Let’s say there was a leak in the drain for an upstairs bathroom that left a brown stain on the drywall below. No problem – you painted it with latex paint left over from painting the ceiling, and at first, it looked great. But a week later the stain started to bleed through the paint, and eventually, it looked just as bad as before. Now how do you fix it?
Primers and stain killers need to be applied over stains before you use latex paint. Typical latex paint doesn’t have the capacity to cover serious stains and watermarks. Primers and stain killers have special binders and covering agents that can block stains and provide an excellent base for latex paint.
What is a good primer? For interiors, KILZ and BIN are excellent stain blockers. Where there is a water stain, remove any loose material, patch, and then apply the primer. If the drywall and paint are solid, just paint over the stain. BIN actually contains shellac; professional painters have used this stain-killer for many years.
Many manufacturers make specialty primers that work well to cover most stains.