Water-based Stain-blocking Primer/Sealer

Stain-blocking primers are used on wood that has high tannin content which can bleed out and cause stains. This CP considers stain-blocking primers that can be used on multiple additional substrates including drywall. Stain-blocking primers can be oil- or water-based. Water-based stain blocking primers are typically designed to lock the stain in the primer coat, while solvent based primers are designed to block the stain completely. Stain blocking primers may be advertised for interior and/or exterior uses. This CP considered water-based stain-blocking primers for interior/exterior use. Self-priming paints with stain-blocking properties were excluded. The composition of water-based stain-blocking primers is similar to that of a wall finish paint with some notable exceptions. Historically alkylphenol ethoxylates (APEs) have been used as surfactants in acrylic paints and primers. This group of chemicals includes nonylphenol ethoxylates (NPEs) and octylphenol ethoxylates (OPEs). NPEs, OPEs, and their breakdown products have all been shown to have endocrine disrupting properties. While wall finish paints have been shifting away from the use of APEs, they were the most common surfactants identified in stain-blocking primers. In addition, stain-blocking primers and sealers typically contain an antistain additive and a corrosion inhibitor. They may also have higher VOC content than wall finish paints. Most products considered for this CP met the South Coast Air Quality Management District (SCAQMD) threshold for low-VOC primers (<100 g/L). VOC content across all products considered ranged from <200 g/L to 3 g/L.