You could probably just mold the hinge area on the underside instead of the whole underside, that would be a lot cheaper and easier. Then attach the two parts with epoxy.
The PVA i was talking about isn't resin, it is what you put on the mold before you lay up your CF so that it will separate from the mold
You can pretty much use CF/FB (If you go with FB would recommend S-glass, much strong than regular E-glass, almost as strong as CF, quite a bit cheaper)
For your final parts, definitely use 2 part epoxy, much stronger and better bond than other resin.
The stuff I used was honeycomb (looks literally like bee honeycomb), which is outrageously expensive, but you saw the white foamy stuff, which was just high density foam. It achieves the same thing in the end, making a sandwich composite.
For your mold, you want it to be stiff and cheap, so you should use fiberglass mat/poly resin.
Just a VERY quick guide on how to make a hood to get you a picture:
-coat stock part (hood) you want to replicate in wax, wax, wax. Along the edge, attach plastic (coroplast or something) on the underside, then fill in the gap between the plastic and the hood with clay. Cover the whole thing in PVA.
-brush on poly resin nice and thick, try to let it gel a bit. add first layer of fiberglass.
-add more poly resin, add more fiberglass, til you have 6-7 layers. You will probably want to fiberglass sticks of wood in or whatever to stiffen it up as much as you can (for big objects like a hood)
-once it's all cured, you can wedge the mold away from the hood, now you have your mold, and you have a nice flat edge around the outside (from the plastic you attached to the hood) so you can have an oversized part that you cut down to stock size.
to make the final part:
-wash the mold, wax, wax, wax, PVA. (don't wax the outside edge)
-coat mold in epoxy resin, then lay in CF.
-lay honeycomb or foam sheet in, then coat again in epoxy resin
-lay a layer of CF, make sure it is wetted through, add more epoxy if needed
-lay perforated plastic over wet cf, then cotton absorbant over that
-cut a large sheet of plastic to cover the mold, stick/tape to outer edge you made and didn't wax
-attach vacuum pump
-wait for cure
-pop part off mold, wash.
that is really brief and there are a ton of little steps in there and lots of measuring/cutting. There is a really good write up in the link I sent you that goes into a lot more detail, including materials you will need.
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