concrete over foam

[lfry]

I have scanned other threads, but not finding quite the info I'm looking for. Looking for the latest on materials for creating a large-scale concrete sculpture by first laminating sheets of rigid foam, then carving the foam, then applying a concrete product such as Silpro FSB that has glass fibers in it already, combined with a polymer admix.
Questions:
1) What's the best kind of foam to use? What is the best glue for laminating sheets of foam?
2) Can the surface of the foam be scratched up and then the Silpro (or other product) be applied, or is it necessary to cover the foam with wire or fiberglass mesh? If so, what's the best mesh to use?
3) I have used Silpro FSB (Fiberglass Surface Bonding Cement) small-scale. Is there a better product? I've heard others mention Umaco and Quikcrete.
4)If this is to be an outdoor "permanent" sculpture, should the surface be sealed? The bottom of the sculpture would be foam, should it be covered so it is encased in concrete like the rest of the sculpture?
A lot of questions, thanks in advance!
Leslie

[Andrew Werby]

1) What's the best kind of foam to use? What is the best glue for laminating sheets of foam?

[Styrene-based foam (Styrofoam TM) is the cheapest, and you can cut it cleanly with a hot wire. (Don't try that with a urethane foam, because it generates toxic fumes.) Gluing it is tricky, since many common solvents will dissolve the foam. Weldbond might be a good choice: http://www.weldbond.com/crafts_hobbies_models ]

2) Can the surface of the foam be scratched up and then the Silpro (or other product) be applied, or is it necessary to cover the foam with wire or fiberglass mesh? If so, what's the best mesh to use?

[Look for a mesh that will conform to a compound curve. Most won't.]

3) I have used Silpro FSB (Fiberglass Surface Bonding Cement) small-scale. Is there a better product? I've heard others mention Umaco and Quikcrete.

[I haven't done this myself, but I've heard that some of the concrete patching compounds that come premixed in buckets work pretty well: http://www.thoroproducts.com/pdf_app..._thoroseal.pdf There are building systems being used a lot lately that are similar to what you're doing; here's one: http://www.styrocrete.com/ Anything you think you might use should be tested first, on a small scale, before you make a commitment to it for the big piece.]

4)If this is to be an outdoor "permanent" sculpture, should the surface be sealed?

[It probably wouldn't hurt, although natural unsealed concrete seems to hold up pretty well in most places. If you're using something with a lot of admix in it, it shouldn't be necessary, though.]

The bottom of the sculpture would be foam, should it be covered so it is encased in concrete like the rest of the sculpture?

[That sounds like a good idea. Make sure there's a way to move the thing without damaging it - putting it up on skids so a forklift can get underneath might be helpful.]


Andrew Werby
www.computersculpture.com