Making Lime Wash — The Oldest and Simplest Wall Paint in the World

Start with 1 kg of slaked lime (calcium hydroxide, Ca(OH)₂). Slaked lime is available as a dry powder (hydrated lime) or as a wet putty (lime putty, which has been soaked for weeks or months and is smoother). Lime putty gives a finer finish than dry powder. If using dry hydrated lime, mix it with enough water to form a thick paste and let it stand overnight — this 'slaking' period improves the workability. WARNING: slaked lime is strongly alkaline (pH 12-13). Wear gloves and eye protection. Avoid skin contact and do not inhale the dry powder.

Gradually add water to the lime putty or hydrated lime paste, stirring continuously, until the mixture reaches the consistency of full-cream milk — thin enough to brush easily but not watery. For 1 kg of slaked lime, this typically requires 3-5 litres of water. Stir thoroughly and strain through a fine mesh to remove any lumps or undissolved particles. Lumps will cause streaks and an uneven finish. The mixture should be smooth and uniform.

For a tinted lime wash, add earth pigment powder to the mixture: yellow ochre for a warm cream, red ochre for a terracotta pink, raw umber for a warm grey, lampblack for a cool grey. The pigment should not exceed 10% of the lime weight — too much pigment weakens the binding. Mix the pigment with a little water to form a smooth paste before adding to the lime wash, to avoid lumps. Note that lime wash always dries lighter than it appears when wet — test a sample patch and let it dry before committing to the colour.

Dampen the wall surface with clean water before applying lime wash — dry surfaces absorb the water too quickly, preventing proper carbonation. Apply the lime wash in thin, even coats using a wide, soft-bristled brush (traditionally a large flat masonry brush or a thick round brush called a 'limewash brush'). Work quickly and do not over-brush. Each coat should be very thin — translucent when wet. Let each coat dry for 24 hours before applying the next. Apply 3-5 thin coats for a full, luminous finish. The coating will appear patchy when wet but dries even.

After the final coat, the lime wash needs time to carbonate — the calcium hydroxide absorbs CO₂ from the air and converts to calcium carbonate, forming a hard, crystalline surface. This process takes 1-4 weeks depending on humidity and temperature. Do not paint in direct hot sunlight or frost — moderate temperatures (10-25°C) and some humidity give the best carbonation. The finished surface is a luminous, chalky matte white (or tinted colour) with a subtle depth and texture that deepens with each new coat over the years. Lime wash can be recoated annually — each layer adds to the accumulated surface.