Summary: Oak, teak etc. hold tannins/extractives that bleed under water/solvent and yellow white/light coats. A sealer (shellac or dedicated block primer) stops bleed and is key before white/light finishing.
Mechanism
The sealer physically isolates bleed with a fast film; for high-extractive species, spot-seal first, then full coat.
Key data
- High-tannin species (oak, red woods) need a dedicated block primer/shellac isolation.
- Over-thick sealer hurts intercoat adhesion; thin even coats are best.
Scenario
| Issue | Handling |
|---|---|
| White coat yellows | Tannin bleed — seal then white |
| Grain bleed | Spot-seal high-bleed areas |
Defects & fixes
- Yellowing/blotch: tannin bleed — add block primer/shellac.
- Intercoat peel: sealer too thick or recoated past window — thin, mind window.
- Local bleed remains: heavy areas not pre-sealed — spot pre-seal.
FAQ
Why does white paint on oak yellow?
Oak tannin bleeds and oxidises under water/solvent; seal it first.
Can a normal primer replace the sealer?
Not always; dedicated block/shellac isolates bleed better.
Does water worsen bleed?
Yes — water carries tannin more, so oil-based isolation first is safer.
Ref: wood extractive blocking practice (public).
Kexin New Materials (Guangdong) Co., Ltd. · 2026-09-18