Staining over paint may seem counterintuitive, but it's an efficient way to achieve a host of interesting effects as well as to save fading paint. You can use water- or oil-based,liquid or gel stains to make an antique glaze, darken an existing color or fill in color on old painted furniture as an alternative to repainting.
What Stain to Use?
The best choice of stain depends on the project. If you're glazing or antiquing, you may prefer a gel stain, which acts more like a glaze than a liquid stain does. Choose a water-based stain -- it adheres better to painted surfaces than oil-based stains, which excel at penetration. A liquid stain may be a better choice when patching up a faded or peeling paint job, and for this job, an oil-based product is probably the better choice. It sinks deeply into exposed bare wood while being easier to remove from painted surfaces.
Preparation and Application
Clean the surface thoroughly with detergent and water. A strong detergent, such as trisodium phosphate, will ensure that no greasy or waxy spots remain to repel the stain. Mix a solution consisting of 1/2 cup per gallon of water. Protect yourself from its corrosive properties by wearing gloves and goggles while washing the surface with it, using a sponge or rag.
Whether you wash with a mild detergent or with TSP -- which is strong enough to etch the paint -- you should scuff those parts of the painted surface to which you want the stain to adhere, using 150-grit sandpaper. You don't need a machine to do this -- hand-sanding is sufficient.
Spread the stain generously on the painted surface with a brush or rag, working it carefully into crevices and around molding. This is especially important if you're after an antiqued look.
The quality of a paint job depends on how well you spread the paint, but when staining over paint, the quality of the job depends on how you remove the stain. Wipe hard enough to remove any stain that remains on the surface or you'll see streaks. If you prepared the surface well enough, the stain will settle in the pores you created in the paint. You don't want to wipe too thoroughly, though, or you'll remove all the stain you applied.
You may not get the effect you're after with one application of stain. If not, add more -- after waiting for the first coat to dry.
Unlike paint, stain has no binder -- it's all pigment and solvents -- so you have to protect the surface with a clear coat. Polyurethane, acrylic, water-based lacquer and solvent-based lacquer are all appropriate finishes, and most should adhere well, since you've already etched and scuffed the surface.