Polyester resin vs gel coat

[Jamie]

I did a quick gel coat repair on one of my carbon fiber old town's using clear gel coat that I ordered from Nova Craft. Due to shipping restrictions NC could not supply the catalyst and simply suggested Bondo hardener from local stores. Of all the canoe repairs I've done, this was by far the easiest...

​The one thing I noticed is the "Gel coat" provided cured, sanded and acted just like cheap (Bondo) polyester resin. It was great to work with. Since the catalyst used is the same it got me to wondering if there is a significant difference between proper gel coat and the cheaper alternative of polyester.

​For any future clear gel coat repairs, will polyester work as a replacement to ordering proper gel coat?

 

[stripperguy]

As far as I know, gel coat is polyester resin.
When a production boat is made in a female mold, the gel coat goes in first, directly against the waxed and mold release coated mold. This resin is a laminating resin.
Polyester resin will not cure on the surface in the presence of air. Some polyesters resins have a surfacing wax added, to allow a cure in the air.
Gel coat, since it is against the mold, does not have this surfacing wax.
With that said, a gel coat sold as a repair kit, will likely have some surfacing wax in it, since the resin would be exposed to the atmosphere.
You can buy laminating polyester resin, and then add your own wax to it. The wax is available at most polyester resin supply houses...
Merton's has polyester resin at $27.50/gal

 

[Canotrouge]

I hate working with gelcoat. Polyester resins of nay kind for that matter!!

 

[Odyssey]

So I could just patch my gel coated canoe with a little Bondo and some wax paper??

 

[Alan Gage]

So I could just patch my gel coated canoe with a little Bondo and some wax paper??

I've never done much with bondo but it's not recommended for marine repair. I believe it absorbs water and comes loose. But the activator for bondo and polyester resins are the same.

Alan

 

[Guest]

I hate working with gelcoat. Polyester resins of nay kind for that matter!!

I hate the idea of working with gelcoat too. So much so that I’ve never even tried it. I know there are different kinds of gel coat that require different applications, and I (may be wrong) think that some can air dry. And other than white I have not seen many DIY gelcoat repairs that really color matched.

Back when I didn’t know what I didn’t know I used polyester resin (and glass) from the auto store. This stuff:

http://www.autozone.com/sandpaper-a...ial/3m-1-qt-bondo-fiberglass-resin/167023_0_0

That stuff cured fine left exposed to air. It would also get hot-in-the-pot if I made too big a batch or miscounted drops of hardener, and I accumulated a couple of shop hockey puck reminders made of polyester resin, one with a brush stuck in it like a fly in amber.

Also note that while polyester will adhere to polyester, sticking to existing Vinylester or epoxy resin may yield different success.

And yes, Bondo is not a good solution for most boat repairs; it does not flex much if any.

 

[sailsman63]

Gel Coat is a little different from standard polyester resin. It is waterproof and sealing, while poly resin (Especially any of the auto-body stuff) is somewhat water-permeable. Ever seen an old-school fiberglass boat with glassed-in wood battens, spacers, etc? Most often, they end up completely rotted out, even when encased in glass and resin on all sides. This is one of the reasons that strip canoes, and Stitch and Glue boats are usually done with epoxy.