Leaking water pipes, a hole in the roof and an overflowing bathtub or sink can all create water damage on walls. Many times the water damage is not severe, but leaves a stain on the wall. As the water dries, it discolours the wall, leaving behind a brown or yellow stain. Painting over a wet spot with standard wall paint is typically not successful. The wet spot stain bleeds through the paint even after several coats of standard paint. Hiding a wet spot requires more than just regular paint.
Examine the wall to determine if the wet spot is completely dry. If you are unsure, set a fan to blow directly on the wall to dry the area. Allow the fan to blow on the wall until the wall is no longer damp. You cannot hide a wet water stain.
Clean the stained area with a powdered detergent and a sponge. Sprinkle the detergent onto a dry sponge and scrub the wall. Vacuum detergent residue off the wall using an upholstery brush attached to a vacuum hose. Choose a detergent that you do not have to rinse.
Open a can of latex or shellac-based, commercially available stain killer or all-in-one stain-killer primer. Stir the stain killer with a painter's stirring stick.
Pour the stain killer into a painter's tray or small bucket.
Dip a paintbrush into the bucket or roll a paint roller through the stain killer in the painter's tray. Wipe off excess stain killer on the side or the bucket or roll off excess on the raised end of the paint tray.
Paint the stain killer over the wet stain on the wall and extend 12 inches past the edge of the stain. Some water stains may spread over time and painting past the line of the stain will allow room for the stain to spread without affecting the wall. Allow the stain killer to dry for two to three hours. Apply a second coat of stain killer and let it dry for two to three hours.
Apply a coat of primer over the stain killer with a paintbrush or roller if you did not use an all-in-one stain-killer primer. Let the primer dry for two to three hours.
Paint on two coats of paint with a paint roller or paintbrush allowing each coat to dry for two to three hours between applications.
Many all-in-one stain-killer primers also block odours, which is convenient if a pet left a wet mark on the wall.
Do not apply stain killer, primers or paint to a wet wall as the paint adhesion will fail and the coating will bubble off the surface.