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lost foam method. Need a lesson !

Post your favorite modeling 'tips' and 'tricks'

Postby AntoineL » Fri Jul 16, 2004 3:25 pm

Hello

I would like to learn this method. I may try it.
I need your help guys !

Thanks

Antoine
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Postby Rcher » Fri Jul 16, 2004 3:47 pm

It can be pretty easy to to do.

The way I've done it is to take blue foam and cut it to shape. Cover it with two layers of 3 oz fiberglass and a final layer of 1/2 oz. to 1 oz fiberglass. (The last layer of fiberglass will have a smoother finish) Once cured then physically remove as much foam as you can with a knife and dremel. Then remove the rest of the foam with actetone or lacquer thinner. I know its fun to watch the foam bubble and boil and melt but it's easier to clean the melted foam out of your hull if you remove most of it first before using actetone. :p

Once you fill and sand the hull down, then you can start adding details with bondo and styrene. :) :cool:
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Postby Rcher » Fri Jul 16, 2004 4:44 pm

I probably also should point out that I use West System epoxy to laminate the fiberglass.
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Postby Crazy Ivan » Fri Jul 16, 2004 11:00 pm

Antoine,

Here are a couple more tips that have worked for me. Cut out a number of cross sections of your hull at regular intervals from thin plywood, stiff cardboard, or whatever your favorite material. Sandwich these between your layers of foam as a guide to your carving. You just sand down until you see the edge of the sections. You can use drywall compound to fill in any uneven areas to get a smooth finish. The idea is to get your foam plug as close as possible to your final shape, minus of course the anticipated thickness of your glass laminate. Then you do not want to apply your resin to thickly. This will avoid a lot of final sanding. Also, it helps to mount your foam sandwich on a central rigid rod to keep everything in alignment.
If you plan to use polyester resin rather than epoxy, you can coat the foam plug with several coats of clear polyurethane. This keeps the resin from melting the foam, which it would otherwise do. You can follow the polyurethane with several alternate coats of Poly Vinyl Alcohol (PVA) and liquid wax to form a mold release. Then you can just pop the plug away from your finished piece rather than melting it with acetone. This is handy for items like conning towers, etc. where the finished piece can be lifted off the plug. You can then reuse the plug. Experiment.
Good luck.
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Postby AntoineL » Sat Jul 17, 2004 5:19 am

thanks guys !

antoine
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Postby Sub culture » Sat Jul 17, 2004 7:02 am

If you use polyurethane foam instead of polystyene, you don't need to worry about using a barrier when moulding with polyester resin.

Polyurethane foam is the stuff used for insulation (yellow in colour). If you go round to your local builders merchants, you'll probably get enough broken bits to build the plug for free.

Caveat, sanding this stuff makes your hands itch- use gloves!

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Postby boatbuilder1 » Mon Jul 26, 2004 9:07 pm

heres a trick I found that works and its cheap get your shape down to where you want it then paint it with three layers of household indoor outdoor latex enamel this a pretty good barrier for the resin make sure you use a respirator and gloves when sanding the foam and GRP

please
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