The first thing to understand about lime is that it is alive. Not in a romantic sense, but in a precise chemical one: a freshly applied limewash continues to react with the carbon dioxide in the air for weeks after the plasterer leaves, gradually hardening into a surface that is part wall, part atmosphere. Paint dries. Lime becomes.

We use it on almost every project, and we use it differently each time. In Comporta, for Casa Alva, we mixed the lime with sand from the local dunes so the walls have a very slight texture that changes colour as the light rakes across it in the late afternoon. In Lisbon, in the Rua das Flores apartment, the same material was applied more smoothly and tinted with a small amount of yellow ochre pigment, giving the upper walls a warmth that the original plaster had lost under decades of white emulsion.

The colour of a limewashed wall is not fixed. It shifts with humidity, with the angle of the sun, with whether the windows are open or closed. Clients sometimes find this disconcerting at first — they will call to say the wall looks different from how it looked last week, and we have to explain that this is not a defect. It is the whole point. A lime wall is not a backdrop. It participates.

The practical side

There are reasons beyond appearance to use lime. It is breathable in a way that synthetic finishes are not, which matters enormously in old buildings where moisture moves through the fabric of the walls. A building that cannot breathe accumulates damp behind its surfaces. Lime lets moisture in and out without trapping it. In a Pombaline apartment in Lisbon — a building type that has been managing coastal humidity since the eighteenth century — putting a vapour-resistant paint over the original walls is essentially sealing in a problem.

Lime is also, quietly, one of the most sustainable finishes available. It is made by heating limestone — a process that requires energy, but far less than cement — and it reabsorbs carbon dioxide as it cures, offsetting a significant portion of its production emissions over time. It is not zero-impact, but it is honest, and its longevity matters: a well-maintained limewashed surface can last generations. We have worked in houses where the lime on the walls was applied in the 1920s and is still doing its job.

The hardest thing to convey to a client before they have seen it in person is the softness of a lime interior. Photographs flatten it. The quality we are chasing — the way the surface seems to hold light rather than reflect it, the slight irregularity that makes a wall feel like it has been there for a long time — is something you register with your whole body when you walk into a room, not something you can entirely see. That is, perhaps, the best argument for it.