Use styrofoam cooler as mold for box seat

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Jan 28, 2012
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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!
 
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Oct 22, 2007
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If it were me I'd do a 'sandwich' of glass / styrofoam / glass, it'll be very strong and light. Epoxy resin ought to adhere very well to the styrofoam, especially if you rough it up with sandpaper first. I'd probably use 2 plies on each side of the styrofoam of something like DB170 biax.

I've used the 635 epoxy sold by US Composites and have had good luck with it in boating applications.

The proper foam to use would be something like this from Wicks Aircraft: http://aircraftproducts.wicksaircraf...ams/styrofoam? but for something as benign as a seat I'd guess a styrofoam cooler should work ok. If nothing else do a small layup first and test for good adhesion on a scrap of styrofoam. Let the test layup cure for a day or so then see how hard it is to pull the glass off, if it comes right off without a bunch of styrofoam coming with it then it doesn't have enough adhesion to work.
 
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I can totally do that, thanks for the suggestion. Question. Do I create the pieces of the box individually and then glass and epoxy the corners to get it to come together?
 

moosehead

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You're fine with the styro cooler as a male mold, if the shape and dimension work for your craft then it's perfect. Latex paint or even duct tape can be used on the styro mold prior to laying the resin/glass so the mold can be broken out easily, a barrier can prevent any aggressive resin from attacking the styro as well.
 
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I can totally do that, thanks for the suggestion. Question. Do I create the pieces of the box individually and then glass and epoxy the corners to get it to come together?



Do whatever it takes to get the shape you want. You can make individual pieces first and then put them together with a couple plies of glass (top and bottom) overlapping a few inches on each part (scuff up the cured glass with sandpaper and then clean it first), or else you can form the entire part and do it all at once. It's just a matter of figuring out which will be easier for you. My guess is that it would be easier to make individual parts and then glass them together, but if you can do it all at once you've saved yourself a step.
 

robert graham

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Why not just buy and use a cooler that's the right size and shape?....then you can open it and use it for storage of PFD's, ropes, anchors, etc.....
 

kjdunne

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I've used 2 - 96 qt. Igloo coolers as seats / storage for years in my Tracker V-17 fishing boat. When I replaced the decking, I reinstalled the original pedestal seat in the raised bow deck only. They work fine, I use 1 for ice / fish box, the other is dry storage. Tie down kits and cushions are readily available. Just pick the size that works best for you. Only downside, no backrest.
 
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Couple reasons, mainly because I want to work with Fiberglass and Epoxy to see if its something I enjoy enough to build a stitch and glue skiff. The other reason is that I may add a baitwell as part of the box with two hinged "seats" one for the cooler/storage and the other for the livewell. To start I'm going to just get the box form in place and then possibly glass in a livewell at one end if it goes smoothly and if I want to proceed. Unless...there is a 32" cooler that features a recycling 3 or 5 gallon baitwell but I doubt it.
 

smokeonthewater

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Here is MY take on the project.... cut several slots in the cooler about 1/4 x 2"... get a roll of 6 or 8" glass cloth tape... cut several @4" lengths of said tape, soak in epoxy and thread em in an "S" through the slots stuck to both inside and outside of cooler...... This will solidly tie inner and outer together

Next glass both the inside and outside... epoxy WILL bond perfectly with styro...

when you are done you will have SOLID glass box that is light weight and very strong...
 
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Sounds good...the cooler options I have are 1" to 1.5" thickness, what type fiberglass and how many layers do you think are necessary? The LxWxD is 29x15x12. I' want to try to get it to as close as a gel-coat mold type finish. Thanks again!
 
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Sounds good...the cooler options I have are 1" to 1.5" thickness, what type fiberglass and how many layers do you think are necessary? The LxWxD is 29x15x12. I' want to try to get it to as close as a gel-coat mold type finish. Thanks again!



If it were me I'd do a 'sandwich' of glass / styrofoam / glass, it'll be very strong and light. Epoxy resin ought to adhere very well to the styrofoam, especially if you rough it up with sandpaper first. I'd probably use 2 plies on each side of the styrofoam of something like DB170 biax.

I've used the 635 epoxy sold by US Composites and have had good luck with it in boating applications.


Visit the US Composites website - *****************.

I' want to try to get it to as close as a gel-coat mold type finish.

That'll take a filling compound, you can use the 'SM Fairing Compound' found on this page:

http://*****************/fillers.html

You mix it with epoxy resin to a consistency of something like peanut butter, spread it on like bondo, let it cure and then sand.


edit: OK, I see that this website isn't allowing me to post links (I bet it allows links to iboats products :mad-new: ). Go to uscomposites dot com and search for "SM Fairing Compound"
 
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I found the DB 170, that is the best price for glass and epoxy on the net I think. I read that the DB 170 with Mat provides bulk but offers no more strength? Is this true and if so should I get the no mat since I only want it for strengthening the walls to sit on?
 

jbcurt00

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edit: OK, I see that this website isn't allowing me to post links (I bet it allows links to iboats products :mad-new:
As it should be, don't ya think? Do you post ads/links for your company's competitors on your company's website?

Iboats sells poly/epoxy resin and fiberglass mat/cloth, so look thru their offerings too
 

Bob_VT

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Okay this is a Building question and in the wrong area ...... moving to restoration area.
 

sphelps

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If you plan on using gellcoat for a finish then epoxy would not be the type resin to use ..If your gunna paint it then epoxy will work great ..
 

undone

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The typical way to make a custom shape cooler is to buy some sheet foam of whatever thickness you feel will work for your project (thicker keeps ice longer but takes up valuable space), cut the sheets to size and then hot-glue them together, this lets you glass the entire thing as one piece, it's much easier than individual panels. Use a good gasket for the lid and it will work very well.

Fairing the outside to be smooth takes some time, the filling and sanding just doesn't go fast.
 
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I like the idea of using a cooler because the edges are rounded inside and out and the walls are 1.5" thick. What is the easiest to use to fair out the outside to make smooth?
 
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