Summary
Lath and plaster (LAP) is the historic UK ceiling and partition wall construction — riven oak or chestnut laths nailed across timber joists / studs, with three coats of lime mortar pushed through the gaps (the "key") and finished on the room face. This system was standard until the mid-20th century. Its repair requires lime-mortar materials, period-appropriate technique, and an understanding of why the original failed.
The single most common LAP repair mistake is treating it like modern plasterboard. Modern materials (gypsum plaster, cement, even modern PVA bonders) are vapour-impermeable; the original LAP is permeable. A modern repair in an old wall creates a vapour barrier that traps moisture against the back of the lime plaster, accelerating the very failure the customer was trying to fix.
This guide covers labour bands by repair scope, lath types and replacement, lime mortar grades and mixes (hair-reinforced), the BS 6915 framework, productivity expectations, and worked pricing examples. For broader plastering work see lime plaster and lime mortar.
Key Facts
- Patch repair, ≤0.5 m² section — £150–£280 labour, 0.5 day
- Small section repair (1–3 m²) — £200–£600 labour
- Whole-ceiling repair (existing laths sound) — £100–£180 per m²
- Whole-ceiling repair (re-lath required) — £250–£450 per m²
- Wall repair (existing laths sound) — £80–£140 per m²
- Wall repair (re-lath required) — £180–£320 per m²
- Period plasterer day rate — £240–£340 regional, £280–£400 London
- Productivity — 4–8 m² per day per operative (slow vs modern plaster)
- Lath strip (riven oak, 1.2m × 25mm × 6mm) — £4–£8 per length
- Lath strip (machine-sawn pine, 1.2m × 32mm × 8mm) — £2–£4 per length
- Galvanised lath nails (4 × 50mm, 1kg) — £8–£15
- Lime putty (25kg tub) — £35–£60
- Hair-reinforced lime (Tradical, Singleton-Birch) — £45–£70 per 25kg
- Sharp sand for lime mortar (25kg) — £6–£12
- Animal hair (yak, goat, ox; specialist supply) — £20–£40 per 1kg
- Lime wash finish coat — £6–£14 per m² applied
- Lime mortar mix ratio (rendering coat) — 1:2.5–1:3 lime:sand + hair
- Lime mortar mix ratio (finish skim) — 1:1.5–1:2 lime:fine sand
- Curing time per coat — 7–14 days
- Total curing for 3-coat system — 4–6 weeks before paint
- Standard ceiling height (Victorian/Edwardian) — 2.7–3.2m
- Standard joist centres (period) — 350–420mm typical
- VAT — 20% standard rate
Quick Reference Table
Spending too long on quotes? squote turns a 2-minute voice recording into a professional quote.
Try squote free →| Scope | Time | Labour | Materials | Full Price |
|---|---|---|---|---|
| Small patch (0.5 m²), existing laths sound | 0.5 day | £120–£200 | £30–£60 | £150–£280 |
| Medium patch (1.5 m²), partial re-lath | 1–1.5 days | £250–£500 | £80–£150 | £350–£700 |
| Whole bedroom ceiling (10–12 m²), existing laths | 1.5–2 days | £350–£600 | £200–£350 | £550–£950 |
| Whole bedroom ceiling, full re-lath | 3–4 days | £700–£1,200 | £400–£700 | £1,150–£1,950 |
| Whole staircase area (15–25 m²) with rosette / cornice | 4–6 days | £1,000–£1,800 | £400–£700 | £1,400–£2,500 |
| Whole property reception room (18–25 m²) | 4–6 days | £1,000–£2,000 | £400–£800 | £1,400–£2,900 |
| Listed building work (premium specialist team) | per m² | £200–£400 per m² | £80–£150 per m² | £350–£600 per m² |
| Wall section repair (3 m² in 2.4m room) | 1 day | £180–£320 | £80–£150 | £280–£500 |
Detailed Guidance
Why Lath and Plaster Fails
Three mechanisms account for 90% of LAP failure:
Key failure — the lime mortar that pushed through the laths has crumbled. Often caused by repeated thermal/moisture cycling or vibration over decades. Plaster falls away from laths in sections.
Lath rot or pull-out — laths nailed too lightly, or oak nails corroded, or laths themselves rotting (often from above due to roof leaks). Plaster sections detach with the laths still attached.
Vapour-trap induced failure — modern repair (cement / gypsum patch) on lime substrate traps moisture; subsequent failure of surrounding original lime plaster accelerates.
The repair must address the cause, not just the symptom. A ceiling repair with a cement patch is not a repair; it's the start of the next failure.
Lath Replacement vs Reuse
Existing laths sound and well-keyed: leave them. New plaster applied direct to original laths is the cheapest and most authentic option. Productivity highest.
Existing laths sound but key compromised: keys are crumbling; new plaster must re-key by being pushed into gaps. New scratch coat with extra hair content.
Laths broken/rotted (sub-section): cut out failed section; splice in new laths; nail to existing joists. New laths typically pine (cheaper, available); for listed buildings, riven oak or chestnut.
Whole ceiling delaminated: full re-lath. Old laths and plaster come off; structural condition of joists assessed; new laths fixed; full three-coat lime plaster.
Inspect carefully. The customer who paid for "a small ceiling repair" doesn't want to discover during the work that the whole ceiling needs re-lath.
Lime Mortar Composition
Traditional lime mortar for LAP is hair-reinforced lime putty plaster:
- Lime putty (non-hydraulic) or NHL2 (very weakly hydraulic) for finish layer
- Sharp sand (well-graded, 0–4mm)
- Animal hair (yak, goat, ox) at 4–6kg per m³ of mortar
- Water as needed for workability
Three-coat system:
- Pricking-up (or rendering) coat — 8–12mm thick, pushed through laths, scored before set
- Floating coat — 6–10mm thick, applied to surface of pricking coat, brought to flat plane
- Skim (or setting) coat — 2–4mm thick, fine lime + finer sand + hair, finished smooth
Each coat must cure before the next. Total system thickness 15–25mm. Curing time per coat 7–14 days; full system 4–6 weeks.
Animal Hair — Why It Matters
Animal hair in lime mortar:
- Reinforces against shrinkage cracks
- Distributes movement across thicker section
- Provides the "spring" that traditional LAP plaster has
Sources:
- Yak hair (Mongolia, China)
- Goat hair (Mediterranean)
- Cow/ox tail hair (UK livestock)
Specialist suppliers: Cornish Lime, Anglia Lime, Singleton Birch. Cost: £20–£40 per kg. Quantity: 4–6 kg per cubic metre of mortar. A typical 12 m² ceiling repair uses ~150 kg of mortar = ~1 kg hair.
Conservation and Listed Buildings
For listed buildings (Grade I, II*, II) and Conservation Areas with Article 4 Directions:
- Listed Building Consent (LBC) required for any material alteration to original fabric
- Conservation Officer typically requires specialist contractor
- Sample panel often required before main works
- Recording of existing condition before any intervention
- Detailed method statement
Add 4–8 weeks to project timeline and £400–£1,200 to conservation officer fees / specialist surveys.
Customer Conversation — The Likely-Expensive Talk
Customers often think LAP repair is a "small job." It rarely is. Explain:
- "Modern plaster on this ceiling fails within 5–10 years, costing more than doing it right."
- "Traditional lime materials and skills are scarce; expect day rates above modern plastering."
- "Curing takes weeks, not days. The room is out of use during cure."
- "For listed buildings, the Local Authority Conservation Officer is involved. This adds time and cost."
Document in writing. Customers later disputing scope or timeline need to see the conversation record.
Surface Decoration After Repair
LAP repair finish takes:
- Lime wash (best — breathable, period-correct)
- Vapour-permeable mineral paint (good — Beeck Mineral Paint, Earthborn Claypaint)
- Standard emulsion paint (acceptable if vapour-permeable; modern emulsion mostly is)
Avoid modern oil-based paints (vapour barrier). Avoid silicone-based coatings on lime substrate.
Common Site Overruns
- Joist condition unknown until ceiling lifted — joist rot or splits discovered; structural repair needed before re-lath
- Wet patch or unknown leak — ceiling failure caused by water from above; repair the leak first
- Asbestos in old artex over LAP — pre-2000 properties; survey before disturbance
- Old hessian-faced plasterboard over LAP — historic "fix"; must be removed and proper re-plaster done
- Underlying laths broken at hidden points — sample inspection misses 50% of failures; ceiling-down survey identifies more
Frequently Asked Questions
Can I just overboard with plasterboard?
You can — and many do — but it's not a repair, it's a cover-up. The underlying LAP continues to fail; eventually the overboard sags or detaches. For non-listed properties where heritage retention isn't a concern, this is sometimes the right pragmatic call. State clearly to the customer: "Overboard hides the issue; doesn't fix it."
How do I find a competent lime plasterer?
Try: the Society for the Protection of Ancient Buildings (SPAB) directory; the Society of Lime Plasterers (UK); the local Conservation Officer's recommended trades list; Limewash and Lime Mortar Federation. Don't rely on standard plastering websites — many list "lime" but lack the actual skill set.
Can lime plaster repair be done in winter?
Indoor work: yes if room temperature kept above 8°C during curing (full system 4–6 weeks). Outdoor work / unheated: no, only March–October. The lime carbonation reaction stops below 5°C; mortars left in cold conditions never reach proper hardness.
Is gypsum bonding-coat ever acceptable on LAP?
Generally no. Gypsum is hydraulic and not vapour-permeable; mixing it with lime substrate creates a moisture-trap zone. For non-listed, non-period properties where a partial modern intervention is accepted, a thin bonding coat may be acceptable for a small specific area — but get specialist advice first.
How long does the repair last?
Properly executed traditional LAP repair: 80–150+ years (the original construction). The system is designed to last centuries with maintenance.
Regulations & Standards
Planning (Listed Buildings and Conservation Areas) Act 1990 — listed building consent regime
Town and Country Planning Act 1990 — Conservation Area protections
National Planning Policy Framework (NPPF) — Chapter 16: heritage
BS EN 459-1:2015 — Building lime — definitions, specifications and conformity criteria
BS 6915:1988 — Specification for design and construction of fully supported lead sheet roof and wall covering (reference for some lead detail interactions)
BS EN 998-1:2016 — Specification for mortar for masonry — rendering and plastering mortar
Historic England: Practical Building Conservation series — authoritative guidance
Historic England: Practical Building Conservation — Mortars, Renders & Plasters
lime plaster — lime plaster technique
lime mortar — lime mortar for masonry
lime mortar repointing pricing guide — companion pricing for repointing
listed building consent — when LBC is required
period property damp — damp diagnosis in period properties