Ebiso

I've got some Salicylic Acid powder that I want to use to make a 15% face peel. I've got some Propylene Glycol to dissolve in, ( or possibly could use Isopropanol alcohol) I read I would need to use a ratio of 1:7 SA to PG. Once it's dissolved I assume I then need to dilute it with water? what is the process for all of this, how do I work out the percentage strength of the SA? I've been looking around the web but can't seem to find what I'm looking for and don't want to burn my face off! any help would be appreciated!