Re: Fibrex Board
I wish I could help you out with that, but I'm not familiar with the product. I may have a piece that is similar to what you're describing, but I think it's called tile board here in the states, and it's only 1/8 inch thick. It's a cheap paneling-like material one might put up in a bathroom. I have two large sheets of it, 4'x8' that I plan to paint on. They're covered on one side by what I think is melamine, what is a hard plastic material. I plan on gessoing the brown side and painting on that. I'll have to build a support for it, as I plan on painting a piece about 48"x38".
The brown side is probably Masonite. I don't know how it's manufactured, or the composition, but I plan on using it anyway. I think the plastic side will provide good protection against moisture. It's not something I bought specifically for painting, but it's otherwise going unused. I don't know if this helps or not, but just thought I'd let you know there's someone else thinking along the same line.
"A bold failure is better than a timid semi-success." John Howard Sanden