I know of NO wax that's strong enough to withstand 11000 PSI without rupturing. That's why modern shotgun wads are made of poly-plastic, or even nylon. Old paper wads are made of multi layer paper, felt, and other fibers.
Multi-wad shot columns were how shotshells were loaded for many years before the use of plastic wads became common.
www.ballisticproducts.com has many choices of paper, fiber and cork wads for constructing multi wad shot columns for specialty shells like buckshot and slugs.