Polyurethane Finish — Lutherie Encyclopedia

Polyurethane FinishType: techniqueA durable, plastic-based finish that provides excellent protection against wear and environmental damage, common on production instruments.## Overview Polyurethane finish is the most durable option available for guitar finishing, offering superior resistance to scratches, chemicals, heat, and moisture compared to nitrocellulose lacquer or shellac. It is the standard finish on most production guitars manufactured since the 1970s. While some players and builders believe polyurethane dampens tone due to its thicker film build, modern catalyzed polyurethane and polyester finishes can be applied quite thinly when proper technique is used. ## Process Polyurethane finishes are available in both oil-based and water-based formulations, as well as two-part catalyzed systems. For guitar finishing, catalyzed (two-part) polyurethanes are most common in production settings, while oil-based brushable polyurethane is sometimes used by individual builders. Surface preparation is similar to other finishes: sand to 320-400 grit, fill pores if needed, and apply a compatible sealer. Catalyzed polyurethane is mixed with a hardener immediately before use and has a limited pot life (typically 2-8 hours depending on the product). The finish is sprayed with HVLP equipment in a spray booth. Fewer coats are needed compared to nitrocellulose because polyurethane builds thickness more quickly and each coat does not dissolve into the previous one. Three to five coats of clear typically provide adequate protection. Cure time depends on the formulation: catalyzed polyurethane may be ready for leveling in one to two weeks, while oil-based versi…