Why is There Bleed Through After Painting Pressure Treated Lumber?

Pressure-Treated Lumber

• Pressure-treated lumber is beneficial because of its durability and resistance to insects and decay. The wood is treated by forcing chemical preservatives into the wood while the wood is sealed in a vacuum chamber. Generally, the chemicals are classes of waterborne, oilborne or creosote preservatives, but the specific chemical varies by manufacturer.

Properly Painting Pressure-Treated Lumber

• Pressure-treated lumber should generally be allowed to age until the lumber has fully cured. Typically, this takes six to 12 months but it can take longer. After the wood has fully cured, it will turn grey and can then be painted using an oil-based primer. The wood can also be treated with a pressure-treated wood preservative prior to curing to avoid possible exposure to copper-coated arsenic, which is a potentially dangerous chemical used in some pressure-treated wood. Many of these wood preservatives are accompanied by special instructions for painting after application of the preservative.

Why Bleed-Through Happens

• Bleed-through happens when the chemicals from the pressure-treated lumber eat away at paint or stain from the inside. This may happen because the treated lumber has not been allowed a sufficient amount of drying time before painting or staining. As the chemicals and moisture from the treated wood leach out under the layers of paint, they can dissolve the paint or cause moisture bubbles.

Ways to Fix Bleed-Through

• If paint bleeds through or bubbles, it should be removed from the wood. This can be accomplished by power washing or other removal method. Once the paint is removed, the wood should be allowed to dry for at least 12 months or until it turns grey. Then it can be repainted.