The other problem I have had with FINE dust, like from a sander collection bag,
is that you need to not put it on there in big lumps. they just turn anaerobic
at get nasty and slimy. I usually tried to sprinkle them in along with the
layers of manure, and sort of scratch them in with a rake or fork or something
to break them up.
And, they are right. watch out for the preserved stuff. Some have some pretty
nasty organic poisons in there like Penta, others use metal salts, and in a lot
of cases even arsenic.