Once sanded, stained wood trim accepts new layers of paint easily. But over time, the stain can seep through the paint. The discoloration is most pronounced if you are using white paint or a very light-colored paint. Fortunately, some additional wood preparation can prevent stain bleeding. With the right prep work, you can cover even the darkest stained wood with a crisp white finish.
Go over the wood with 150-grit sandpaper. Sanding removes surface imperfections, along with the top layer of gloss from a previously finished wood surface.
Go over the wood trim again with 220-grit sandpaper. This fine sandpaper buffs the surface for a smoother final finish.
Clean off the sandpaper dust with a damp rag.
Protect wall surfaces with painter's tape, and lay protective plastic sheeting on the floor.
Apply stain-blocking primer to the wood trim, using a paintbrush. Stain-blocking primer is an exterior primer designed to prevent natural redwood and cedar oils from seeping to the surface. It works equally well on artificially stained woods. With this primer, your white trim will stay bright and clean for years to come. Wait for the primer to dry before proceeding.
Paint the primed wood trim using a foam brush and white oil-based paint. Apply a second coat after the first coat dries in one to two hours.
Remove the painter's tape after the final coat of paint has dried for a full 24 hours.