Things You'll Need
Plastic drop cloth
Wagner makes an airless sprayer geared toward small jobs around the house, like painting fences, doors or small pieces of furniture. It is easy to use and delivers a large amount of paint in a very short time. Although not precise enough for spraying thin, fast-drying clear coats such as lacquer, the sprayer offers an alternative to brushing for heavier materials like varnish and polyurethane, which dry more slowly.
Prepare the work area by covering anything that may be in the way of the spray that you don't want to paint. Mask off windows and doors. Cover furniture and carpets with drop cloths. If you are working inside, separate the room you are working in from the rest of the house by hanging plastic in the doorway.
Shake the can of polyurethane vigorously and open it. If it is flat or semi-gloss, give it an extra stir to mix in the flattening ingredients. Use the paper funnel to pour the polyurethane into the spray cup, filling it about three-quarters full. Screw the cup onto the sprayer and plug it in.
Test the sprayer on an inconspicuous surface. If it doesn't spray in a full, even fan, remove the cup, add thinner and re-test.
Hold the sprayer about 18 inches from the object or surface you are painting and begin spraying in steady, even strokes from top to bottom or from left to right. Don't linger. There is a lot of material coming out and it is very easy to spray too much, causing drips or puddling. For large surfaces, overlap to the middle of the previous spray pattern.
When you are finished, remove the cup and pour the remaining polyurethane back into the can. Fill the cup with thinner and spray thinner for about 10 seconds. Remove the cup and then unscrew the tip and submerge it in thinner. If you can, leave it in the thinner for a hour, or even overnight, before wiping it clean with a rag.
Sand the surface you have sprayed after the polyurethane has dried (about 24 hours). Apply a second coat in the same way. Repeat as many times as you wish, but two coats are usually sufficient.
There are solvent-based and water-based polyurethanes, so make sure you know which one you are spraying. Use mineral spirits or lacquer thinner to thin solvent-based polyurethane.
Solvent-based polyurethane is toxic to breathe, so use a mask and allow plenty of ventilation for drying.
Wipe up spills and drips immediately because dried polyurethane is very difficult to remove.
Airless spray is dangerous. Never spray directly at yourself or anyone else.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.