How many coats of limewash do I need?

A minimum of 3 coats is needed for interior walls, with 4 coats being standard. For exterior walls, 5-6 coats are recommended for durability and weather resistance. Each coat should be thin and watery — thick coats will crack and peel. Apply coats in quick succession (same day if possible) while the previous coat is still slightly damp.

What is the lime putty to water ratio for limewash?

The typical ratio is 1 part lime putty to 1-3 parts water by volume. The first coat should be the thinnest (1:3 ratio) to penetrate the substrate. Subsequent coats can be slightly thicker (1:1.5 to 1:2). The consistency should be like semi-skimmed milk. Too thick and it will crack; too thin and it won't build coverage.

What is casein and why add it to limewash?

Casein is a milk protein that acts as a natural binder, making limewash more durable and water-resistant. Add 20g of casein powder per litre of limewash for exterior use. Dissolve the casein in warm water first to form a paste, then mix into the limewash. Casein makes the limewash slightly more weather-resistant but still allows the wall to breathe — essential for lime buildings.

Can I use limewash on cement render?

No — limewash is only suitable for lime-based surfaces such as lime plaster, lime render, and natural stone. It will not adhere properly to cement render, gypsum plaster, or modern masonry. The lime needs to carbonate (absorb CO2) into the substrate, which only works on compatible lime surfaces. For cement render, use standard masonry paint instead.

How long does limewash last?

Interior limewash lasts 5-10 years before needing a fresh coat. Exterior limewash lasts 3-7 years depending on exposure. South and west-facing walls weather faster. Unlike modern paint, limewash weathers gracefully — it slowly erodes rather than peeling or flaking. Recoating is simple: just dampen the wall and apply 2-3 fresh coats over the existing limewash.

TradeCalculator

Limewash Calculator — Lime Putty, Water & Casein

Calculate limewash quantities for heritage and lime-rendered buildings. Covers 4-6 thin coats with lime putty:water ratios and casein for exteriors.

Wall Area

Total area to limewash

Surface Type

Determines absorption rate

Number of Coats

More coats = better coverage and durability

Price Per kg Lime Putty (optional)

Exterior use (add casein binder)

Casein improves weather resistance

How We Calculate This

This calculator determines limewash quantities for heritage buildings and lime-rendered walls. Limewash requires multiple thin coats rather than thick applications.

The formula

Limewash per coat (L) = Wall area × Coverage rate (L/m²) × Wastage

Total limewash = Litres per coat × Number of coats

Lime putty (kg) = Total litres × 0.5 kg/L

Casein (exterior) = Total litres × 0.02 kg/L

For example, 40 m² exterior lime render with 5 coats at 0.20 L/m²: Per coat = 40 × 0.20 = 8 L. Total = 8 × 5 = 40 L + 15% waste = 46 L. Lime putty = 46 × 0.5 = 23 kg. Casein = 46 × 0.02 = 0.92 kg.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.