How to Add Acetone to Spar Urethane

Use a drill with a mixing paddle to blend in the acetone.

Spar urethane is a thick finish designed primarily for exterior applications. When it hardens, it provides an excellent layer of protection from dirt and moisture, and multiple coats can protect any surface for years. Unfortunately, these same characteristics make it a difficult finish to use, and many people choose to thin it down with acetone to make it more user-friendly.

Things You'll Need

• Mixing paddle
• Mixing container
• Drill
• Clean rags

Instructions

1. Wipe off the top of both the acetone and urethane containers with a clean rag. This will prevent contaminants from entering the finish and ending up on your coated surface.

2. Mix the urethane thoroughly using the drill and paddle wheel before adding the acetone. Remove the mixer, then measure out and pour the acetone into the urethane. A 50-50 mix for the first coat will make it very thin, and help it penetrate the wood. If you're spraying the finish, each coat will be a 50-50 mix, but when applying the spar urethane with a brush or roller, the acetone shouldn't exceed 10 percent for successive coats.

3. Mix the acetone into the finish thoroughly using the drill-mounted mixing paddle. Inadequate blending will result in a blotchy looking coat, and can even clog spray tools. Move the drill in an up and down motion to help the process.

4. Continue mixing the finish during the entire application process. The acetone can settle unevenly throughout the urethane over time, and periodically mixing the finish will prevent unwanted problems, and allow the finish to lay out properly.

References

• Woodworker's Journal; Spraying Polyurethane; Michael Dresdner; May 18, 2004