The ashes work excellent and in my use they seem to bind well to the ice. The problem for me is that I have lots of nails from the ashes, and the tires seem to find them.Ive been desperate a couple times and used the ashes on the tire footprint portion, and then walked along and picked the nails out and also a magnet but its easy to miss them and always seem that it only takes one.
But if no nails it works great ,at least on a gravel drive not sure on paved if in the spring it would be another clean up chore or not.
As for the sand I use, I get a load of sandy fill each year and , wait for a day when its been hot and dry, and then shovel it into a 50 gallon drum and place in the basement , then its dry to use in the winter, (I just use it with a shovel)
Id think the key would be for it to be as dry as possible to drop down the sides of the then spreader.
Hope this helps.and nice set up Hammy.