I build DIY furniture, I am often painting wood. Sometimes it’s new raw wood, and sometimes I’m covering up an old finish. White and light colored paint are particularly tricky because they are susceptible to tannin bleed through staining.
What are tannins? Tannins are natural occurring compounds found in many plants (including coffee, tea and grapes/wine). Wood contains tannin as well and it tends to seep to the surface, even after the wood is completely dried. Red colored wood is the worst culplrit, although it doesn’t have to be naturally pigmented to cause problems as well.
More than once, I’ve gone through the recommended steps (sanding, priming, two coats of paint, 2-3 coats of clear) to paint a cabinet or old piece of furniture, just to see little pink spots coming to the surface. It’s so frustrating!
How to Prevent Tannin Bleed Through
Sometimes it’s small spots and sometimes it’s large, discolored blobs, but tannin is almost always to blame. I’ve tried just about every kind of primer you can buy, but even with “stain blocking” primers, I’ve experienced bleed-through. The only product that has yet to fail me is my old standby shellac.
I’ve used shellac for a long time to get a smooth finish when painting MDF, but it also makes an amazing tannin blocking primer as well. It comes in a brushable formula or in an aerosol can.
Shellac tries very quickly and can be covered in any kind of finish (oil-based, water-based, lacquer, etc.). I have started applying a coat or two prior to painting, every time I’m using a light color.
Now what if you just have one or two problem spots? Knot holes can cause particular trouble.
Sometimes the painted surface will look perfectly even, then days, weeks, or even months later those dang tannin stains from the knots work their way out.
When I built my modern bachelor chests, I primed the raw wood with BIN, stain blocking primer and thought I was good. Sadly, after a couple months, the knots started to rear their ugly heads.
However, I’ve recently discovered a secret weapon. Clear nail polish! Yep, the simple top coat you use for your manicure can seal those stubborn knots.
It’s easy to brush on one or two coats onto problem areas, without having the cover the entire surface. I’ve also used this trick to seal spots that have been touched up with a stain pen, which I’ve discovered is almost impossible to cover.
In the sample board below, you can see the indention from the knot (easily smoothed out with wood filler), but all the dark pigment is safely sealed beneath the surface.
So next time you pull out the white paint, make sure you tackle the tannin first! Grab yourself some shellac and a bottle of clear nail polish, and you have a simple solution for bleed through.
More woodwork and finishing tips:
Step by step tutorial: How to refinish wood furniture (with minimal sanding)
Painting furniture: When to use 5+ different types of paint