Help & Advice
A render finish is one of the more popular options for cladding on ICF walls. The type of render system that Polarwall recommends is a modern two coat render finish. The render is made-up of a cementitious adhesive basecoat into which a reinforcing mesh (of either alkaline resistant fibreglass mesh or a polypropylene mesh) is trowelled. Once the base coat has set, the through-coloured top coat is applied.
Of these modern render systems there are two versions available. One is an acrylic based render and the other is a silicone based render. The silicone render has a couple of advantages in that it sheds moisture and dirt much more efficiently. It is also a flexible material than the acrylic based render. This flexibility is important, due to material expansion and contraction as temperatures change..
As with any building material there are good render systems and not so good render systems. Dont be fooled by cost alone. A good render can be placed much thinner than a render using cheaper ingredients.
Traditional cementitious renders are not recommended for use on ICF. This is because cementitious renders shrink and move far more than the XPS material.
Our recommended render for ICF walls
A render product that is very popular with some of our builders is the Parex render system. This uses their Maite base coat and their Siloxine through-coloured silicone top coat.
The textured surface on the Polarwall XPS insulation boards is specifically designed to bond to concrete and cementitious products. In a recent test using the Parex Maite basecoat, the pull off strength of the render was 50% greater than the same basecoat tested on expanded polystyrene.
The bond strength was equivalent to a pull off strength of 38 tonnes per square metre.