rruff
Explorer
I don't think the type of cloth is a big concern, but I'll tell you what I'm using. One layer of 17oz 45/45 biax, one layer of 10oz 0/90 biax (both from Fiberglass Supply), and top layer of a very tight plain weave 6oz cloth (from Fiberglass Site). The biax is unidirectional cloth that is knitted together. I'm using it because it's a little stronger and stiffer than plain weave and it comes in diagonal (the 45/45). Combining this with the 0/90 biax and the plain weave gives me more isotropic strength/stiffness properties in all directions. The main reason for the 6oz cloth is that it gives a very nice finish, almost like peel ply. The other stuff leaves a texture that's hard to smooth out (takes more filler).
Note that I have 33oz/sq yd of fiberglass and epoxy it's about 72oz/sq yd /9/16 or .50 lb/sq ft for each skin (before paint). In my destruction tests I found this amount was what it took to satisfy me. I could hit it hard with small sledge hammer and it held up fine. IMO impact resistance is the most important factor for determining how much cloth to use. You can certainly use less but it will damage more easily.
Thank for that link to the "Pod" build! I was looking for that recently and couldn't find it. As I recall at the end of his build he pulled it out into the sun and he promptly got delamination bubbles on top, just as bahndo described. Back a few years ago when I started building with XPS foam, I did some research and found that surfboard makers have had this issue as well. On the other hand some people have not reported problems. There are some panel manufacturers who use XPS. It's possible that texturing the surface helps but I really don't know. I put some samples out in the sun and did not get any delamination, but I still decided to switch to PVC foam when I resurrected my build. It is much stronger than the light XPS (and twice the density) and epoxy bonds to it very well. I think the biggest reason for the better bond is that the cells are much larger. When you cut or sand it there is a microtexture from the cut cells.
Note that rolls of fiberglass are typically 50" wide, and if you have a dimension larger than this you'll need to overlap each layer of cloth ~2". You don't want overlaps on top of each other; you'll need to cut and arrange your pieces to accommodate this.
Don't worry about the corners; you can do those last using several layers of light weight conforming cloth. Just make sure your edges (inside and out) are very well rounded.
Get "tape" for the edges, and joining pieces together. They are at the bottom of the USC page you linked.