Plastic bag will bond to epoxy and epoxy will yellow w/sun. better to use a good fiberglass resin like west systems. (will not yellow) https://www.westsystem.com/ use mylar plastic sheeting https://www.amazon.com/Transparent-Myla ... B01BH76J36. Wax mylar with automotive paste (2 coats) then place wax side down against resin supported with thin flat wood or similar (clamp) and let fully cure. Will leave resin smooth and will not bond.
I work in the Marine industry doing fiberglass repairs specifically with West System 105 and G-flex. Both epoxies DO NOT stick to LDPE/HDPE (zipock and almost all other no-name brands) bags or any other polyethylene plastic. Actually, nothing does. If you come up with something that does bond to Polyethylene, you are rich enough to never have to work again in your life. If you look up the industrial processes and few chemical treatments for doing this, you will understand how difficult this plastic is to bond to. My only idea of why you may have experience epoxy sticking to new plastic bags is if you had some folds in the covering piece of plastic. This would "lock" the plastic in to the repair. I Even use "Saran wrap" as a smoothing cover to eliminate some sanding in the finished repair/coating.H2Oaltitude wrote: ↑Tue Dec 19, 2017 5:17 am
Plastic bag will bond to epoxy and epoxy will yellow w/sun.
For low heat build up instances like the OP's repair, waxed paper (next to the aluminum foil and saran wrap in the grocery store) is the way to go. It is pretty stiff for keeping contours (don't use on compound contours). Only when extreme heat is applied, is wax paper a no-go. So if your pour is going to get hot (about 3x3x3 cube of epoxy in your repair), the wax will melt and the epoxy will infiltrate the paper. This is not a big deal if you are sanding anyway, but wax paper will not leave a finished surface if heated too much as some of the paper will remain behind. Also make sure that if you are using external heat to make the epoxy set faster, you will likely not get a good finished surface with waxed paper.H2Oaltitude wrote: ↑Tue Dec 19, 2017 5:17 am
......use mylar plastic sheeting https://www.amazon.com/Transparent-Myla ... B01BH76J36. Wax mylar with automotive paste (2 coats) then place wax side down against resin supported with thin flat wood or similar (clamp) and let fully cure. Will leave resin smooth and will not bond.
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