How to Coat a Garage in Polyurethane

Health and environmental concerns about volatile organic compounds have fostered the use of water-based polyurethane as a protective floor coating. Oil-based polyurethane is still used, however, especially in garages and other settings that can be thoroughly ventilated. Both polyurethane types are good clear “top coats” for wood and painted floors, including garage floors. Polyurethane is easy to apply, though it’s important to work carefully. With water-based polyurethane, which dries very quickly, it’s also important to work quickly and maintain a “wet edge” to prevent application lines.

Tack cloth
All-purpose cleaner
Firm-bristled push broom
Rubber boots
Protective gloves
Safety glasses
Ventilator mask (for oil-based polyurethane)
Painting pad (for water-based polyurethane)
China-bristle brush (for oil-based polyurethane)
Pole-type applicator
Synthetic-wool applicator pad (for water-based polyurethane)
Lamb's-wool applicator pad (for oil-based polyurethane)
Paint thinner or mineral spirits (for oil-based polyurethane)
Pole sander
100-grit sandpaper

Instructions

- 1
  Wait two or three days, if you’ve just painted your garage floor, to let the finish fully dry before applying polyurethane. Vacuum the floor and then wipe it with a tack cloth to pick up any lint, dirt or grit that will mar the surface.
- 2
  Clean the garage floor carefully, if you’re applying polyurethane over older paint. Sweep the floor, using a small paintbrush to clean out garage corners. Scrub it with cleaner solution and broom. Hose down the floor and allow it to dry. Wipe the surface with a tack cloth.
- 3
  Apply three or four thin coats of water-based polyurethane for a crystal-clear coating that’s very scratch resistant; look for “nonyellowing” on the label. Apply two or three thin coats of oil-based urethane for the hardest possible surface — and if you don’t mind waiting 12 to 24 hours for drying between coats.
- 4
  Prepare the top coat according to product directions. Many polyurethanes, both water- and oil-based, require adding the hardener just before use. You can also add nonskid particles, for a safer, less slippery walking surface.
- 5
  Start in the corner farthest from your exit. For water-based polyurethanes, use a painting pad for garage edges and corners and a synthetic-wool pad for general application. For an oil-based topcoat, finish the corners and edges with a china-bristle brush and use a lamb’s-wool pad for the rest of the garage.
- 6
  Cut in edges and corners as you go, with water-based polyurethane, which dries very quickly. Apply coating in one direction, working fast to keep a “wet edge” and avoid leaving lap marks. Do not go back and “rework” any areas, or you’ll leave lines that will be visible when the surface dries.
- 7
  Cut in edges and corners first, if you wish, with oil-based polyurethane, which dries very slowly and lets you to go back and rework rough spots. Make sure the garage is well ventilated — garage door and windows open — and wear your ventilator at all times.
- 8
  Sand the previous coat of polyurethane lightly, using the pole sander and 100-grit sandpaper, before applying the next. Vacuum the surface well and wipe it with the tack cloth. Do not sand the final coat of polyurethane.

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