Use styrofoam cooler as mold for box seat

I'd like to build a custom box seat for my J16 skiff. I was planning on building a wood frame and thin plywood and then sealing/encapsulating in fiberglass and epoxy.

I'd like to make it weigh as little as possible so it occurred to me I might be able to use a Styrofoam cooler to get the shape I want.

Few questions:

1.) Using just fiberglass, can this be made strong enough and if so, what type of fiberglass should I use and how much?

2.) How do you "treat" the styrofoam so the fiberglass will "pop" out or does the styrofoam not adhere to the fiberglass/epoxy?

3.) As another option, should I just use at least a 1X2 wood frame and sytrofoam sides to shape the sides in fiberglass to give more strength?

Any additional advice is appreciated as my inexperience with these materials probably leave out a few questions I should ask but don't know.

Thanks!

 

Making the seat out of solid fiberglass can be done but it will be relatively heavy and costly. A core would cut weight and cost.

Styrofoam will likely not release from fiberglass and might not even be compatible with resin. Polyethylene plastic sheet is a good release.

There is foam core that is designed specifically for fiberglass work. I have seen some guys who use cheaper construction foam -ask on the build forum. The way I would do it is make a male mold out of the core, dry fit fiberglass, wet out with epoxy, then use polyethylene sheet over top to get a smooth finish.

Post dimensions for comments on fiberglass -on the build forum.

 

That would work, is there a URL or supplier for the Polyethylene sheet for purchase? I am very new to the materials you are referring. Thanks for the help.

 

All the plastic sheet I have seen in the big hardware stores has been PE and even if it is polypro or PVC it should be OK.

I am less certain about foam compatibility if not specifically designed as core. Ask the builders.

 

I found the folks at Fiberglass Supply to be very helpful when I was first getting started with fiberglass years ago. I sent them a sketch of what I was trying to build and they told me the best way to go about it.

http://www.fiberglasssupply.com/

They sell foam core material for surfboards and other projects. Many times instead of using foam as a mold material that will be removed the foam remains in the finished project (like in a surf board). If you're not already, maybe you should be thinking along those lines. Shape the seat in foam and glass both the inside and outside.