Epoxy Or Polyester?

centerline · Feb 24, 2014

Jongleur said:
I have a crushed and frayed edge of my boat.
It's about 6 inches long. At the bow, the
PO probably dragged the anchor over that section.

Glass fibers are sticking out and some of the
epoxy or polyester resin has crumbled out.

I can fix it, but I need to know what to use.
Would epoxy or polyester resin adhere better
to what the boat was made of?

if you are going to do it right, use polyester... if you are only going to put a forever patch it, use epoxy.

keep in mind, if you use epoxy, it will be harder to do a proper patch later if you decide to, cuz epoxy doesnt like stuff trying to stick to it.... whereas polyester doesnt care.

epoxy will take hours to set up... polyester will take minutes....

as for working with one or the other, the epoxy has a longer "open" time so you can do more area, but polyester sets quicker, so you can work it down with tools and apply some more... any mistakes made can be rectified quicker.

the whole project will be quicker task from start to finish with polyester....

epoxy is stronger and waterproof... but the rest of the boat is polyester, so do you think you need stronger or more waterproof for that little repair?

caguy · Feb 24, 2014

Do you have a bow roller? I amazes me how many midsize boat do not have bow rollers. It's one of the first Mods I did on the C-27.
On the cabin corner just above the head the gel coat was breaking. It looks as if there was an air pocket in the corner when they layer the fg over the gel coat. I had to inject resin under the corner to fill in that which was still intact. I shaped the rest of the broken areas and then covered with gel coat.
Check to see if the rest of the gel coat that is left is well supported.
Resin is easier to paint if you go that way. Epoxy can be painted but it really has to finish curing and then be thoroughly cleaned for the paint to stick,

Merlin Clark · Feb 25, 2014

There are different hardeners for the better epoxy systems and West System fast hardener will kick in around 10 minutes depending on the outside temperature. You'd want to wipe it down with acetone to remove the blush.
That's all. Nothing special. Epoxy sticks to everything, better.
I'd follow your friends advice. Maybe let him show you how it's done cause there are little tricks that we all pick up along the way. A few people here are more than happy to give advice on stuff they've never done but read about on the internet.
There is a saying among the guys I know that do this stuff for a living "build with poly and repair with epoxy". Most boats are built with poly because it's a lot cheaper.
If you go to the West System (NOT West Marine) site, there are complete handbooks on how to do just about any repair.

Sailvayu · Feb 25, 2014

The boat is built with polyester so I would use polyester. Epoxy has poor UV resistance so if you use that you will have to use a heavy overcoat and not gelcoat because gel coat does not like epoxy despite what WEST says. WEST=Wood Epoxy Saturation Technique. Does not say fiberglass saturation, but damn WEST does have a great marketing department!

Merlin Clark · Feb 25, 2014

Sorry I've never had a failure (in 20 odd years of my own repairs) nor have I heard of anyone professional in our area when using epoxy.
Of course it would be coated and I'll believe West, they're pretty good at what they do.

hawk232 · Feb 25, 2014

don't overlook vinylester. better adhesive properties than poly yet it can be painted with just about anything (unlike epoxy which requires ONLY epoxy to be used over that area forever). its also stronger than poly and provides a slightly longer kick time than poly (still not as long as epoxy though)