'72: Polyester or Epoxy Adhesive?

[Patricia Brown]

Hello. I'm new here but have recently discovered how helpful the archives are! I've been reading anything I can find about the different types of fiberglass and adhesives as it relates to my '72. It sounds like my car likely utilizes a combination of FRP and SMC.

Here's my question: A friend recommended to me Evercoat's "SMC Panel Adhesive" (#994), saying it would bond anything I come accross on the '72. The product description says "The only *polyester* adhesive strong enough to bond small SMC panels. Repairs small ares on SMC or fiberglass surfaces."

I have read many times that only epoxy is used on SMC panels, not polyester! And yet this product is specifically for SMC (as well as fiberglass). Can anyone explain what's going on? Thanks, Patricia

[Wayne W.]

Re: '72: Polyester or Epoxy Adhesive?

The Evercoat is a polyester based product. It has a high quality resin, but it is marginal as a bonding agent for SMC. The original bonding material on the 70s cars was also polyester based and it too was just marginal. As evidenced by the fact that when these cars get hit, they just explode at the seams. An epoxy product is a much better bonding agent. The Evercoat will do OK for filling and finishing.

[Patricia Brown]

Re: '72: Polyester or Epoxy Adhesive?

Wayne, thanks for the explanation. Would you recommend a specific brand/product line I should go with? I also read that epoxy is very unforgiving if you get your hardener-to-product ratio off; I am very concerned about that. Is there a sure-fire way to *accurately* mix product and hardner, other than by eye/experience (which I don't have!)?

I've also wondered about how to do repairs. I've watched the videos Eckler's offers on fiberglass repairs, and when they discuss SMC they specify to use a patch of SMC on the back of the repair and then fill in the front of the repair with adhesive. I've since noticed "SMC resin" available which claims you can repair SMC using mat and the special resin, just as you would repair std. fiberglass. Is either method proper? Will using the SMC resin and mat be as strong as a patch of SMC backing a repair?

Thank you! Patricia Brown

[Steven S.]

Re: '72: Polyester or Epoxy Adhesive?

There are several ways to build a polyester resin including adding an epoxy resin to the system. The old, origianl fiberglass resins did not have epoxy in them. The bonding adhesives were made with basicly the same resin systems. When SMC can into play, it was a completly different animal and needed different bonding adhesinves. Sounds like the one you have found is taking advantage of both technologies and works on both.

Steve