What is limewash? The traditional lime wall coating, how it works, and which homes it suits

What is limewash, and what does it have to do with lime?

Lime is something Thai people already know well, from building work and from farming, where it's used to treat acidic soil. Limewash is simply that same lime mixed with water until thin, with pigment added, then brushed onto a wall in several thin coats.

This method has been used for hundreds of years in many parts of the world, from country houses in Europe and seaside homes on the Mediterranean to old buildings in Asia. The reason is simple: lime is easy to find, inexpensive, and the same material as the lime plaster already on the walls, so wall and paint become one.

The lime cycle: from limestone back to limestone

What makes limewash special is the chemistry behind it. It doesn't dry like ordinary paint, where the water evaporates and leaves a film on the surface. It hardens by turning back into stone. Building conservators call this process the lime cycle.

• It starts with limestone, which is calcium carbonate
• This is burned at high temperature to make quicklime, or calcium oxide
• Adding water makes slaked lime, or calcium hydroxide; this stage produces intense heat and is dangerous
• The lime is mixed with water and pigment to make limewash, which is brushed onto the wall
• On the wall, the lime slowly absorbs carbon dioxide from the air and hardens back into calcium carbonate, just like the limestone it started as

What a limewashed wall looks like: matt, soft and never still

A limewashed wall has a chalky matt surface. Its colour isn't even across the whole wall but clouded lighter and darker, following the brush marks and the thickness of each coat. The same wall looks different in the morning and the evening, because its uneven surface catches the light differently as the sun moves.

Something else that surprises first-timers is that limewash is much darker wet than dry. Wait until it's dry before deciding whether the colour is right. And because lime is highly alkaline, the pigments that can be used are usually mineral ones, so the tones come out soft, like earth, sand and stone, rather than bright. Like a cotton shirt washed many times, the more it fades, the better it looks.

The pros and cons of limewash to know before you paint

Limewash isn't better than house paint at everything. It's very good at some things and clearly weak at others. Know both sides first so you won't be disappointed.

• Pro: it lets moisture escape very well and doesn't trap water in the wall, so it suits old plaster and brick walls
• Pro: its alkalinity makes it harder for mould to grow on the surface
• Pro: it gains charm with age, and touch-ups blend easily with the original
• Con: the surface is chalky, so rubbing hard can mark hands or clothes, and it can't be scrubbed like acrylic paint
• Con: exterior walls exposed to heavy rain wear and fade faster and need recoating from time to time
• Con: it only bonds well to absorbent mineral surfaces; it can't go directly over existing acrylic paint, glossy surfaces, wood or metal
• Con: wet lime burns skin and is dangerous to the eyes; always wear gloves and safety glasses
• Con: each batch may not match exactly, so it needs several thin coats and a fair amount of skill

Which walls can take limewash, and which shouldn't

Before you fall in love with pictures of beautiful walls, look at your own. Limewash needs an absorbent wall. If you drip water on it and the wall soaks it up, there's a chance. If the water beads and runs down, there's a paint film or coating, and the surface needs preparing first.

• Suitable: bare plaster that has never been painted, lime plaster, brick, stone, and old buildings that used lime from the start
• Needs special preparation: walls already painted with acrylic, plasterboard
• Not suitable: wood, metal, glossy surfaces, areas that are always splashed with water, and walls that get touched a lot, such as hallways in homes with young children

How real limewash differs from limewash-style paint

These days the word limewash is used much more broadly, often meaning the look rather than the material. The main difference is the binder. Real limewash uses lime that hardens through the lime cycle. Limewash-style paints use other binders to get a similar look, in exchange for going more easily onto primed walls, more even colour, and no handling of wet lime.

Voqe Mineral Finish is in the second group: a matt, limewash-style mineral paint applied in two tones in alternating directions to create depth, on primed plaster walls, inside and out. If your home is an old building plastered in lime and you want to keep its walls breathing as they always have, real limewash is the answer. If it's an ordinary plastered house and you want this look with easy upkeep, a limewash-style paint is the better fit.