Q: It is my impression that shellac is the universal sealer and can be applied over anything and will bond with it, and anything can be applied on top of it, and they will bond. Is this true?

Michael Dresdner: Almost. Only dewaxed shellac fits that description. Natural shellac, which contains about five percent wax, does not. The easiest way to buy dewaxed shellac is ready-mixed in the form of Zinsser SealCoat".