Question of the month: how do you paint damp walls?

Damp walls pose a challenge when painting. Fortunately, with the right preparation, techniques and products, it is possible to achieve a durable and professional result. In this article, you will learn how to effectively treat and paint damp walls. 

Before you start painting damp walls, it is crucial to address the cause of the moisture problem. In the case of a burst pipe, for example, it is logical to repair the pipe first before proceeding with wall preparation. By treating the underlying cause of the moisture, you prevent the problem from recurring and ensure a more durable paint finish.

Have you identified the cause of the moisture problem and dealt with it? Great! You are now fully ready to paint the wall. This is how you proceed:

Painted substrates – interior 

Assess the condition of the substrate. Do you see dark rings or dissolved moisture stains (“coffee stains”)? These can be sealed with Zinsser® Bulls Eye 1-2-3 Plus or B-I-N® Aqua due to their slightly acidic pH. Do not attempt to seal them with standard wall paint.

Allow the coat of Bulls Eye 1-2-3 Plus or B-I-N® Aqua to dry before finishing with a paint such as Zinsser PermaWhite. Thanks to PermaWhite’s moisture-resistant film, you prevent ambient moisture from causing damage again. In addition, PermaWhite protects the dry paint film against mould growth.

Painted substrates – exterior 

Largely the same approach applies to exterior substrates. However, in this case we recommend Allcoat® Exterior, especially if you are painting outdoors in autumn. Allcoat Exterior is a fast-drying primer and finish in one, suitable for almost any substrate and offering excellent weather resistance. Although the coating is touch-dry after one hour, we still recommend ensuring that no rain is expected within 24 hours of application.

Unpainted substrates – interior and exterior 

Watertite is an ideal moisture-problem-solving primer for treating damp, unpainted basement walls and for sealing concrete basement floors. It can also be applied to the exterior of foundations and retaining walls, both above and below ground level. In short, Watertite is the solution when you are dealing with significant water exposure, for unpainted substrates both indoors and outdoors.

Of course, everything depends on the specific situation you are facing. Suppose moisture from rainwater is seeping through your unpainted brick garage wall, but you still want to apply a coat of paint. You can address this by first applying a layer of Zinsser® Watertite to the interior side of the wall. Watertite is resistant to water pressure and will therefore hold back the moisture. Keep in mind, however, that re-treatment after a few years is always recommended.

Wooden substrates deserve a separate mention due to the unique ways wood reacts to water. As with any material, first check the extent of the damage. If the wood has rotted due to prolonged exposure to moisture, this cannot be resolved with a primer—you must replace the damaged wood first. You can easily test for rot by probing the wood with a long, thin object. If it goes all the way through, the wood is rotten. You can also use a moisture meter for a more precise assessment. 

Do you see stains on the wood? Stains may indicate the presence of tannins. You can seal an interior wooden substrate with Zinsser® B-I-N® Aqua. If the problem occurs outdoors as well, use our solvent-based Zinsser® Cover Stain®. Never apply water-based paint directly to hardwood, tannin-rich wood or tropical wood (such as oak, cedar or mahogany). Doing so will cause bleeding to reappear. 

Want to learn more about painting wood? Find more information here on painting interior wood and exterior wood.