Its called a hopper gun and you use a small compressor with low psi to shoot it. Large chips dont work well with it. For a one time thing it doesnt make sense.
Best way to get good coverage is to roll epoxy on the wall, wait till it stops sagging and tacks up a bit, then throw the chips onto it very hard. Then use a dry roller and roll over it lightly to basically pack it on tight.
The next day use a rubbing stone to smooth it out, then seal it.