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Treat penetrating damp.
External cause diagnosed (pointing, render, gutter or chimney) and fixed — then internal repair if needed.
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Source not identified
Spending £000s on internal plaster without fixing source. Damp returns within months.
Cement render on solid walls
Cement render on pre-1919 brick traps moisture, accelerates damp. Use lime render.
Cavity wall ties bridged
Old mortar droppings in cavity bridge across, drawing moisture. Specialist removal needed.
Cracked pointing not visible
Hairline cracks let water in. Detailed external inspection essential.
Costs & timeline
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Indicative UK ranges and what affects price.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Damp survey + cause identificationPCA-qualified
£120–£400
Repointing per m²Solid wall, lime mortar
£30–£80/m²
Render repair per m²Cement or lime
£40–£90/m²
Gutter clean/repairMost common source
£80–£400
Roof tile or flashing repairOften the source
£200–£800
Internal plaster replacementPer m², salt-resistant
£50–£120/m²
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
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Penetrating damp enters through walls from outside — usually via failed pointing, render, gutters or flashings. Expect to pay £400–£3,500 for UK penetrating damp diagnosis and treatment, depending on the cause and area affected.
What Does the Work Involve?
Surveyor identifies water entry point — usually the upper edge of the visible internal damp patch. Common sources: failed pointing on solid walls, cracked render, broken or blocked gutters, missing roof tiles, failed lead flashings, cracked chimney pots, defective windowsill, debris in cavity. Fix at source (often roofer or builder work, not damp specialist). Internal: allow walls to dry, then strip salt-contaminated plaster, re-plaster with salt-resistant render.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Damp survey + cause identification | 120 | 400 | PCA-qualified |
| Repointing per m² | 30 | 80 | Solid wall, lime mortar |
| Render repair per m² | 40 | 90 | Cement or lime |
| Gutter clean/repair | 80 | 400 | Most common source |
| Roof tile or flashing repair | 200 | 800 | Often the source |
| Internal plaster replacement | 50 | 120 | Per m², salt-resistant |
| Cavity wall debris removal | 400 | 1,500 | If cavity bridged |
| Whole-wall fix (typical) | 800 | 3,500 | External + internal |
How Long Does It Take?
Source repair (gutter, tile, pointing): 1–2 days. Internal drying time: 4–8 weeks. Re-plastering: 1–2 days. Re-decoration: after drying.
DIY or Professional?
PCA-qualified diagnosis recommended. Source repair varies — gutter is plumber; roof is roofer; pointing is bricklayer. Internal plaster needs experienced plasterer.
Choosing the Right Tradesperson
PCA-qualified surveyor for diagnosis. Different specialists for each potential fix. Co-ordinated approach — surveyor lists faults; specialists fix; replasterer follows.
UK Regulations
No specific Building Regs unless major work. Listed buildings need consent for repointing or render work.
Common Problems
- Source not identified: Spending £000s on internal plaster without fixing source. Damp returns within months.
- Cement render on solid walls: Cement render on pre-1919 brick traps moisture, accelerates damp. Use lime render.
- Cavity wall ties bridged: Old mortar droppings in cavity bridge across, drawing moisture. Specialist removal needed.
- Cracked pointing not visible: Hairline cracks let water in. Detailed external inspection essential.
Frequently Asked Questions
How do I find the source of penetrating damp?
Look ABOVE the internal damp patch on the outside — water enters at one point and tracks down inside. Visible defects: cracks, failed pointing, missing tiles, blocked gutters.
Will internal treatment alone fix penetrating damp?
No — the source must be fixed externally. Internal treatment without source fix is pointless.
Cement or lime render on a Victorian house?
Lime mortar on solid-wall (pre-1919) properties. Cement render traps moisture and accelerates damp. Lime breathes.
How long until I can decorate?
Allow walls to dry fully after source fix — typically 4–8 weeks. New plaster needs further 2–3 weeks drying. Total 6–11 weeks before paint.
Will rendering my house fix damp?
Properly specified render (breathable lime on old buildings, weather-shield on modern) can. But always address pointing, gutters, roof first — they're usually the actual source.
Cavity wall — bridge debris?
Common in 1930s–1970s homes. Mortar droppings during construction settled in cavity, bridging across. Specialist cleaning £400–£1,500.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
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