Rendering over cement particle boards

Cement particle boards or render boards are normally fitted on timber frame builds and then the rendering is normally carried out over the board. However there are a number of problems that could arise with cement particle boards if not fitted properly or if the incorrect render system is applied over it.

Most render manufactures state that their product can be applied over cement particle boards however from experience although that is correct I would advise that the render is kept as thin as possible, probably a maximum of 10mm in thickness. A lightweight render system is best suitable simply because it bonds better to the cement particle board and secondly it is more flexible.

The traditional render systems and the self-coloured scratched render systems are not recommended because they have to normally be applied at 16mm-25mm in thickness which is too heavy and slightest movement will cause cracks in the render.

Another tip would be to fit sufficient screws onto the render board, not fitting enough screws will mean that the render board will move slightly (even less than 1mm) and the render will end up cracking, you will notice the cracks when the render gets wet normally they are not visible during a sunny day. Also ensure that you use stainless steel screws because the rust will come through to the render over time if standard screws are used.