69 GM polyester or epoxy resin?

B

Bob Hollinshead

What type of resin was G.M. using for fiberglass reinforced molded parts back in 69? I've got some very rare pontiac parts to work on and I'm looking for a definitive answer if anyone knows. One part has a hack job repair that was done back in the 70's with only bondo that actually has held up just fine-adhesion was good suggesting to me that the part is polyester. The fiberglass repairs I've done on the pre-SMC cars always held up fine also leading me to believe polyester is 1969 fine. But.... with all the West Systems epoxy threads I've read here and a few other places I wonder if that's a better way to go? Still I wonder about expansion rate differences-I've seen many SMC spec'd repair materials show their ugly face when the sun is shining.
 
now i could be wrong but i dont think they ever used epoxy. it was all polyester, smc or maybe vinyl ester at one point. epoxy is somewhat new for composites. atleast newer than production cars in 69. i only use epoxy anymore for my glass work. not that i do alot of it anymore. the occasional vette, boat or ski repair. i am always using west system or equivalent. i use it with all my wood work as well. it takes longer to kick off but its easy to use with the pump dispensers, no odor and it works with any substrate even smc. its kinda like a no brainer really. just more expensive.
 
Jim, if I understand this right you're using the West system for all of it-the older polyester fiberglass and the newer stuff? I just don't want to have rate of expansion issues that might show. The pedestal mount decklid spoiler on this thing has a bow in it from age I guess so I'll have to make some cuts on the bottom sides to straighten it out, the hood scoops need some crack repairs and re-contouring to get the fit and shape right, and one of the fender vents has an old collision repair that needs to be done right... non replaceable parts.
 
I'm not Jim and his answer is spot on, however I would use epoxy primer over the sanded epoxy repair before anything else, as this is where a problem can easily occur, adhesion between epoxy repair and anything else. We would use vinylester resin in this case, so that would be another option

Dave
 
oh yes, i would normally grind out cracks etc, do the repair with epoxy and once all the actual glass work is done then i would put the whole car in spi epoxy primer and continue on with the job like it was any other car. epoxy primer then filler, ploy primer, 2k...and so on. also bob, yes when you use the west system you dont need to match materials like polyester with polyester or smc with smc. the epoxy wont show. everyone i know around here that does vettes just use west system across the board. i dont do a ton of them but maybe the 4 i have done in the past 4 years all still look great today. no shrinking around the repairs. one of them was black also so that sees some nice summer heat. even when you consider boats which is what the west system is originally designed for. boats are usually all polyester and the whole west system line is made to repair all that stuff and be stronger with no compatibility issues.
 
Thanks for the advice, West Systems it is then. There's some thin edges and intricate repairs so the added strength will be a plus for sure.
 
I've been using the West Systems and like it, the strength is impressive. The cure time is the only drawback I can see. The supplier I used told me to use regular polyester body fillers for final finishing with the only requirement being that the epoxy needs to be sanded which makes sense. Being that this stuff works over polyester fiberglass I wouldn't think there would be any problems applying polyester fillers over the sanded WS epoxy-or am I wrong on this?
 
Bob Hollinshead;42209 said:
I've been using the West Systems and like it, the strength is impressive. The cure time is the only drawback I can see. The supplier I used told me to use regular polyester body fillers for final finishing with the only requirement being that the epoxy needs to be sanded which makes sense. Being that this stuff works over polyester fiberglass I wouldn't think there would be any problems applying polyester fillers over the sanded WS epoxy-or am I wrong on this?
Click to expand...

Bob.....I have listened to the trash talked by the people who sell the West Systems and other products like it. In order to sell their products, they have gone way overboard to convince people that their product is the ONLY one to use. For me, I think this approach is not great as I really think West Systems are an excellent product and better than anything else available, just as they claim. We use it and others a lot with great success and like Jim says, it sorta becomes a nobrainer after awhile. However, we had 2 failures on show cars, one that was the most expensive paint job we have ever done by thousands...Both failures were over sanded, CURED West Systems. Of course, West systems said that we must not have sanded enough and we also used an inferior filler which was Rage. Everyone should make up their own mind, but the rule in this shop is unwavering...NOTHING gets put over CURED epoxy of any brand or style except another fresh coat of epoxy on a SANDED epoxy repair or coat. Also, I will really get hung for this statement, but we go so far as to say it must be sanded with nothing coarser than 150 grit as I feel a coarser paper could leave too much unsanded area for a proper mechanical grip...your mileage may vary....Dave
 
Thanks for the input, valuable experience shared there and sounds like you got some good rules in place to follow. I re-read Jim's post as well and see he recommended SPI epoxy over the West Systems repairs before anything else is applied. I've seen some people have adhesion issues when applying body fillers over some of the epoxy based panel adhesives. One thing for sure though-I never have any issues with anything when I spray epoxy primer down before regular bodyfillers are applied.
 
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