@s g So what is your exact procedure with cuttings? You stick the cutting into the dry pumice sand and wait for roots? If you are watering how often? If I water pumice sand it becomes a water-logged mush, so I would worry about root rot.

I lightly water it about once a week. Just stick the cuttings into it. The sandy pumice is not dusty but of a gritty texture. I don't know what a #12 mesh means.

@s g A #12 mesh filters out any particle smaller than 1.68 mm. That is about 0.0661 inches, roughly 1/15th of an inch. The particles that get through that filter include ultra-fine dust.

I would suggest using the whole mix, not just what passes a #12 screen. i think it makes a more porous mix. But it is a potting soil for all my plants, especially cactus. i mix it 3:1 with compost for my succulents.

@Rob Blomquist I was filtering Dry Stall, and the sand I am filtering out would make a pretty slushy mix in the quantities I am finding it. Particle sizes below 1.5 mm are generally a no-no in container mixes because the surface area of the combined small particles in the container is too large and creates too much adhesion and cohesion of water in the mix. Mixing that with 25% compost in the mix would be an even bigger problem because compost also has small particles.

If your application is a raised bed with connection to the ground, that might work but did you know that in most texts of soil management for agriculture the compost levels in fertile soils rarely go above 7% to 10%? 25% compost is massive overkill.