Systems & Finishes - Breathable
Lime & breathable systems.
For solid walls, listed interiors and anywhere a modern coating would trap what the building needs to let out. The oldest answer to damp and still the correct one.
A solid brick or stone wall built before about 1919 has no cavity and no damp-proof course and it was never meant to. It handles water by absorbing it in wet weather and releasing it again in dry, through a lime plaster and a lime or distemper finish that let vapour pass. It works and it worked for centuries.
What breaks it is a modern coating. Cement render, gypsum skim, plastic-emulsion paint and waterproof membranes all resist vapour, so the moisture that gets in cannot get out. It goes sideways and upwards instead and reappears as rising damp, blown plaster, salt bloom and rotting joinery - usually blamed on the wall rather than on the coating that was added to it.
What we install
- Lime plaster. Hydraulic or putty lime, on the hair, in traditional coats where the substrate calls for it.
- Lime render. Externally, on solid walls where cement render has failed or is causing failure.
- Limewash and mineral paint. The finish has to breathe too, or the plaster underneath cannot do its job.
- Insulating lime systems. Where thermal improvement is wanted without turning a breathable wall into a sealed one.
Why lime moves with the building
Lime is softer than the masonry it sits on and it is meant to be. When an old wall moves - and it does, seasonally - a lime plaster accommodates it in hairline crazing distributed across the surface, which then partly self-heals as free lime carbonates in the crack. Cement is harder than the brick, so it does not move; the brick face spalls instead. That is the whole argument for lime on a period building and it is a structural argument rather than an aesthetic one.
What it asks of a programme
Patience. Lime cures by carbonation with atmospheric carbon dioxide, not by hydration and that takes weeks rather than days. Coats have to be left. It cannot be forced with heat and it cannot be applied in frost. If a programme has no room for that, lime is the wrong specification and we would rather tell you at drawing stage than be blamed for a wall that failed because it was rushed.
Listed and conservation work
On a listed building the specification is frequently not a matter of preference - a breathable system is what consent requires. We are comfortable working to a conservation officer's or a heritage consultant's specification and we would rather see it early than price against an assumption.
On site
Lime plaster, as installed.
Questions we get asked.
Why use lime plaster instead of gypsum on an old wall?
Because a solid wall built before about 1919 has no cavity and no damp-proof course and it manages water by absorbing and releasing it. Gypsum skim, cement render and plastic emulsion all resist vapour, so moisture that gets in cannot get out and reappears as rising damp, blown plaster and salt bloom. Lime lets the wall do what it was built to do.
Will lime plaster fix damp?
It removes one very common cause of it, which is a non-breathable coating trapping moisture in a solid wall. It will not fix a leaking gutter, a raised external ground level, a failed roof or a bridged cavity. If a wall is wet, the finish is the last question rather than the first and we would rather diagnose than decorate.
How long does lime plaster take to cure?
Weeks rather than days. Lime cures by carbonation with atmospheric carbon dioxide, not by hydration and each coat must be left before the next. It cannot be forced with heat and cannot be applied in frost. If a programme has no room for that, lime is the wrong specification and we will say so at drawing stage.
Does lime plaster crack?
It develops fine distributed crazing and that is by design - the plaster is deliberately softer than the masonry so it accommodates seasonal movement rather than forcing the brick face to spall instead. Free lime migrating into those hairlines partly re-heals them. It is not the same thing as structural cracking.
Can you work to a conservation officer’s specification?
Yes and we would rather see it early than price against an assumption. On listed buildings a breathable system is frequently a condition of consent rather than a preference and we are comfortable working to a heritage consultant’s or conservation officer’s stated build-up.