Scoria/lavarock as a substrate

[camille1585]

AI few people here grow their orchids in scoria / lavarock, particularily Catts it seems, and it seems like an interesting substrate to test. I have 3 Catts that are/were in need of repotting, and two are already repotted in bark, and for the other I'd like to give scoria a try, but the trouble is that I don't know very much about it.

A few questions:

Is the size of the rocks important? It doesn't seem super common in stores here, so it's good to know if I need to be picky about size or not.

How does it behave compared to bark in terms of watering?

It seems that it's often used in warm climates where people need to water frequently. Are there any issues with using it in a more temperate climate (mostly indoors)?