Can poly resin be used over west system epoxy?
 

I just acquired a 1970/71 20sf from my friend! My brother and I are going to begin the rebuild process and it is our first time with any major fiberglass project. We are trying to decide on what resin to use. Looking for any suggestions. We were ready to buy poly however i was told the transom has already been re-cored with marine ply and WEST SYSTEM EPOXY....
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Now, my understanding is that you can use epoxy over poly and vinyl but can NEVER use poly and vinyl over epoxy...

Should we continue and use west system for the entire project or do we have any other options?

Sounds like we might not have a choice...Thanks for your help.

I thought you could use vinylester over epoxy but I could be wrong.

Best bet is to stick with epoxy over epoxy, but that doesn’t mean everything needs to be done with epoxy. For example, you could use poly or to laminate your cockpit sole, and then bond it in place with epoxy.

Polyester doesn't bond well to epoxy. You can peel polyester-wetted fiberglass off of epoxy by hand. If you Google "System 3 Epoxy", they have a free downloadable handbook on their website that'll be very helpful in describing how to finish the transom, tie it into the stringers, build a deck, etc.

You can make individual parts with polyester and then use epoxy to bond it to the hull. For instance, you can use polyester to add fiberglass skins to foam core, then use epoxy to fiberglass those pieces to the hull. On a boat that size, you probably won't use enough resin to save much by mixing types.

You also don't have to stick with West System. The biggest advantage it has over other epoxies is mostly in it's ability to lighten your wallet. Once the epoxy is cured (a few days), you'll only be mechanically bonding to the existing work, so it doesn't matter if you change to Raka, System 3, etc.

"You also don't have to stick with West System. The biggest advantage it has over other epoxies is mostly in it's ability to lighten your wallet"

How true!! Quickly lighten.......

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i use system 3...but i'd go with whatever you see cheaper from everyone's recommendations here- System 3, Raka , etc. When my System3 runs out, I'm thinking of switching to Raka.

https://www.systemthree.com/blogs/ep...-the-chemistry

i would not epoxy over poly or vinyl myself. per blog which is a good read explains why. but if do must take steps.. basically check with the mnfr and see what they say?

I just spot checked vinyl seems pricey, close enough to epoxy, go epoxy. My vinyl experience was so so, real quirky temps and mixing vs epoxy for me. plus stink. Also as I recall if using CSM, ask and research been told generally no with epoxy.

Thanks for the insight! I'm leaning towards the system three from Merton's in MA, had a friend recommend them....Might as well use all epoxy for the this project to keep it simple.

I buy all my poly, vinyl and glass from Mertons. He’s a great guy with good pricing. But for epoxy I would go with US Composites or E-bond. Both have much better pricing and it’s good epoxy.

Check out RAKA as well. Wets out like a dream

Call Joel Shine at Gulfstream Composites. He sells Raka epoxy and it works great and is way more affordable than West System

I prefer Raka over System 3. I had problems in past with System 3 crystalizing. They told me to heat it. This never happened with Raka or WEST.

Raka's prices are very competitive . Joel has a lot of 1st hand experience and is very helpful so I prefer to support him.

Vinylester is used as a barrier between epoxy and polyester gel coat. The vinylester epoxy that Mertons sells has better mechanical properties than West system has. Vinylester epoxy is an epoxy that cures in the way that we associate with polyester. Both have the styrene monomer stink. Like polyester, you can tune the cure rate with MEKP.