Water stains or water damage of any kind is an ugly sight—especially if you painted those walls yourself. Whether it’s because the roof leaked, a pipe failed, or someone upstairs let the bathtub overflow, if there’s water inside a wall, the temptation is to paint over the area as soon as possible. The painful truth is that you shouldn’t do anything about it—yet. The drywall has to be an actual dry wall before you can successfully fix the water stain left behind. Here’s how to paint walls that have water stains or have water damage.
First things first: find the source of the water, fix it, and mop up any water in sight. Then, wait for the moisture to finish moving—water has a tendency to wick down and across walls, spreading out long after the leak stops. Anywhere moisture is still present, fresh paint will pop right off.
A moisture meter will tell you exactly how wet the walls are and, depending on the reading, indicate what you should do. If the leak is excessive there may be damage to the drywall or plaster. In this case the substrate will stay soft and should be replaced. When the reading of a moisture meter is below 10% it is safe to paint.
Where the damage is minimal and the surface can be left to dry out it’s very likely the water has left a stain behind. This stain will bleed through most if not all water-based coatings. To avoid this and seal the stain, choose a stain-blocking, alkyd-based primer, like Benjamin Moore’s Fresh Start Multi-Purpose Oil Based Primer #024. If there is mildew present it must be removed prior to any painting: Use a solution of 8 parts water to 1 part bleach to clean the area completely until all residue of mildew is gone. Allow the surface to dry completely before painting. Scrape away any blistering, scaling paint and sand the surface smooth. Apply #024 to the wall at a temperature between 50 and 90 degrees, using a china bristle or nylon/polyester brush or a roller. This primer is a good universal undercoat, sealer, and stain-blocking primer all in one. It can also mask crayon, grease, rust, and smoke damage.
Tip: to help disguise the repair and touch-up, use the same type of applicator that was used to paint the surface originally. Also, if the surface needs to be spackled to get a smooth finish, prime first then repair with patching compound and sand smooth before re-painting.
Link back for the August 2010 Stain Stoppers post: http://paintgurus.typepad.com/blog/2010/08/stain-stoppers-primers-that-block-bleedthrough.html