Hi Yoram

The hyrib mesh is like expanded metal mesh except that it has heavy grooves 3/8 inch or 3/4 inch, which stiffens the mesh. This allows us to do away with the plywood part - a plywood to stand up outdoors, marine plywood, is quite expensive even in this part of the world. Unfortunately, the grooves only run in one direction, so that is the purpose of attaching another piece along the back. I make a batch of slabs, even small 6 inch by 6 inch panels out of scrap mesh - you never know when you might use them.

I should also mention that there is precast fiber reinforced cement "board" for using in showers, etc. It is available in many hardware stores, it should be strong enough for fresco, is about 3/8 inch thick, and is a light grey color. If well soaked, it might be good for portable panels. I don't know exactly how they cut it - I would use a masonry blade in rotary power saw.