Spray-painting a door is the best option for a completely smooth surface, with no problems of brush or roller marks. Airless or high volume, low-pressure (HVLP) sprayers make it possible to paint several doors at one time. HVLP sprayers are considered easier to use and have less risk of overspray -- the paint mist that settles on surrounding areas while spray-painting an object. An airless paint sprayer is quicker, but needs greater control. Freshly sprayed doors can improve the overall appearance of your home's interior, and the process is fairly simple -- provided you take your time.
Remove your doors from their hinges by using a small hammer and screwdriver to tap the pin up and out of each hinge. Take the doors to your garage or another utility building for painting.
Unscrew the doorknobs, striker plates and hinge leaves from the door, to prevent them from being sprayed. Set them aside.
Scrape off all loose or chipped paint with a paint scraper. Work carefully so you do not damage the doors -- any flaws on a smooth door will look worse when they are painted.
Sand new, unfinished wood doors with a sanding block loaded with 120- or 150-grit sandpaper. Fill all imperfections by applying spackle or auto body filler with a putty knife, following the product directions. Sand the areas smooth when the material has dried.
Clean previously painted doors with soap and warm water to remove all traces of oil that collects from being touched repeatedly by people's hands. Apply a liquid sanding product to remove any remaining soap, following the label directions.
Prime each door with oil-based enamel undercoat, using a paintbrush. Let the primer dry, which could take up to 24 hours.
Hand sand the entire door with 220-grit sandpaper. Wipe the doors with soft rags and vacuum with a brush attachment to get rid of all the sanding dust.
Spread dust sheets on the floor. Position the doors on the dust sheets. Insert wood blocks beneath the doors to raise them off the dust sheets.
Add a paint conditioner that's appropriate for your type of paint -- water-based or oil-based. Mix the conditioner according to the manufacturer's directions; generally, you should enough conditioner so it floats on the surface of the paint.
Transfer your paint into a sprayer. Opt for a small spray tip to achieve a more precise finish.
Prevent overspray by placing cardboard shields between your doors and anything you want to protect. Hold one of these shields in the direction of the overspray when applying the paint.
Start the sprayer and paint the doors with wide, sweeping motions, going beyond their edges. Apply a light first layer. Let it sit for 20 minutes, then apply a second coat. Repeat this process until you are satisfied that your doors have a solid coating of paint.
Let the doors dry overnight.
Turn the doors over carefully. Paint the unfinished sides, using the same priming and spraying process you used on the first sides.
Allow the finished doors to dry overnight before reattaching the hardware with a screwdriver and reinstalling the doors.