On p. 39, TOH, March, 2009, para.3, "He (John Thomas) shuns polyurethanes, which get so hard that they can pull off the underlying shellac."
What is "pulling off". What will it look like, this pulling off the underlying shellac? Is this a chemical reaction?
Can someone explain this?
I have been using thined shellac as sealer before applying polyurethane on heavily used oak steps. It looks fine. Can I expect some kind of "pulling off" now? What will I see?