Sealing painted wood provides an essential layer of protection for furniture and decorative pieces, especially items such as tables, desks and kitchen chairs that are subject to the rough-and-tumble use of everyday living. In addition to keeping the paint from chipping and peeling, the sealant makes cleaning up spills and marks easy, and adds a layer of depth and shine that give the piece a finished look. The first step in sealing painted wood is to choose a sealant that fits your purpose.
Many sealant are products on market, some of which can be used for both bare wood and painted wood. Sealants that are suitable for use over painted wood include the following:
Polyurethane is a synthetic, oil-based varnish that deposits a highly durable and protective coating on painted and bare wood surfaces. It is manufactured in liquid forms that you apply with a brush or in a spray can. Because it emits potentially toxic volatile organic compounds, or VOCs, when wet, it must be applied outdoors or in a well-ventilated area. Cleanup requires paint thinner or mineral spirits. It can't be removed by stripping, so if you decide to refinish a piece sealed with polyurethane, you must sand and scrape it off.
Polycrylic is a water-based finish coat that applies with a brush, gives off little odor, and cleans up easily with with water. It holds up well but is not as durable as polyurethane. Many people prefer polycrylic, however, especially for children's furniture, because it is low-VOC. Polycrylic appears white or milky when wet, but it turns clear when dry.
Paste wax consists of a wax dissolved in solvent. The wax may be a naturally occurring substance such as beeswax or carnauba. The product is applied with a brush or rag and the excess wiped off. After it has dried, it must be buffed to reveal its shine. Wax finishes may be clear or colored to create an antique look and are most suitable for use over chalk paint or milk paint. Wax can also be applied over polyurethane to achieve a richer appearance and softer feel. Wax finish is not especially durable, and it is recommended that the wax be re-applied at least yearly. Waxed furniture should be kept away from high heat or direct sunlight, because the wax can soften and become sticky or melted.
Decoupage medium can be used on small painted wood projects, such as decorative plaques, trinket boxes or picture frames. Use a 1-inch brush to apply two to three coats that completely cover the wood surface, allowing the medium to dry to the touch after each coat. Sanding between coats is not needed. Let the medium dry for 24 hours after the final coat.
Paint-and-sealer combination products have appeared in recent years. The sealer is contained within the paint mixture, so additional topcoats are not needed. Follow the product instructions for preparation and application. These products are useful for painting furniture white or light colors because they are less prone to discoloration. Some sealants, including polyurethane, may turn yellow over time, producing a noticeable discoloration on white paint.
Applying a Brush-on Sealant
Every product has specific instructions from the manufacturer, so be sure to read the label before you begin. These steps are a general guideline for applying polycrylic or polyurethane sealants.
Check to make sure the final coat of paint is thoroughly dry. Sand it lightly with 220- to 320-grit sandpaper, using just enough pressure to smooth any rough spots. Wipe the surface with a tack cloth to remove the sanding dust.
Dip a clean paintbrush into the can of sealant. Stir the sealant gently if needed, but avoid heavy stirring or shaking the can, as it may introduce bubbles into the fluid. Tap off excess sealant on the edge of the can.
Paint the sealant onto the surface, stroking from edge to edge, evenly and in one direction. This will provide a smooth finish when the sealant is dry. If you notice any bubbles or drips, smooth them out with just the edge of the brush while coat is still wet. Allow the sealant to dry for one to two hours, or according to the product directions.
Sand the dried coat very lightly with 220- to 320-grit sandpaper. Remove the sanding dust with a tack cloth.
Apply the next coat of sealant. Let dry, sand and repeat for an additional one to three coats of sealant. You don't need to sand after the final coat. Let the finished piece stand overnight to begin curing or according to product directions, before putting it into use.
If you are using a water-based sealant or polycrylic, use a synthetic bristle brush. Use a natural bristle brush for polyurethane of oil-based sealants.
When using polyurethane or any product that emits volatile organic compounds, always follow the manufacturer's safety warnings. Work outdoors or in a well-ventilated area, away from open flame. Wear a mask over your mouth and nose and use latex or rubber gloves to protect your hands.