Picture this: let’s say that there’s a painter and said painter has a job lined up that they’ve been pretty excited about. What the paint job entails - who they’re doing it for and what they’re painting doesn’t matter - just imagine them taking their time to paint their beautiful wooden whatever, only to have blotchy brownish/tan stains start to appear on the surface they just painted over.

It doesn’t matter how many coats of paint they apply to the wood either. Those weird, mysterious stains aren’t going anywhere and suddenly the painter’s hard work becomes a smoldering heap. What our imaginary painter has just experienced is tannin bleed and it’s a pretty common occurrence. Needless to say, today’s article focuses on how to keep it from happening.

What Are Tannins and How Does Tannin Bleed Happen?
Tannins are a kind of complex chemical that can be found in many different plants, including trees - more specifically the bark and wood. Tannins inside of tree bark help to protect the tree from fungal and bacterial attacks. Tannins can be used to treat several ailments like tonsillitis, skin eruptions, and can be used as antidotes for glycosidic and metallic poisons.

Despite the ostensibly beneficial uses for tannins, the substance can be a nightmare for painters due to the dreaded tannin bleed. Tannin bleeding can happen with every type of wood but redwood, mahogany, and cedar are particularly prone to staining in this manner. As for what causes it, tannins are either water or solvent-extractive (they absorb water or metals), with most kinds of tannins being the former.

As it turns out, latex-based paints aren’t very tannin-stain resistant. This means that applying latex paint directly to wood of this type can result in tannin bleed due to its high water content. That is to, say the wood soaks up the water in the latex paint and this helps draw out the tannins.

Tannin bleed can also occur if there’s a lot of moisture inside of the wood’s surface. Typically, in these instances, the staining will occur a while after the paint job has been completed. The water will become inundated with tannins, which then travels from the surface of the wood to the surface of the paint.

How Can Tannin Bleed Be Prevented?
Thankfully, tannin staining can be prevented and corrected. One of the best ways to avoid bleed-through is to apply either an oil or alkyd-based primer or shellac. We’d like to point out, though, that even with an oil/alkyd primer, tannin bleed can still occur.

Shellac seems like the better preventative option as many painters have found stains much less likely to appear once they’ve painted over it. Regardless of which of these sealing methods you use, it’s best to err on the side of caution and apply two coats.

If you’ve already got stains, then you’re going to need to find where the source of moisture is, fix it, and let the wood dry for at least 48 hours. If the paint is peeling off the wood’s surface, then remove it with a scraper or wire brush.

The stains themselves can be taken care of with oxalic acid (it breaks the stains down into something that can be easily rinsed away) and then wash them away with a pressure washer - again, be sure to let the wood dry for approximately two days. After you’ve done all of that, you can prime the wood with two coats of oil/alkyd or shellac and repaint it.

Tannin bleed can be incredibly frustrating, even more so for people who’ve just started their painting careers and may not know what’s going on. Tannin stains are a surface issue, however, not a problem within the wood itself. So hopefully, now that we’ve told you what tannin staining is and how to prevent/repair it, painting has become less of a pain and more something that you enjoy (or at least like to do to pay the bills).

If any painters out there have any more advice on how to control tannin bleed and want to share with your fellow painters, the comments section is where to do it!