McPherson Quality Painting and Water Proofing
Tannin stains are brownish or tan discoloration on the paint surface caused by tannins that have bled through the paint film. Tannic acid exists in many wood types, but it is much more noticeable on cedar, redwood, mahogany and fir. It may also occur over painted knots in certain other wood species, most notably, some types of pine.
Tannic acid stains are more likely to form on newer, "green" woods. Tannins inside the wood are carried to the surface by moisture, bleeding through the paint film, leaving a yellowish-brown stain on the surface. These stains are more noticeable on lighter paint colors and must be completely removed before repainting.
· Failure to adequately prime and seal the surface before applying the paint.
Using a primer, that is not stain-resistant.
Excess humidity or other moisture escaping through the exterior walls, which can transport the tannins to the surface of the paint.
1.) Locate and correct any moisture sources.
· Repair any loose caulking and patching material. Avoid
caulks that can crack, shrink or lose adhesion.
· If necessary, repair the roof, clean gutters and downspouts and cut away heavy vegetation if it is near an area that is stained.
· If moist air is originating inside the building, consider installing vents, exhaust fans or dehumidifiers, especially in kitchen, bathroom and laundry areas.
2.) Remove all loose paint with a scraper or wire brush.
the stains with oxalic acid or an oxalic-based solution, such as Okon Wood
4.) Rinse with a pressure washer.
5.) Allow the surface to dry thoroughly for at least 48 hours (depending on the existing weather conditions).
6.) Prime the stained area with a top-quality, stain-blocking wood primer such as Compo (42-1) or E-Z Prime (W 708). If severe staining exists, apply two coats of primer. Always prime board or siding shingle edges and ends. If possible back prime prior to installation. These procedures will help prevent moisture from entering the wood.
Tannic acid will prolong the drying of oil based primers and in some cases you will have to wait three to five days for the primer to fully cure before repainting. If staining occurs during the application of the new coat of paint, sand lightly and reprime the area before applying the final finish.
Note: In spite of all precautions, a certain amount of bleeding will probably occur within one year after the wood is first painted. It is best to wait one year before repainting. This allows the tannins to surface and weather away normally. This is a surface problem - not a paint failure.
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