How Much Lime Plaster Do I Need?
Quick Answer
~12–15kg/m² for a two-coat lime plaster system
Based on: scratch coat at 8–10mm + finish coat at 3–5mm, using hydraulic or non-hydraulic lime plaster
How We Calculated This
Lime plaster is typically applied in two or three coats to solid masonry walls:
- Scratch coat (dubbing out): 8–10mm at ~8–10kg/m²
- Finish coat (setting coat): 3–5mm at ~4–5kg/m²
- Total: 12–15kg/m² for a two-coat system
- Example: 7.2m² wall × 14kg/m² = ~100kg of lime plaster
Types of Lime Plaster
- Non-hydraulic lime (fat lime / lime putty): Sets by carbonation (absorbing CO&sub2;), very breathable, ideal for historic buildings. Slower to set — weeks to months.
- Natural hydraulic lime (NHL): Sets by hydration like cement but remains breathable. Available as NHL 2 (slow set), NHL 3.5 (medium), NHL 5 (fast).
- Pre-mixed lime plaster: Ready-to-use products from suppliers like Lime Green, Ty-Mawr, or Mike Wye.
Mix Ratios (if mixing on site)
- Scratch coat: 1 part NHL 3.5 : 2.5 parts sharp sand
- Finish coat: 1 part NHL 2 : 2.5 parts fine sand
- Hair reinforcement: Add goat or horse hair to the scratch coat for crack resistance
When to Use Lime Plaster
Lime plaster is essential for listed buildings and older properties built with lime mortar. It allows moisture to pass through the wall (breathability), preventing trapped damp that gypsum plaster would cause. Building conservation officers typically require lime plaster for any work on Grade I or Grade II listed buildings.
Tips
Keep lime plaster damp for several days after application to allow proper carbonation. Do not use in temperatures below 5°C. Protect from frost for at least two weeks. Lime plaster takes much longer to cure than gypsum — allow 4–6 weeks before applying limewash or breathable paint.