Best primers to prevent tannin bleed on cedar and redwood?

[Downaski]

Hi!

What’s the best way to prevent tannin bleed when painting over wood like cedar or redwood? Even with a primer, stains sometimes show through after a while. Are there specific primers or techniques that work best for long-term results?

[FatimaandAhmed]

Hi! Tannin bleed can definitely be frustrating, especially with cedar and redwood. The best way to prevent it is to use a high-quality stain-blocking primer. Shellac-based primers (like Zinsser B-I-N) are excellent because they completely seal the wood and dry fast. Oil-based primers also work well, though they take longer to cure. If you're using a water-based primer, make sure it’s specifically designed for tannin blocking.

A few tips for long-term results:

• Ensure the wood is completely dry before priming since moisture can draw out tannins.
• Apply two coats of primer, letting each coat dry fully.
• Use a high-quality exterior paint if it’s for outdoor surfaces.

[Downaski]

Thanks! Heard that shellac-based primers work well, but do they have a strong odor? Also, if the cedar is already painted, is priming still necessary, or would a good cleaning be enough?

[FatimaandAhmed]

Yes, shellac-based primers like Zinsser B-I-N are very effective at blocking tannin bleed, but they do have a strong odor, so proper ventilation is important when using them. If you’re sensitive to fumes, an oil-based primer is a good alternative, though it takes longer to dry.

If the cedar is already painted and there’s no sign of tannin bleed, priming may not be necessary. A thorough cleaning to remove dirt and chalky residue, followed by light sanding to improve adhesion, should be enough before repainting. However, if you see existing stains or peeling paint, spot-priming those areas with a stain-blocking primer will help prevent future bleed-through.

[Downaski]

If I want to avoid the strong odor of a shellac-based primer, would an oil-based one be just as effective at blocking tannins, or is there a trade-off?

[FatimaandAhmed]

Oil-based primers can definitely block tannins, but they’re usually not quite as effective as shellac-based ones, especially on woods like cedar and redwood. The trade-off is that oil-based primers take longer to dry and may still allow some bleed-through over time. If odor is a big concern, though, they’re a good middle-ground option. Just make sure to apply multiple coats if needed and give them plenty of drying time!

[Downaski]

Got it, that’s really helpful! I hadn’t thought about the trade-off between effectiveness and drying time. Also, what if the wood is already old and weathered? Does that reduce the risk of tannin bleed, or can it still happen just as much?

[FatimaandAhmed]

Yes, tannin bleed can still happen even with old and weathered wood, though the risk may be slightly lower if the surface has already leached out some tannins over time. However, aging also makes the wood more porous, which can allow moisture to penetrate and draw out any remaining tannins. To reduce the chances of bleed-through, it’s best to start by thoroughly cleaning the wood with a mild detergent or wood cleaner to remove dirt, grime, and any chalky residue. Light sanding can also help smooth out the surface and remove any loose or oxidized fibers. Even if the wood looks stable, applying a good tannin-blocking primer, especially for cedar or redwood, is a smart precaution. If you don’t see any previous stains and the existing paint is holding up well, you might get away with just using a high-quality exterior paint, but priming is still the best way to ensure long-term results without unexpected staining.

[Downaski]

I really appreciate all the helpful details. Thanks so much for taking the time to explain everything!