wyowindworks

Glenn, for large parts I would recommend using a low viscosity resin. Something like Proset 117LV. It has viscosity of 320 cps. If you use a slow hardener you can warm the resin and mold during infusion to further reduce the viscosity (150 cps) and still have adequate infusion time (100 minutes). The downside to the slow hardeners is that you will have to heat treat/post cure the part to get the resin to fully cure. Something like 125*F for 16 hours will get the job done. Another option is to use vinyl ester infusion resin. This is really low viscosity stuff and won't require a heat treatment/post cure. It's not quite a strong as epoxy but wil have a higher HDT with a room temperature cure. The downside to vinyl ester is that it has a short shelf life (3 months).

Window screen material can work but it can be rather slow. Adding two layers can help. Better yet, use a proper flow media. Also stretch bagging film like Stretchlon 200 can be rather problematic. First off, it's notorious for leaking. Secondly, it will stretch into voids in the flow media and slow or stop the infusion. You do want to be careful of infusing too quickly. If you go too fast you will have pinholes on the surface. I like to use an aggressive flow media but throttle the flow rate by using a smaller infeed line.

You typically want to pull above 28" Hg. You want to allow the laminate to be under vacuum for several hours before infusion to boil off any moisture. You also want to make sure that your bag isn't leaking anywhere. If you have a small pinhole anywhere you will draw air into the laminate and have voids and pinholes.