The material is a gooey, non-sticky mix. (Think silly-putty like.) In the mix are tiny balls (nano particles) that have a reagent inside. The shell of the balls decomposes in the presence of an electric field. Then, the reagent is released, which causes the mix to harden into a stiff material.
Now, add to this, if you're hand sculpting skills are not good enough for the task... custom fold-out wire frames. This would make for nearly instant, cheap (extremely low material usage) assembly, in the field of:
1) Custom temporary replacement parts for broken down cars, motorcycles, bicycles.
2) splints, protective pads
2) Knives, throwing stars, etc... (just bring some sandpaper)
3) toys
4) patching holes in pipes or walls.
5) copying keys
6) replacing broken wheels or handles on luggage, etc...-- sophocles, Jun 19 2009 Influence of an electric field on epoxy hardening http://www.springer...t/a474u25w47164130/A place to start. [csea, Jun 20 2009] epoxy putty http://www.aplusbputty.com/epoxy.htmfor e.g. [afinehowdoyoudo, Jun 25 2009] I will neutralize the neg vote with a positive, just for intent.-- blissmiss, Jun 20 2009 Great concept; I have wished for a substance like this now and then. I like that you've considered a mechanism for activation, but am not convinced that the core is not WIBNI.
Also, even if such a substance existed, it might be a bit hard to apply/control the electric field if the item being patched/fixed, etc. were electrically conductive itself.
How about doing a bit of searching on electric field or other possible activation metods? Here's a [link] to get you started...-- csea, Jun 20 2009 I didn't want to bog down the core idea with such details to make it less readable... but here goes....
Activation could be through many other means too. Maybe the spheres are made out of microscopic interlocked magnetic blocks. (Water is slightly polar and other molecules as well. It just takes smarts to assemble these. Think "weak ice", and go from there with other polar materials.)
Then, a high frequency magentic field (switching back & forth) would penetrate the material and break the interlocks, releasing the internals. Such a field would be easy to do with a 9V battery, and an oscillator, which is in nearly every wristwatch. It's again, just rather straightforward engineering with existing modules, which is no stretch for HB'ers.-- sophocles, Jun 21 2009 random, halfbakery