11.   Apply two coats of clear shellac, as good a stain-killer that you can get.

12.   Apply two coats to each knot before priming and finishing with latex paint.

13.   Apply a coat of a stain-killing sealer such as BIN or Kilz, then paint with two coats of a satin finish or semi-gloss enamel.

14.   Apply a coat of latex enamel undercoater and finish with an oil-based indoor-outdoor enamel.

15.   Apply coats as instructed.

16.   Apply one coat of a latex enamel undercoater and finish off with any kind of latex paint you like.

17.   Applying another coat of water-based polyurethane is unlikely to work, because of the sealer that is not binding to the original finish.

18.   Apply a prime coat of a stain-killing sealer first, then apply two coats of the paint you prefer.

19.   Apply another coat of stripper and scrub with very coarse steel wool.

20.   Apply one coat of a semitransparent stain every five years.