Light Weight Render Systems

Thin coat render, over what is already there

A light weight render system is a thin coat system: a mesh-reinforced base only a few millimetres thick, then a coloured top coat. The point of it is that it goes on over an existing wall — over old render, over dash, over a tired elevation — without hacking anything off and without loading the wall with weight.

The build-up is usually an adhesive base coat with an alkali-resistant fibre mesh bedded into it, then a primer, then a through-coloured silicone or acrylic top coat with UV-resistant pigments. The mesh is what makes it flexible and anti-crack: the wall moves, the render moves with it, and hairline cracking does not telegraph through.

We have used the Wetherby and Ecorend systems on the Island. Both come in a wide colour range and in more than one texture, so the finish can be matched to the building rather than the other way round.

Light in weight, not insulated

Worth being clear about, because the name misleads people: "light weight" here describes the render, not the thermal performance. A thin coat system adds very little weight and very little thickness to a wall, and it will not insulate it.

Insulation is a different system. External wall insulation fixes an insulation layer to the wall first, and then a light weight render goes over the top to seal and finish it — so the two get used together, which is where the confusion comes from. If it is the warmth of the building you are after rather than the look of it, that is the page you want: insulated render systems (EWI). If the walls are solid and there is nothing to insulate into, spray cork is the other route.

Where it goes

Most of our thin coat work is a refurbishment: an elevation that has blistered and lifted, or a dashed house that the owners have stopped looking at. It goes over dry dash and wet dash as well as over sound render — the Colby job kept its dash entirely and still changed completely — and it takes the exposure on a coastal wall, which is what put it on the house at Lag Birragh on Onchan Head.