Drywall, Paint and Preservation and Suspended Ceilings Seabee BU A School Practice Exam

The idea here is using a barrier layer that both binds and seals the wood so that anything inside the knots can’t migrate into the finish. Shellac does that very well because it’s a natural resin dissolved in alcohol that forms a hard, adherent film when it dries. As a binder in varnishes, paints, and stains, it provides reliable film formation, and when you apply a coat over knots, the shellac seals in the knot’s oils and resins, blocking them from bleeding into subsequent coats. This quick-drying, easily-sanded sealer creates a stable, compatible surface for the next finishes, which is why it’s widely used for knot sealing. Other finishes can topcoat nicely, but they don’t inherently provide the same effective knot sealing action that shellac offers.