Lime plaster, and what it does to a north-facing roomLime plaster, and what it does to a north-facing room

What the light actually does

North light never moves. It arrives flat and stays flat, and because it carries no warmth it reads every surface as slightly colder than it is. Paint answers that badly — a flat emulsion in a north room goes chalky by mid-afternoon and dead by four, and the usual fix of warming the colour a step or two only makes the wall look like it is apologising.

Lime plaster answers it differently. The finish is not one plane but a shallow depth of overlapping trowel passes, so the wall holds a little shadow of its own. In flat light that shadow is the only thing giving the surface any variation, and it turns out to be enough. The room stops reading as cold and starts reading as quiet.

Three coats, and no sealer

We specify three coats over a lime-compatible base: a scratch coat to key, a levelling coat, and a thin finish coat burnished while it is still green. The burnishing is what closes the surface. It is also the step most often lost when a programme slips, and losing it is why some lime walls dust.

We do not seal it. A sealed lime wall is a painted wall with extra steps — it stops breathing, stops adjusting to humidity, and gives up the chalky depth that made anyone want it in the first place. In a bathroom we will accept a soap finish on the splash zone and nothing else.

Paint sits on a wall. Lime plaster becomes one — which is why it takes a fortnight, and a plasterer willing to say no to you.

What it costs, honestly

Reckon on three to four times a good painted finish, and almost all of that is labour. The material is cheap; the fortnight of a plasterer who has done it two hundred times is not. We price it room by room rather than house-wide, because it is worth spending on the two rooms with the worst light and not worth spending on a hallway nobody stands still in.

That room-by-room habit also gives you an exit. If the budget moves in the wrong direction halfway through, dropping lime from the back of the house is one conversation, not a redesign.

Where we do not use it

Not behind a hob. Not in a utility room. Not on a wall that a family with young children will run their hands along daily for ten years, unless everyone has agreed in advance that the marks are the point. Lime records what happens to it, which is the entire argument for it and the entire argument against.