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Restore window sills & mullions.
Stone window sill or mullion damage — repaired, re-carved or replaced by a stonemason.
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Costs, timelines, pitfalls and the right questions to ask before any stonemason starts on stone Window Sill & Mullion Restoration.
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Itemised quotes from up to 3 local stonemasons on stone Window Sill & Mullion Restoration — so you can compare like-for-like, not lump sums.
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Top tips
Hiring a stonemason, without the regret.
Four moves that separate a smooth job from a nightmare.
Cement repair
Cement-based repairs visible against weathered stone. Use specialist stone repair mortars (Lithomex, Limestone of Provence colour-matched mixes).
Wrong stone
Indent piece must match quarry source. Generic stones don't match.
Modern tooling visible
Hand-tooling required for heritage match. Machine-cut visibly different.
Drip detail missed
Weather drip on sill underside critical to direct water away. Cheap repairs miss this.
Costs & timeline
Know what it costs. Know when it ends.
Indicative UK ranges and what affects price.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Surface mortar repair (per area)Small areas
£80–£300
Indent repair per indentReplacement piece
£200–£700
Sill replacement (small window)Per sill
£400–£1.2k
Mullion replacementVertical divider
£300–£1.5k
Carved detail repairArchitectural elements
£500–£3.5k
Full window stone restorationSill + mullions + jambs
£800–£4.5k
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
Infographic · VideoThe Stonemason briefing.
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Stonemason quick-view
Video guide
Stonemason explained
Stone window sills and mullions weather and crack over decades. Repair or replacement preserves heritage character. Expect to pay £150–£1,500 per window for UK stone sill or mullion restoration.
What Does the Work Invovle?
Stonemason inspects the damage. Options: surface repair (mortar repair coloured to match stone), indenting (cutting damaged section, inserting new stone), or full replacement (removing and replacing whole sill/mullion). Quarry-matching essential. Hand-tooling to match original surface.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Surface mortar repair (per area) | 80 | 300 | Small areas |
| Indent repair per indent | 200 | 700 | Replacement piece |
| Sill replacement (small window) | 400 | 1,200 | Per sill |
| Mullion replacement | 300 | 1,500 | Vertical divider |
| Carved detail repair | 500 | 3,500 | Architectural elements |
| Full window stone restoration | 800 | 4,500 | Sill + mullions + jambs |
| Scaffolding for elevated work | 200 | 600 | Per window |
How Long Does It Take?
Single repair: 2–4 days. Full window stone restoration: 1–3 weeks. Plus scaffold time.
DIY or Professional?
Professional stonemason only. Architectural stone work requires apprenticed skill.
Choosing the Right Tradesperson
SPAB-accredited heritage stonemason. Listed building experience. Get test repair on small area first.
UK Regulations
Listed buildings need consent. Conservation areas may require specific stone matching. Historic England guidelines.
Common Problems
- Cement repair: Cement-based repairs visible against weathered stone. Use specialist stone repair mortars (Lithomex, Limestone of Provence colour-matched mixes).
- Wrong stone: Indent piece must match quarry source. Generic stones don't match.
- Modern tooling visible: Hand-tooling required for heritage match. Machine-cut visibly different.
- Drip detail missed: Weather drip on sill underside critical to direct water away. Cheap repairs miss this.
Frequently Asked Questions
Replace or repair sill?
Surface damage: repair. Structural cracking or major weathering: replace. Indent for medium damage. Heritage best practice favours repair over replace.
How long does sill last after repair?
Indent repair: 50+ years. Surface mortar repair: 20–40 years (UV and weathering).
Will replacement sill match?
From same quarry as original: very close. Different quarry: visible difference. Many heritage sills are from local quarries no longer active.
Carved sills — costlier?
Yes — hand-carved details (Stretton, gothic) cost 3–5× plain. Worth it for heritage character.
Lime mortar for sill repair?
Yes — for pre-1919 heritage stone. NHL 3.5 typical. Cement-based mortar damages over time.
Architectural detail vs full replacement?
Detail repair: preserves original character, even if patched. Full replacement: cleaner look but loses heritage. Heritage approach favours repair.
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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