Castain T40 – Tannin-Stain Blocking Additive for Wood & Coating Systems

Castain T40 from CAS Additives is a high-performance anti-tannin additive developed for wood-coating formulations, especially where tannin bleed-through is a challenge. casadditives.com Tannins – naturally occurring poly-phenolic compounds in woods such as oak, cedar, redwood – can migrate through primer and topcoat layers, resulting in unsightly stains, discoloration and compromised coating integrity.

Utilising an effective chelating mechanism, Castain T40 neutralizes soluble tannin molecules and prevents their migration to the surface of the coating. This enhanced stain-blocking ability also improves resistance to high humidity and yellow-stain development. The additive is compatible with water-based and solvent-based wood coatings and helps formulators deliver clear, durable, stain-free finishes on tannin-rich substrates.

By incorporating Castain T40 into primer or topcoat formulations, manufacturers achieve cleaner surfaces, fewer rejects, and improved perceived quality of finished wood coatings—all while reducing the need for heavy pigment loads or costly rework.