You only get about a 15 to 20 minute window to work it before it starts to set (depending on how much catalyst you use). I suppose you could use it o the outside of something if it's only a mass of material you're looking to shape but it might be difficult to see what's what as it is transparent. It might be easier to use filler as it is opaque and would be easier to see what you were doing but it all kind of depends what it is you're trying to achieve I suppose. Two part epoxy putty is also a nice material to work with depending on the purpose. I'd be amazed if amongst those three things you couldn't find something that would work out.