes for blown plaster

Describe the wall, the size of the hollow area, any damp you have seen and what is on the wall now, with photos if you can. Up to five matched local businesses can send you a quote [QZ2]. QuoteZila is free for customers and local businesses [QZ1].

Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.

Posting a job is not open yet

See our plasterers page and damp proofing page. For cracks rather than hollow patches, see cracked plaster. For pricing, see what changes the cost of a plasterer.

Questions about blown plaster

How do I know if plaster is blown?

Tap the wall gently with your knuckles or the handle of a screwdriver. Sound plaster gives a dull, solid knock. Blown plaster sounds hollow or drummy, and it may bulge, crack in a rough circle or crumble when pressed. Mark the edges in pencil so a plasterer can see the area.

Can blown plaster be left alone?

A small, dry hollow patch that is not spreading can sometimes wait. Plaster that is bulging, falling or damp should be looked at, because it can drop off the wall and the cause behind it may keep spreading.

Does blown plaster mean I have damp?

Not always, but damp is a common reason. GOV.UK guidance describes condensation, penetrating damp from defects in walls or roofs, and rising damp from the ground, and says rising damp is often misdiagnosed. Find the cause before you pay for new plaster.

Is it safe to knock off old plaster myself?

Be careful. HSE says asbestos can be found in any home built or refurbished before 2000, including textured coatings such as Artex. Plaster dust is also harmful to breathe. If a wall has an old textured finish, have it checked before anyone breaks it out.

Does QuoteZila check the plasterers who quote?

No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.

This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.

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Sources

  1. QZ1: QuoteZila product fact. QuoteZila home and FAQ copy.
  2. QZ2: QuoteZila product fact. QuoteZila FAQ How does getting quotes work.
  3. S1: Understanding and addressing the health risks of damp and mould in the home, GOV.UK (DHSC and MHCLG). Accessed 2026-11-01. https://www.gov.uk/government/publications/damp-and-mould-understanding-and-addressing-the-health-risks-for-rented-housing-providers/understanding-and-addressing-the-health-risks-of-damp-and-mould-in-the-home--2
  4. S2: Diagrams showing where asbestos can occur in buildings, HSE. Accessed 2026-11-01. https://www.hse.gov.uk/asbestos/diagrams.htm
  5. S3: External walls: building regulations, Planning Portal. Accessed 2026-11-01. https://www.planningportal.co.uk/permission/common-projects/external-walls/building-regulations/
  6. S4: Construction dust, HSE. Accessed 2026-11-01. https://www.hse.gov.uk/construction/healthrisks/hazardous-substances/construction-dust.htm
  7. S5: Before you get work done on your home, Citizens Advice. Accessed 2026-11-01. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/