I've molded a few composite inductor cores of JBWeld (5% Ferrosilicon "steel" Filler). Can highly recommended for energy storage or flyback choke only, not for motor. Too much reluctance from too much distributed gap. Only conducts flux 3~6x better than air, which might be enough to guide the field out of (and not setting up eddy currents in) your wire. Its certainly suitable for gluing up blocks of ferrite or other sintered powders. Or when you don't want flux to mushroom as it crosses an unfilled gap. Or don't want a gap to be mechanically unsupported. I just shave a sliver to 3x the calculated air gap and glue it in, problem solved.
Now you can fill JB much further than 5% (with crushed material) to carry more flux. But even solid ferrite only carries about 1/3 the flux of iron. Its going to make for a very weak motor, unless perhaps you build for high RPM instead of high torque. Epoxy will
block eddies bigger than any conductive iron particles suspended in it, so long as they aren't packed so tight they touch. Plenty of magnetic materials, like ferrite, are near electrical insulators anyway.
So, lets talk about ferrite for moment. What it is and isn't. Its a crushed and sintered artificial gemstone. Made of Iron Oxide and Zinc Oxide. The iron is always a hard magnet, hard as in permanent like the back of a loudspeaker. Takes a lot of energy (high remnance) to flip from one pole to the other. For soft forgetful magnets (low remnance) like flyback transformers: Manganese Oxide and/or Nickle Oxide are added. I don't have a clue what the Zinc does, maybe its mechanical...
Manganese isn't magnetic by itself, and nickle just barely is. But put them in crystal with iron and they seem to pick up a clue about how to act like iron does, except they forget more easily than iron. But you have to operate below the threshold where disordered iron begins to get involved, or it starts to organize into domains, and then its ruined. Becomes lossy ferrite like you might see for a suppressor bead. Disorder can only be restored by putting in an oven, regular "demagnetizing" won't restore the required small scale disorder to the iron, only create a balance of ordered domains which isn't the same. Manganese knows and cares the difference.
So anyways, I ruined my first composite core by doing everything wrong, not knowing any better. I smashed up a bunch of supressor type ferrite beads, which makes a bunch of dangerous sharp and insoluble powder you do NOT want to breathe. Then inverted a ziplock bag over my hand (holding a neodymium in my fingers) to mop up the powder. Flipped the bag closed and man, I was a genius! WRONG...
1st mistake: Supressor ferrite. 2nd mistake: striking ferrite, unshielded from Earth's field. 3rd Mistake: picking up with Neodymium. I could have fixed all that in a sufficiently hot oven, or maybe a microwave. But didn't know I needed to, until after was already molded into an Epoxy that now wouldn't survive the Curie temperature. Had to start over, but eventually wound a racetrack core in Litz, good to 1MHz.
Want to make a boost converter for your bike? Maybe epoxy with ferrite filler is good stuff. Motor you are wasting time unless you got a plan way outside the usual box. I got no clues but absolutely silly RPM how you might approach that.