2 part polyurethane kits for molding

[SHARYNF]

I have a project that needs to have some balustrades made. I was wondering if anyone had experience in using the molds that typically are used for plaster/concrete and using 2 part polyurethane foam (like the material sold in spray cans for insulation)
thanks
Sharyn

 

[mstaylor]

I wouldn't use anything that expands that much, it would be too hard to contain. I am trying to think of a better material but am missing it.

 

[scenerymaker]

Finding a mold that urethane won't stick to is going be a bit of a problem. Have you considered hot wiring them out of solid blocks of EPS foam? You could make a pattern and make square cross-section shapes very easily. By mounting each piece between two centers, you could hot-wire round cross-section shapes. Life only gets difficult if you want figures carved into them.

 

[venuetech]

You might look into this web page as they may have the products or information you are looking for.
Mold Making and Casting Materials Silicone Rubber, Urethane Rubber, Liquid Plastic, Casting Resin, Lifecasting, Epoxy Resin, Rigid and Flexible Foam from Smooth-On

or you might try a PM to brianwolf http://www.controlbooth.com/members/brianwolfe.html

 

[kicknargel]

If you find something that works (or fails!) I'd be interested in the result. What source are you using for molds?

You could also find a place that will custom cut your profile out of bead foam from your CAD. I use a place in Denver that generally makes reproduction stone and plaster work. They have a 3D router and can make any shape, and can give it a hard plastic shell. I had about 8 letters 2'x3'x1' made for about $200 and another $200 for coating.

 

[erichart]

You can also try turning solid Styrofoam on a lathe—that's how our head carpenter made a whole mess of balustrades to match the existing balustrades in one of our theatres a few years back.
I would advise against using spray foam to fill a mold. It cures through contact with the air, so if it gets more than one "layer" thick, the inside never hardens. I would highly recommend looking at Smooth-On, as they have a number of products, like 2-part urethanes, that are ideal for casting and can be very lightweight and economical. If you can't find what you need through their website, you can always call them; they are very helpful and eager to deal with theatre people.

 

[Jackalope]

You can also try turning solid Styrofoam on a lathe—that's how our head carpenter made a whole mess of balustrades to match the existing balustrades in one of our theatres a few years back.

What kind of tools did he use for shaping?

 

[beachbum]

I've seen it done with 2 part foam and was told to coat the inside of the plaster mold with liquid latex and allow that to dry before adding the foam so that foam would not stick to the inside of the plaster mold. Smooth-On has always been a good material source

 

[erichart]

What kind of tools did he use for shaping?

It was before I started working there, so I'm not sure. But the few times I've attempted Styrofoam on the lathe, I got pretty good results with just Sur-forms and sandpaper. You also want to start with as round a blank as possible.

 

[scenerymaker]

What kind of tools did he use for shaping?

I don't know about him but I have used both a hot wire and a small hand-held router with a core box (round nose) bit to shape styrofoam between centers. It turns very nicely.