It sounds like you need to develop a material that will either stay in place when deposited and slowly harden, or harden immediately upon deposition. FDM printing works because certain thermoplastics harden so quickly after being melted and extruded. A clay-like material would be an example of the former. But there's only so much weight that an unhardened "toothpaste" material will support before it starts sagging - you can try it yourself next time you're brushing your teeth.

If the material you have in mind needs a catalyst to harden, you might think about extruding both the resin and catalyst through a mixing nozzle, like the ones used to dispense epoxy: http://www.techni-tool.com/512AC441?...170411205942:s