[markkanof]

There are a bunch of different products under the JB Weld brand that are two part clay like material. They are designed for things like patching wood, patching metal, etc. The two parts are different colors, so you take the two parts, squish them together, and knead them a bit until they have a uniform color and then you can mold them into whatever shape you need. I've used the wood one quite a bit for repairing small rotted sections of wood and it works well. Not sure what the shelf life is, but in it's two part state I've had containers around for over a year and they seem like new.

[xenomachina]

I've used two part putties that should like what you're describing, though I think the ones I'd used weren't JB Weld brand. I'm pretty sure they were all epoxies as well.

When the JB Weld putties you're talking about cure are they hard and brittle, or flexible and squishy? The ones I'd used all cured to a hard plastic.