I don't have much choice in this application, not automotive, but how well does fiberglass hold on to epoxy primer? What time window do I have with it?
need a little more info here. what are you trying to do? a boat repair where you are laminating glass? what kind of resin are you using with your glass?
well typically in the fiberglass world you never put polyester over epoxy. only epoxy over polyester BUT for this application what your trying to do would be fine. of course epoxy resin would be better but also more expensive.
doesnt stick. it will stick reasonably well for something like that or when we put body filler on out cars but when it comes to making a structural repair like on a boat or fibeglass part, it would never hold up. the polyester would delaminate off the epoxy when under stress.
Wait - arent all/most body fillers polyester? We are told to put filler directly onto the epoxy primer - no scuff if within 7 days - and it will hold better than going direct to metal. Is this something different?
yes and no. does polyester body fillers stick just fine to epoxy primer yes but we are talking laminating resin and doing fiberglass work. body fillers stick just fine for what they are needed to do. body filler is under no stress and will have plenty good enough adhesion for us to do our bodywork and paint with. now if you had a boat and the hull was made with epoxy resin then you couldn't fix it with polyester. it will fail and delaminate. any kind of twisting or stress will pull it apart because they arent bonded together like poly to poly or epoxy to epoxy.