Home > How To > Foundations > Q&A: Rx for Bleeding Knots Foundations Q&A: Rx for Bleeding Knots Sizing a Steam Boiler By Hank Spies Login or Register to download the PDF version of this article. (167.8 kB) A. Two coats of primer and two coats of finish paint should do the job. The sealers used for interior surfaces, such as pigmented shellac, will cause premature paint failure on the exterior. Login or Register to read the full article.