Big pieces of foam/polystyrene

By arjaytistic. 07/07/12, 10:32 pm

Let's say I was making a canoe by spraying fiberglass onto a mould that I had shaped into a canoe shape, what would be the best material to use for the mould and where would I find it in a large size? The kayaks we are making are about 1m wide, 1.5m long and .5m high. I know I've seen big cubes of polystyrene but they tend to lose little white balls everywhere when you cut it so I'm not sure about how good it is for making a mould out of. I've also seen some videos where they use "foam" (and don't elaborate on what type of foam) that you can actually use pieces of the same foam as sandpaper on itself to rub down after hacking the general shape from it...?

-- rj xx

By Cookie Monster. 17/07/12, 03:28 pm

Don't go anywhere near polystyrene unless you're using it to pack a box.

Use Styrofoam - the "foam" you were asking about.
Best place I found to get large amounts of it from is Forman Construction (www.forman.co.nz or more specifically for Styrofoam: http://www.forman.co.nz/products.php?catid=31&proid=330).

Also a few tips you might find useful:
For cutting and shaping I recommend using a Japanese Pull-saw (http://www.classichandtools.com/acatalog/Classic_Series.html - The Douzuki 150mm Classic). It's a worthwhile investment for big projects; the pull saw only cuts on the pull stroke, so cuts in only one direction giving you a smooth cut and a smooth edge unlike a normal saw which cuts on the push and pull stokes, so it ends up shredding and tearing your styrofoam.
You will find sawing will be a lot faster, easier and give a better shape that hacking away with a knife. Then you can use sand paper from there to smooth out your shape.

If you plan on keeping your moulds, wrap the whole thing in brown packing tape first (2-3 layers): The fiberglass won't stick to it. It will be rough inside from the wrinkle of the tape, however it'll still be smooth on the outside - you can always sand the inside once you're finished.

And finally use epoxy resin - Just in case your resin seeps thought your packing tape, epoxy resin would melt the styrofaoam.