Getting a smooth finish from styrefoam mold

Anyone out there have either a product or an idea that I could smooth the machined imperfection out of a shaped piece of styrefoam.I am intending to fill the surface, sand,pva, gelcoat and glass it without melting the foam .Thanx, Bob

epoxy resin thickened with phenolic micro-balloons. Polyester (vinylester, etc.) resin will dissolve the Styrofoam but you should be safe with epoxy.

Watcha' makin'

I second the epoxy. You can't use polyester on Styrofoam.
Are you using expanded Poly? If so why not use the blue (or pink) extruded, it shapes better and can be glued together to form big blocks.

So, what are you building.
And send pictures!

If this is a mold, and the foam is going to be removed before you use the molded part, you could try a thick even coat of "setting type" drywall joint compound. It is the type that comes in a powder form and sets in a specific amount of time...the 45 min works as a good all around time frame...they make 10 minute and 15 min but unless you are doing a really small area it will set up way too fast.

You can get a smooth surface...definitely need to have plenty of release agent on it though as resin will bond tightly to it. The down side is that if you get even a small hole in it...or you sand it too thin polyester will melt the Styrofoam under it in a heart beat.

If the foam is going to be left in place I would go with the Epoxy/glass bubbles "bog".

I found a CNC nearby and, as a consequence, would be interested to learn about building techniques based on CNC cut styrofoam. Any website indication or recommendation is welcome.

Anyone tried to CNC cut an entire styrofoam hull plug, epoxi/glass the outside and then dissolve the styrofoam with a solvent? Do you think it would work?

Thanks,
Luiz

Leave the foam inside the hull: unsinkable boat

I think the right way to proceed would be to make two half hull plugs, build molds around those, and then build hulls from the molds.

This said I've seen recently a web site from a Acat build who made his carbon hulls directly from CNC plugs. Can't find it at the moment however...

You might mean this site http://a-class.org.nz/daryl.htm

"Anyone tried to CNC cut an entire Styrofoam hull plug, epoxy/glass the outside and then dissolve the Styrofoam with a solvent? Do you think it would work?"

I did it with a 12' kayak...shaped a Styrofoam hull and glassed it then mechanically removed the core with the help of a HD Shop Vac. Dissolving it was too messy in my minds view. Originally I was going to leave the core in but with a shape of any real volume the core is too heavy.

That's the one! Thanks.

what is the melting point of styrofoam? is it lower than the cure temperature of an autoclave epoxy?

A builder in Brazil told me that he did the same, only used a solvent to dissolve the styrofoam. I don't remember what it was, though.

"A builder in Brazil told me that he did the same, only used a solvent to dissolve the styrofoam. I don't remember what it was, though."
Just about any solvent except Alcohol will desolve it...Gasoline, Laquer Thinner, Acetone, Toluene, Mineral Spirits... I would test to see which one does it with the least clean up problems and one that is less flamable/explosive. I am glad I scrapped mine out...it was very clean and I didn't have to deal with a bucket full of toxic waste.
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You shouldn't leave styrofoam in a hull anyway, it soaks up lots of water, increasing the weight of you boat over time.

http://www.quickform.net.au/
http://www.mouldcam.com/index.php

There's a similar company on the Gold Coast, can't remember name, that produce their moulds with a rough, deep cut into styrofoam then cover that with a thick epoxy filler for final cut, then paint and polish.

Here's the filler, on first page.
http://www.atlcomposites.com.au/files/news.news_2009/newsletter_12_-_autumn_09.pdf

Who out there does custom CNC plug-cutting? I know someone who's interested in getting some made and is looking for a source.

Where are you located?...Remember this forum is world wide...

Thanks for the tips so far. this project involves indoor waterslides.The styrefoam being cut by a cam machine out of 4x6 ft. blocks .I already tried Interlux 2000e/2001e two part epoxy bottom primer and vc17 two part bottom paint as a sealer filler but they both eat the foam in minutes.As suggested I am waiting for some gypsum plaster to dry to sand then wax pva and finally gel in an assortment of colours.I also thought of draping or heat shrinking some plastic over the foam to remove the pits . This is all about getting that smooth waterslide finish.

The local source is http://www.dreamperformance.com. Certainly too far for your project, though.

Great information, thanks!

This just showed up on sailkarma.com, I thought that this boat was made from carbon and honeycomb!



Don't you just hate it when the bow falls off.

It was - but they just recently scabbed on beefier bow sections...but I too thought even those pieces were carbon honeycomb. Ouch...back to the workshop.

Hopefully they towed it out of the environment...

http://www.youtube.com/watch?v=8-QNAwUdHUQ

I shouldn't make jokes, same thing happened to my boat.

I love that skit.

+1. Best one I've seen. Always makes me laugh.

Thats was great!

Thanx all,as it turns out the West Epoxy seems to be working out so far. Bob.