How to Spray Single Stage Urethane Auto Paintby Chris Deziel
Single stage urethane is a one-step painting process for automobiles that avoids the necessity of a clear-coat finish. The paint is durable enough to polish without altering the color tone, and using it reduces the overall refinishing time. The urethane must be mixed with a hardener and reducer before spraying and, while the ratios may vary from product to product, the typical ratio is 4 parts paint to 1 part hardener to 1 part reducer.
Apply rust conditioner to rusty areas and use a plastic putty knife to fill holes and dents with body filler. Feather the filler into the body with sandpaper.
Mask off all areas not to be painted with tape and masking paper. Apply the tape carefully to avoid messy cleanups of overspray later. Make sure you tape down the sheets of paper to prevent overspray from going underneath them.
Fill the cup of the spray gun with primer and turn on the compressor. Test the spray pattern, rotating the nozzle of the gun and the air pressure from the compressor until you get a vertical spray pattern about 8 inches wide from a distance of 6 inches.
Holding the gun 6 inches from the surface, begin spraying in a left-right motion from end to end, overlapping about half the width of the spray pattern. Move at a speed that will leave a shiny surface of paint without runs, drips or separation. When you are finished, rotate the nozzle 90 degrees and spray again in an up-down pattern. Let the primer dry for 2 hours.
Lightly sand the primer with 220-grit sandpaper and tack the surface.
Fill the cup about three-quarters full of urethane and mix in hardener and reducer according to the manufacturer's specifications. Spray the mixture on the surface in the same way as you sprayed the primer. Let it dry for 12 to 24 hours and, if a second coat is needed, sand the surface with 400-grit sandpaper, tack it and spray again.
Let the finish cure for 24 to 48 hours before buffing it out and applying wax or polish.
- It is best to spray in a spray booth; but if you have to spray outside, the ideal conditions are cloudy, windless days when the temperature is between 70 and 80 degrees Fahrenheit.
- If the paint runs or drips, wait for it to dry before knocking down the drips with sandpaper. When you spray again, try holding the gun a little farther away or moving it faster.
Things You'll Need
- Body filler
- Putty knife
- Orbital sander
- Rust conditioner
- Masking tape and paper
- Air spray gun
- 220 and 400 grit wet/dry sandpaper
- tack cloth
- The solvents in urethane are harmful to breathe. Use a respirator and make sure the spraying area is well ventilated.
Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.