Polyurethane Coatings Procedures

Polyurethane Coatings Procedures explains the process of coating natural unfinished woods for use in interior spaces. This process was developed in the ATTB construction process which included the coating of both furniture and entire cabin interiors. This process is only for interior woods. Polyurethane degrades in sunlight and will cloud, brittle, flake, or yellow when used in exterior applications.

Materials List

• Minwax Oil-Modified Polyurethane Gloss or Semi-gloss (Amazon)
• Minwax Oil-Modified Polyurethane Satin (Amazon)
• Fine sand paper for palm sanders (100-180 grit for softwoods like Pine, 180-220 for hardwoods like Oak)
• Tack Cloth (for dust removal)
• Mid-grade synthetic brush
• Fine sanding sponge

Application Pointers

• Minimize pouring and stirring poly in the can. Stir slowly only until poly is uniform. Don’t shake. Disturbing poly too much will cause foaming or small bubbles that will show up in dried coat.
• Don’t wipe your brush on the can or cup. This will cause foam to build up on the brush and transfer in the coat.
• First coat should be heavy.
• Apply in small sections and return to check for “runners” and “skippers”. Runners are drips running down surfaces or hanging on edges. Skippers are dry spots where poly soaked in or was applied to thinly. Poly dries to tackiness quickly. Depending on humidity, you can only retouch wet poly after 5-10 minutes or your brush strokes will not settle out of the finished coat.

Application Process

1. Sand the wood to prep for coating. Surface should be smooth and clean. Spray off or vacuum dust.
2. Wipe wood with tack cloth to remove dust. Start by unfolding tack cloth and gathering in loose wad. Frequently spread and wad to keep fresh cloth in contact with wood. Discard as tackiness decreases.
3. Coat with first coat of gloss poly. Use a heavy coat, checking every 5-10 minutes for runners and skippers.
4. After dry, wipe with fine sanding sponge. Don’t sand back-and-forth. Just wipe once in one direction. Check with hand to confirm smoothness.
5. Wipe clean with tack cloth.
6. Apply second coat of gloss. The wood is sealed, so it should take significantly less. Remember to check for runners and skippers.
7. Knock down roughness with fine sanding sponge again.
8. Clean with tack cloth.
9. Apply third coat, but use satin finish poly this time.

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