Outdoors
Outdoors a render has to stand driving rain, frost and sun — and, on an old wall, let out the damp rising from the ground. That is why lime remains the facade render par excellence: it protects without trapping. A sealed render can last, but on stone or brick it traps water behind it.
The test
Included: renders and stuccos whose exterior verdict is “exposed” or “sheltered”. Sheltered means under an awning, porch or gallery, out of direct rain.
RenderHydraulic lime (NHL) · 1–3 mm
A material rather than a colour: one to three millimetres trowelled on, giving the wall a relief and a depth no paint imitates.
Photo Jules Verne Times Two · CC BY-SA 4.0 · Wikimedia Commons
RenderCement + resin · 2–3 mm
A mineral render as one continuous surface with no joint anywhere — the only finish here that runs from floor to wall in a single material.
Photo Alex van Olst · CC BY-SA 4.0 · Wikimedia Commons
StuccoAir lime (CL) · 1–2 mm
The everyday Venetian stucco: two coats compressed with the blade, closing the surface without taking it to a shine.
Photo Kubko666 · CC BY-SA 3.0 · Wikimedia Commons
StuccoHydraulic lime (NHL) · 3–6 mm
The one lime finish that takes running water — and it is the soap, not the lime, that makes it waterproof. The floor of hammams for centuries, walls and floors alike.
Photo Eigenheym · CC BY-SA 4.0 · Wikimedia Commons
Among paints, these pass the same test: Eau-forte, Badigeon de chaux, Peinture à la chaux, Peinture au silicate, Peinture à la farine, Peinture acrylique.