Brush marks in polyurethane

Likely causes

The causes the most sources give come first.

1. Brushing back into finish that has started to set, or brushing it out too much.

   Two sources: Rust-Oleum (RPM) and General Finishes , sources [1, 2]

2. Too little finish on the surface to flow out, or a finish too thick to level.

   Two sources: Mohawk (RPM) and General Finishes , sources [3, 2]

How to tell which

None of the sources we read says how to tell these causes apart. Check each one against how you finished the piece.

The fix

1. Once the coat is dry, sand the flaw level with fine paper, wipe off the dust and put on another coat. The makers name 220 grit (Minwax), 220–320 (General Finishes) and 400 for sprayed lacquer (Target).

   3 sources agree , sources [4, 5, 6]

Next time

1. Keep a wet edge, so each pass blends into the last before it sets.

   3 sources agree , sources [7, 1, 8]

2. Lay on a full, wet coat with the grain in long, even strokes, and leave it to level.

   Two sources: General Finishes and Rust-Oleum (RPM) , sources [2, 9]

3. Varathane says to sand lightly before recoating any coat of its Crystal Clear that has dried more than 24 hours, to avoid brush marks.

   One source: Rust-Oleum (RPM), the maker of that product , sources [10]

Often comes with

• Bubbles in polyurethane
• Orange peel

The finishes it applies to: oil-based polyurethane, water-based polyurethane, wipe-on polyurethane, spar urethane. Every other problem: the finish troubleshooter.