There are lots of different types of render carrier board (RCB) available here in the UK, and EWI Pro systems are suitable for use on all of them.

Render carrier boards are often used on timber frame or steel frame buildings to provide a surface on which a decorative render can be applied. These boards are designed specifically for the application of renders, whether it’s a thin coat system or a monocouche system.

In today’s blog post, we’re going to be talking about how you would go about applying an EWI Pro render system to a render carrier board substrate.

Why use Render Carrier Board?

Different render carrier board manufacturers create boards with different properties, however carrier boards are often characterised by high tensile strength which resists bending to prevent cracking and deformity, they tend to be breathable – so very suitable for breathable render systems, moisture resistant and non-combustible. RCB’s are designed to withstand weathering and impacts, so you can be confident in the security of your property and render system.

You will typically find that the render carrier boards on the market come in two thicknesses of 9mm and 12mm; however we recommend using 12mm render boards where available to ensure extra strength and stability (Blueclad, for example, only do a 10mm board).

Using Render Carrier Board Joint Tape

The render carrier boards should be attached to either wooden battens or a steel frame in a staggered formation. Each board should also have a 3 – 5mm gap between them and their neighbouring board.

Once the boards are attached to the timber/steel battens, it is time to mesh the joints. For this purpose, you can either use a breathable render carrier board joint tape (Pavatex offer a good one) or you can use our Fibreglass Mesh with tape. To do this, cut 200mm strips of our EWI-66640 Fibreglass Mesh, using an approved fibreglass mesh tape to hold these in place.

Applying the Basecoat to the Render Carrier Board

Because render carrier boards are designed specifically for the application of renders, you do not need to use a substrate primer. Instead, you can skip straight ahead to applying the basecoat. We suggest using the EWI-225 Premium Basecoat for this purpose. The EWI-225 is incredibly strong and offers excellent adhesion to the carrier boards due to the fact that it has fibres within the mixture.

Apply the EWI-225 to the render carrier boards using a notched trowel to a 6mm thickness.

Using Fibreglass Mesh in Render Carrier Board Systems

Once the basecoat has been applied, the EWI-66640 Fibreglass Mesh should be embedded within it. The mesh is embedded in the basecoat from top to bottom rather than horizontally from side to side. You will notice on the rolls of EWI-66640 Fibreglass Mesh there are markers at each end – these signify the 100mm overlap required when embedding the layers of mesh. They should always overlap the previous piece of mesh embedded by 100mm.

Once the EWI-225 Basecoat has gone off, you will need to prime the basecoat with a render primer. For example, if you are using our Silicone Silicate Render, you would need to use the EWI-333 Silicone-Silicate Primer which can be applied by paint brush or roller. If you are using a very vibrant colour, then we can tint the primer to match the render so as to achieve extra opacity.

Applying Render to Render Carrier Boards

Once the primer has gone off after about 12-24 hours, you can apply the top coat render. This is the decorative layer that ensures the render system is completely weatherproof and hydrphobic. You can choose to use one of our silicone renders, either EWI-075 Silicone Render, EWI-040 Silicone Silicate Render or EWI-076 Premium Bio Silicone Render, which are through-coloured renders.

This means they arrive pre-coloured in the same way that a paint would (so you don’t need to paint the wall after to achieve a decorative finish). The silicone renders are also breathable and hydrophobic, which means that they are capable of self-cleaning, so your maintenance costs will be significantly lower.