Using epoxy to build from a mold

New to this forum and there's a lot of information here so forgive me if this has been answered.

Other than the higher cost, is there any reason you would not want to use epoxy as the resin for constructing a hull layup out of a mold? I'm aware that gelcoat and epoxy don't really go together, but I kind of like the idea of no gelcoat and light fairing and paint instead wont have to worry about oxidation, future repairs ect.

 

Epoxy pre-preg is quite often used with molds, so I really don't understand your question. It is important to remember that required properties, fabrication methods, and materials go hand in hand. If you are fabricating hundreds of 16 foot low cost bass boats with a chopper gun and mat, high strength epoxy makes no sense. It does make sense on a s-glass and CF vacuum bagged 45 foot ULDB. Different products, different needs, different materials.

 

Most is just pure curiosity. Not looking to mass produce but hand full of 20' no frills skiffs that are built using high quality materials. Hard to exactly estimate but on a boat that size resin is aprx 20 gal , not that dramatic of a cost difference using epoxy. Just wondering what other problems, does it have to be heated to cure? Or can you just use epoxy instead of poly or vinyl ester resin in the same layup for a stronger and more water proof product

 

Epoxy is no harder to use than other resins. All the normal stuff follows...min temp, max temp, right mix, keep everything clean, etc. The only issue I've ever noticed, was poor pot selection and/or trying to make something too thick. While all mixed resins are exothermic, I personally have had more issues with epoxy...but then again most of my personal and professional experience has been with epoxy so <shrug>.

 

20 gallons of resin for a 20 foot boat seems wildly optimistic to me. To justify epoxy, you would need to be using top-shelf reinforcements, and the boat be very weight critical, and/or speed and performance critical. You are almost mandating a cored boat as well, and vacuum infusion. The common type of polyester layup works just fine for normal service requirements, and is simpler and cheaper. You can build without gelcoat, and paint after withdrawal from the mould.

 

No. But epoxy can be post cured to improve strength. I haven't read of any downsides to epoxy except higher cost and higher UV sensitivity. And you need to absolutely avoid skin contact with resin and breathing dust when sanding, you become allergic over time. And you can't spray it like PE / VE.

In a mold you can do gelcoat and epoxy will adhere to it. But spraying gelcoat on cured epoxy is not easy.

So if you're just wondering how to get started and if you can use epoxy for everything, then yes. The added costs are just not needed for everything.

What kind of mold do you have or what boat are planning to build?

Look up vacuum infusion for least amount of hassle (but more preparation and learning). For some boat designs you can also build simple moulds out of plywood or melamine chip board that require minimal fairing. Example. Same works with PE/VE infusion resin.

You'll also find lots of videos on youtube. Explore composites has lots of examples of different of material processes.

 

Thanks for all the responses and info. I know there’s definently a learning curve and seem like there’s a lot of knowledgeable people on here. Those are the kinds of things I was wondering about does the hull need a core now and the vacuum infusion, which I’m not familiar with, those things complicate and raise cost even more

If I were to build from a mold I would be building a stitch and glue with marine ply first as a plug and prior to finishing the inside, fair and paint the outside hull and make the mold from that. If building from the mold hand laying everything, I’m familiar with epoxy and gel coat but have never experimented with other resins

 

Well I'm just a newbie new to boating and just trying to learn myself. But if I were to build a "handfull of 20ft skiffs" I'd use vacuum infusion in a cheaply build mold. Foam core or not. Time is money. But there are lots of different ways.

It all depends on what you want the boat to do (statement of requirements) and what kind of boat building plans you want to use.