Gel Coat / epoxy compatability

General Composites Discussions Products Talk
#1

In my very small amount of experience, I’ve found epoxy to bond very poorly to parts made with polyester resin. I’m hoping to start making molded parts now, and will be using epoxy resin. I’d like to get the benefits of first spraying clear gel coat, and then laying up the cloth. Are certain gel coats compatable with epoxies? I know that low viscosity epoxies are often used for surfacing, but I don’t think that would work with curved parts. Are there any epoxy products that would serve the same purpose as the gel coat?

Thanks for the help,
Brian Wheeler

#2

Just thought I’d mention I posted a similar quesry in the composites thread. I’m going to try epoxy instead of PER and have been wondering exactly the same thing.

As far as I know epoxy isn’t generally compatibile with polyester resin though. I think the product you (we) want is often called epoxy surface coat.

#3

…

#4

If you are building pieces out of a mold, you can use a poly clear gel coat and then use epoxy. You will need to let the gel coat cure out fully first and then apply the epoxy, either through infusion or wet lay up. Couple points of caution here. There will not be any chemical bond between the two surfaces as it will be complete mechanical (basically glue). Epoxies can vary in there adhesion strength, so I would test your set up on a small piece first. Also, use little if no tack spray to set the fabric in place on the gel coat as this can lead to hazing below the surface of the gel coat. Also, if exposed to heat, you may find that the layers can separate. In conclusion, you can make parts this way, but be aware that there are many possible issues.

#5

I think your best bet is to use an epoxy based surface coat. I am not sure if there are any epoxy gel coats but any reputable supplier could send you in the right direction.