Fiberglass resins

[Bill Musarra]

I am starting to do some fiberglass work on my car(DRB#5) and after doing some research, have come up with some questions. When these cars were manufactured, what type of resins did they use in their builds. Was it polyester or epoxy? In my readings I came across some information that make it relevant. Acording to what I read, if you have polyester resins, it can be repaired or added to, with either epoxy or polyester. If you have epoxy on the other hand you have to use epoxy. If you use polyester on epoxy, it will seperate after a couple of years. They also said that when you sand it, or rough it up, that epoxy smells like epoxy and polyester has a chemical like smell. Care to comment on that?? What do you guys know concerning these findings?? Should I just use an epoxy just to be safe?? It is a little more expensive.

Bill

 

[Randy V]

Bill - So far I've been using West System's Resin which is Epoxy based. No real smell to it either! Yes a bit more expensive but stronger than the others in the limited testing I did.

 

[Jack]

Probably 99% of the fiberglass bodies out there are manufactured with either polyester or vinylester resin based. Epoxy works well with either, as does the above mentioned resins. As Bill mentioned, you would use polyester resin on an epoxy part, although with good prep you may get away with it on vinylester. Big difference is the peel strength of the laminate you are adding, or secondary bonding in sheer.

 

[Ron R.]

West systems has a great rep, btw.

 

[Dwight]

I'm interested in this thread. I have some fiberglass work to do on my RCR. What is the correct resin to use?

Dwight

 

[Al Wohlstrom]

Most all the fiberglass bodywork we work with is polyester resin. As Bill said you can use either polyester resin or epoxy resin, but once you use epoxy resin on a part you have to stay with epoxy. You can put epoxy resin over polyester but not polyester over epoxy. Epoxy is quite a bit more expensive and with the parts I've made I'm happy with polyester. Most all body fillers ( Bondo, Evercoat Z grip, Evercoat kitty hair etc) are polyester resin base, so if you intend to make a finished part you will need the use one of these. Boat suppliers have epoxy resin base fillers but with the word "boat" involved they are very expensive. I like working with fiberglass, the only downside is the dust when sanding, get a good respirator.

 

[Jim Rosenthal]

Bill, polyester is good for original layup, and cheap, but for repairs you should use epoxy or vinylester. Polyester is a good construction resin but a lousy glue- it doesn't do secondary bonds well, and isn't very strong in that application. The marine folks are more knowledgeable about this than the auto people- they deal with this all the time. For surfacing and cosmetic stuff you can use Bondo etc, but for a structural repair you want a stronger resin and that means epoxy or vinylester.

The body parts of my GT40 were made using polyester and even though new had numerous cracks and structural voids in them- they wee poorly made. We did the repairs and reinforcements with vinylester (3M) and have been happy with it. It is easy to use and very durable. For repairs on my boat, which I've had 22 years now, I have always used West System epoxy, and have been very satisfied with it. The people who make it also publish a lot of very good and inexpensive manuals on how to use it and perform various repairs and layups.

 

[Tom]

I'm interested in this thread. I have some fiberglass work to do on my RCR. What is the correct resin to use?

Dwight

Dwight,
I asked the same question a few years back. Fran stated then they use Vinylester resin.

I use West Systems Epoxy and various fillers for everything except large molds. For those projects I use polyester laminating resin and tooling gelcoat to keep the costs down.

Tom

 

[Tom]

Bill,

look at the unfinished side of the fiberglass. If it is matt fiberglass (likely), it is a polyester or vinylester based resin.

Tom

 

[Jack]

For polyester or vinylester constructed bodies, my choice for repair or modifications
would be vinylester resins. Polyester will do if prepared properly too.

Most of the parts that I have made over the years used these resins successfully.
If you do carbon fiber repairs or parts, epoxy is best for structural components and vinylester is satisfactory for non load bearing components. IMO, of course.

 

[Dwight]

Thanks
I plan on moving the wiper to the driver (American) side of the car. I do plan on driving it long distance and I know it will rain.

Dwight