Many people use it as a substitute for Turface in what everyone refers to as 'the gritty mix', which is what I use for bonsai soil. It's pH neutral and holds more water than Turface, so it holds a lot more water than pumice. I'd be sure to screen it over insect screen to remove the fines, and I'd screen the PB to >1/8 but If you want a suggestion for a starting point, I'm thinking

3 screened bark
2-3 screened #8822
4 screened lava

should work well if the lava is close in size to the #8822. Remember your soil is essentially devoid of nutrients, so ensuring your plants get all the essential elements plants normally get from the soil IS essential. Sorry if you knew all this. If so, maybe others will gain from the conversation.

Al

Thanks Al.

Always look forward for your help.

Paul