We recently had an interesting enquiry from a customer about how you would go about rendering plywood. It’s a tricky question, because plywood really isn’t an ideal substrate to render onto, however sometimes it’s unavoidable. There are solutions for applying render to plywood, and we’re going to talk you through the best way you can do this!
Rendering Plywood: Render Carrier Board
When rendering any substrate, especially when rendering plywood, consideration needs to be taken as to the suitability of the substrate for the materials that you are using. Plywood is not particularly waterproof and will inevitably absorb water from the basecoat, which can cause the wood to warp and therefore hinder structural integrity.
To avoid this, render carrier board is an ideal solution, but the downside is that it can’t be applied directly on top of the plywood. This is because the fabrics need ventilation to allow moisture to escape and to avoid a situation where water builds up between the two materials; an air gap between the two is needed for the reduction of condensation. To resolve this, the best course of action is to staple a breather membrane to the substrate, before installing timber battens on top of the ply; the positioning of the battens will depend upon the size of the render carrier board you are using.
Once these are in place, you can secure the render carrier boards on top of the battens and attach them with wood screws. The spacing of the boards will depend on the type of render carrier board you are using, however generally you would leave 4-5mm between each board. After the boards are in place, the gaps between them need to be covered over by a render carrier board tape; we tend to recommend the Pavatex render carrier board joint tape because it’s basically an extremely breathable self-adhesive membrane which prevents water vapour from gathering in between these gaps.
Basecoating the Render Carrier Boards
Render carrier boards don’t require priming because they are specially designed for being rendered, so you can go straight into applying the basecoat with no problems. Although it is possible to use the 220 Basecoat Adhesive, we recommend using the 225 Premium Basecoat as a basecoat for extra strength and breathability. At this stage, the necessary beading required for the structure is sunk into the basecoat along with fibreglass mesh – remember to overlap each strip of fibreglass mesh by about 10-15cm.
Once set for a period of 24-48 hours, the basecoat needs priming before rendering. The type of primer you use will depend upon the type of render; for example if you were to render using Silicone Render (we recommend this one for constructions that require a high level of breathability), you would need to use our SiSi Render Primer. This can be painted on and then left to dry for 12 hours.
Rendering the Basecoat Layer
After all of that essential preparation, you are finally ready to render. Using our ready-to-use Silicone Render, apply it to the substrate using a trowel at a thickness that matches the grain size of the render; for example, if you’ve chosen a 1.5mm grain size finish then you should apply the render at 1.5mm thick.
Once applied, rub up the surface of the render with a plastic render float to bring out the texture and achieve a consistent finish, then leave to dry for 24-48 hours.
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