SIP Eco Panels consist of a layer of insulation sandwiched between 2 sheets of OSB board. These panels are often referred to as SIPs, which stands for structural insulated panels. They are becoming more and more common on building sites because they allow the builder to achieve good u-values and excellent airtightness, but also the panels can be erected very quickly which dramatically decreases the build-time.

So how are SIPs panels finished? Well, on the whole, they are finished with a thin coat render system. We always recommend a breathable silicone or mineral render, to help allow water vapour to escape. In this blog, we are going to describe the installation process to provide a perfect rendered finish!

Installation Process of SIPs

With the SIPs panels in place, we recommend hanging a waterproof breather membrane over the entire surface of the panels. Something like DuPont Tyvek Housewrap works pretty well – this membrane should be secured with galvanised nails or staples at 600mm centres horizontally and 300mm centres vertically.

Once the membrane is in place, vertical battens need to be fixed onto the SIPs panels. The positioning of the battens will depend on the render carrier board used, since the battens need to support the render carrier board that get attached on this.

We normally recommend the 12mm Econic render carrier boards since they are relatively good value and they can be scored and snapped. The boards measure 2400 x 1200mm in size and require vertical battens to be positioned at a maximum of 600mm apart. The battens should be 75mm wide, to allow plenty of space for two neighbouring boards to be attached. We recommend a 5mm gap should be left both vertically and horizontally between adjacent boards to allow for expansion.

Once the render carrier board has been fixed to the battens, you are then ready to apply the basecoat layer.

Applying the basecoat to the render carrier board is then relatively easy – we recommend using EWI-225 premium adhesive. The EWI-225 is both strong and flexible and so ensures a long-lasting finish when applying the render to the SIPs boards.

EWI-225 Premium adhesive is a dry mix and needs to be mixed with 5.5 litres of water prior to application. Once the adhesive has been mixed with water and the white putty has formed, it needs to be applied to the render carrier board with a notched trowel. We recommend using a 10mm notched trowel, this is the best size of trowel to apply a 6mm layer of adhesive to the cement board.

Once the adhesive has been applied, the fibreglass mesh needs to be embedded within it – it is this mesh that gives our render systems such flexibility. EWI-640 Reinforcement mesh comes in 50m2 rolls (1mm wide), and this needs to be applied in vertical strips within the adhesive.

The strips of mesh need to overlap one another by 10cm at edges and this needs to be sunk within the layer of adhesive – this can be done by using the flat edge of the notched trowel and drawing this up from the bottom of the wall – this will pull the adhesive through the holes in the mesh. Allow the EWI-225 at least 24 hours to go off before applying the render.

Applying render to SIP Eco Panels

You are now ready to apply the final top coat render (EWI-225 premium adhesive does not require priming, prior to applying the render).

For all our EWI-Pro thin coat renders, the thickness of the layer is determined by the size of the granulate in the render. For example, EWI-040 Silicone Silicate render comes in 4 thicknesses, 1mm, 1.5mm 2mm and 3mm. The layer of the render should therefore be either 1mm, 1.5mm, 2mm or 3mm depending on the render used – it should be no thicker!

This is really important to remember, and will ensure the finish is good. We have heard several reports of people applying the render too thick, and not being able to achieve the required finish. With that in mind, apply the render to the SIP Eco boards with a trowel and then pull off all the excess with the trowel. Once you have taken off any excess, leave the render for 5 mins and then, using a plastic float, work the render in a circular motion to give the final textured finish.