We used 6mm Marine ply for our restoration project for the sides only. It gives the Meranti something to bond with and provides more rigidity than 3mm.. The 3mm ply us too flexible for sides. However, for the roof we used 3mm. Its flexible enough to form the curve of the roof.
WHen I looked into building my Cino Vardo, I looked extensively into which grade of plywood to use and spoke with the technical people at Austral Plywoods who manufacture all classes of plywood in Australia.
The bottom line is that you only need to use marine ply when what you are building is below the waterline. As long as the ply is what is called Type A bonded and preservative treated, it can be used for exterior building. The best for exterior structures is what is called Premium Structural and starts at 6.5mm thickness. It has a BB surface finish, which is very good for paint finishes. I used this grade for my walls, especially as the van is only single skinned. The added feature is that this ply comes in longer lengths of 2700mm by 1200mm.
I used a 4mm AC grade exterior plywood for the roof, because I did seal that on the outside with calico material and about 8 layers of paint!! The A side is the interior "seen" side.
In all, I am pretty confident Cino Vardo will outlive me and probably the next owners!
Last Edit: Aug 25, 2020 21:34:40 GMT 10 by Roehm3108