i sealed the backs of my splits with 3lbs shellac mix just minutes after debarking. did two coats, the shellac dries ultra fast, and nearly almost as soon as i finished the first coat, i was starting on the second coat. sealed the ends, and backs.
if the shellac will not gum up when you drag sand paper across it, then its dry enough for another coat.
looked all over for shellac, and found it finally at Lowes, made by Rustoleum, yellow can, comes in a gallon, or quart.