Stain blocking options

“Final Report on Standard Agreement No. 09-428 For the Period June 23, 2010 through January 31, 2012 Low Volatile Organic Compound (VOC) Stain Blocking Specialty Primer Coating Prepared for California Air Resources Board Raymond H. Fernando, Professor Dane R. Jones, Professor Department of Chemistry and Biochemistry California Polytechnic State University May 21, 2012”


Page 5.


B. Introduction At the time of initiation of this project (June 2010), regulations in California allowed specialty primers, sealers, and undercoaters (SPSU), also referred to as stain blocking primers, to have a VOC content of up to 350 g/L. Several air districts had plans to lower the VOC limit for this category to 100 g/L by January 2012. The best performing stain blocking primers on the market, as accepted within the industry, are shellac-based primers, with a VOC limit of 550 g/L, and several oil based primers with a VOC limit of 350 g/L. However, there have been a number of recent advancements in developing low VOC waterborne stain blocking primers (1-7). A number of recent products with less than 100 g/L VOC also have been introduced to this market by paint and coating companies in recent years. 5 Typical stains that require blocking include tannins, various household markers, and smoke and fire related stains. Tannins are naturally occurring, plant-based polyphenolic compounds that are found in all wood species (8). Knots in the wood usually contain a higher concentration of tannins and other staining agents. These staining agents can leach out of the wood and into the coating, causing significant discoloration in the case of woods like redwood and cedar. Tannins form water-soluble compounds when exposed to the basic conditions typically associated with waterborne paints. A solvent based primer usually is more effective than a water based primer at preventing migration of tannins into the topcoat; however there are ways of preventing migration using a water based primer. Tannins can be made to bind chemically in the primer so they would not migrate. The conventional approach to this method is to use a cationic polymer dispersion with a reactive pigment, such as zinc oxide and other inorganic compounds, which form complexes with tannin compounds (9). Another approach is the use of a chemical pre-treatment to remove staining agents from wood (10). This method is undesirable because it adds another costly step in coating wood and also because it could have negative effects on the physical properties of the wood.

Our discussions with industry experts led to the conclusion that there is currently no industry standard for what classifies a stain blocking primer as having “acceptable” performance. For this project, it was necessary to create a set of guidelines to determine if a stain blocking primer shows “acceptable performance”. To define “acceptable performance” and to select candidate primers for comprehensive testing, an industrial panel made up of companies and organizations having a vested interest in the project were gathered by the ARB. This panel was made up of following companies and organizations:

  • American Coatings Association
  • Akzo Nobel Company
  • Behr Process Company
  • Benjamin Moore Company
  • Byk USA Company
  • California Air Resources Board
  • Dunn-Edwards Company
  • Eliokem Company
  • Kelly Moore Company
  • Rustoleum Company
  • Sherwin Williams Company

This panel recommended fifteen stain-blocking primer coatings for testing, along with five other coatings to be used as standard primers and topcoats when needed during the course of testing. It was agreed that, when a primer coating and a top coating is needed for the purpose of preparing substrates and test panels for performance testing of the 15 stain blocking primers, paints manufactured by Dunn-Edwards Company would be used. No Dunn-Edwards paint is included in the list of 15 stain blocking primers. 6 A series of standard characterization tests such as solids content, VOC content, density, sag, leveling, viscosity, gloss, and contrast ratio, were performed on all paints selected. Following that, stain blocking tests were conducted with household markers according to ASTM D7514-09 and tannin blocking tests were conducted with cedar and redwood substrates. Other substrates such as wood panels from real fire and water damage sites, and wood panels burned under controlled conditions were also tested. Results of these evaluations, previously presented in quarterly progress reports available at an ARB website (11), are combined and presented in this final project report. ”


  1. Sullivan, C., Roberts, A., Shearon, S. Coating compositions and methods of blocking tannin migration. U.S. Patent Application Publication 2010/0047598 A1.
  2. Tarng, M.-R., Minamyer, M., Brownell, S., Pham, A., Alexendar, A., Shah, D., Nguyen, K.L., Pham, M.L., and Maxey, S., US Patent Application 2006/0030656 A1 & 2007/0221097 A1
  3. Deng, H., Deshmukh, K., Sheppard, A. Aqueous stain-blocking coating composition. U.S. Patent Application 6,485,786.
  4. Betrmieux, Isabelle, Duque, Baudouin. Stain Blocking by WB Systems: How Does it Work? Cray Valley. Centre De Recherche De L’Oise, Parc Technologique.
  5. Tsang, Ming, et al., New Waterborne Cationic Resins for Wood Primers. Cytec Industries. Presented at: The Waterborne Symposium – Advances in Sustainable Coatings Technology, Feb. 18-20, 2009.
  6. Kimerling, A.S. and Bhatia, S.R., Block copolymers as low-VOC coatings for wood: characterization and tannin bleed resistance, Progress on Organic Coatings, 51, 15-26 (2004)
  7. Brandt-Rothermel, S., “Blocking Around the Clock,” Asia Pacific Coatings Journal, 22-23, August 2010.
  8. Vernon Donegan, Jeffrey Fantozzi, Charles Jourdain, Keith Kersell, Alex Migdal, Robert Springate and James Tooley, Joint Coatings/Forest Products Committee Report.
  9. Hodges, S., Novelli, W., Thorn, A. Tannin stain inhibitor comprising and aluminate salt complexing agent. U.S. Patent Application Publication 6,533,856
  10.  Owens, E.F., Reducing Tannin Staining in Wood Plastic Composite Materials, US Patent Application 2009/0095694 A1
  11. “Low Volatile Organic Compound (VOC) Stain Blocking Specialty Primer Coating”, R. H. Fernando and D. R. Jones, Quarterly Reports of Project Sponsored by California Air Resources Board (Standard Agreement No. 09-428), available at, (broken link)

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