Painting Tip: Tannin Staining
DEFINITION TANNIN: Okay, right from the start I suppose I should tell you what Tannin is. It’s something you’ve probably seen, a tan or brownish discoloration on the paint surface that the paint just won’t cover up. Here, courtesy of Wolman Wood Care Products is probably the best definition of tannin that I‘ve come across:
Tannin (or Extractive) Bleeding: Redwood, Cedar and Douglas Fir are examples of wood species that contain naturally occurring, water soluble chemicals that tend to migrate to the surface with exposure to extracting agents such as water. After rain or heavy dew, coffee or tea-colored stains may appear on the wood surface. If the wood is coated, discoloration of the coating may occur when tannin extractives are dissolved into the coating solution by water, reach the surface and remain as dark, coffee-brown stains after the water evaporates. This reddish-brown bleeding is unsightly, but not damaging to the coating.
SOLUTION:
- As in many paint problems moisture is sometimes an issue and it certainly contributes to the tannin problem – - so look for and correct those. Get that surface as dry as a bone!
- You can remove the existing stains with oxalic acid. Just Google oxalic acid and you’ll find information about it and products that contain it. It’s basically wood bleach.
- Next you should rinse the wood off with a pressure washer. You can rent pressure washers from Home Depot’s that have Tool Rental departments.
- Let the surface dry completely.
- Then, I recommend using Dunn Edwards Premium E-Z Prime (W708) – Acrylic Wood Primer to prime the surface. This will really help to prevent stains from bleeding through. If the stains are severe I would suggest two coats of primer.
- Final coat with high-quality paint in the finish you want.
This should handle most stain problems. However, it’s possible that some bleeding my happen within a year after you’ve painted the wood. Don’t repaint it as soon as this occurs. Wait a full year as this will let any remaining tannins to come to the surface where they will weather away naturally.
All the best,
Perry
714 721 3050