- Q. How can pine resins be sealed to stop bleed-through on exterior siding?
A.Shellac has always been considered the sealer of choice for pine resins, but it is not considered appropriate for exterior use. However, if the shellac is thinned substantially, about one part shellac to four parts alcohol, it may work. The primary problem with exterior use of shellac is its brittleness, which should be reduced by thinning.