Dry stall doesn't even compare to pumice. Dry Stall will break down, pumice won't. Pumice holds way more moisture and nutrients than drystall.
Pumice and lava are both volcanic byproducts. Pumice is much lighter and less porous than lava is and is only available in a white/grayish color.
Lava is heavier by nature and is more porous than what pumice is. Lava comes in many sizes and I find what works best for me on large and small trees alike is the 3/8" size. Lava won't break down either and can be reused like pumice if you choose to.
The best roots I have ever seen is with unsifted pumice. 100% pumice will create roots like nothing you have seen before. Doesn't matter if it is a trident, RMJ, Ponderosa, Hornbeam, Linden, etc..... the fine feeder root growth will be out of this world.
Sounds to me like I should start importing it back east...... LOL!!!!
Jason