SonexBuilders.net

Hey guys,
I need to do some rework to my wingtips. I will need to extend the top flange for edge distance, and lay some plies between the flange and skin to keep the skin from being pulled down. I have some bondo brand resin we bought for Matthew's hovercraft project. The label says polyester polymer. Dare I use it here? I am more of a sheetmetal guy so advice is welcome.

You are probably fine using polyester resin on the wing tips. If it were structural you'd want to get some epoxy resin.
Once original resin has cured, the only bonding will be mechanical (gripping nooks and crannies) not chemical (molecular). Epoxy bonds better than polyester mechanically. But for your application it should be sufficient if you rough the surface sufficiently.

Bryan
Sonex fibreglass parts are polyester. Polyester resin bonds to polyester fine. Just never use polyester resin to repair epoxy. As John said it needs to be ground back for adhesion, Make sure you remove the gelcoat.
Steve
Sonex 892

The only downside to working with the typical polyester resins is that they have an incredibly short working time. Like just a few minutes. So make sure you have everything cut and ready to go, and if it is going to take some time to do a large or a long area, plan to mix small amounts of resin and do it in multiple small areas. Laying peel-ply over the area will give fantastically smooth results and require much less filling or sanding.