What are the pros and cons of using 2 layers of 210gsm against 1 layer of 416gsm, apart from price and ease of forming :-) ?

Thanks for reply Here is the mould I will be using :-) Additional layers and reinforcing ribs will be added where extra strength is required.

I discussed the advantage of alternating the weave direction with Simon at SHD. He said that this should only be done if there are more than two layers in order to avoid uneven stresses. A bit like plywood construction. IE using three layers the outer layers would face the same way with the middle one at 45 deg.

The main reason for trying to use a single layer is the big reduction in cost, almost halved :-)