A renovation plaster does not stop rising damp: it gives the moisture somewhere to evaporate and the salts somewhere to crystallise, away from the surface you look at.
On old masonry with rising damp, the temptation is to seal it. That is the costliest mistake: the water does not vanish, it climbs higher and re-emerges a metre further up. Renovation plaster does the opposite — it is macroporous, full of air chambers where water evaporates and salts deposit inside the thickness instead of on the visible face. It does not cure the cause: it is a therapy that buys time while the cause (drainage, barrier, a leak) is solved elsewhere.
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
The detail of the crafta metre above the stain
Complete removal of the failed plaster to a metre above the damp line, raking out the joints and brushing off the salts.
The stain is where the water leaves, not where it reaches: strip a metre higher and sleep easy.site notebook — editorial synthesis
The rule that governs everything
This is the principle that holds a renovation together: moving outwards, permeability must increase, never fall. A single layer tighter than the others becomes the point where everything stops — and where everything blows off.
It applies to the whole build-up, paint included: it is why a washable paint cannot be used on a renovated wall, however convenient.
What it cures and what it doesn't
Renovation plaster manages the effect — evaporation and salts — but does not touch the cause. If water keeps arriving, sooner or later the system saturates: how long it lasts depends on how big the problem upstream is.
Before plastering, always look for the origin: a broken downpipe or a back-falling pavement can be fixed in a day and is worth more than the whole build-up.
It depends how much water keeps arriving: if the cause remains, the macropores gradually saturate with salts and the system loses effectiveness — usually a horizon of years, not decades. If the cause has been solved, it lasts like any good lime plaster.
They are two different things and often go together: the barrier (injections or a mechanical cut) interrupts the rise, while the plaster manages what remains in the wall. On very thick or irregular masonry the barrier is not always effective, and then the plaster becomes the main defence.
Yes, and it is often necessary: if you only renovate inside, evaporation concentrates outside and the damage moves there. Outdoors, though, you need a finish that resists driving rain while staying permeable.
From the datasheet: it must declare high porosity, low capillarity and vapour permeability, with the European classification for renovation plasters. Generic lime plaster breathes but lacks the macroporous structure that holds the salts.