Is the permeability of normal shellac (flakes dissolved in spirits) the same as Zinsser B-I-N sealer?
I cannot answer this question but can tell you what we did to get the answers we needed.  We emailed (or you could call for) the specific questions we needed answered to the manufacturer of the Shellac product...Zinsser, by Rust-Oleum.  They responded in a couple of days and were very helpful.