Spraying aerosol finishes

Overview

Aerosol cans put sanding sealers, shellac, lacquer and polyurethane on wood with no gun to buy or clean. Fine Woodworking's Mark Schofield calls them a simple, economical way to get a smooth finish and says most cost well under $20. Woodsmith's Ted Raife offers the central rule: treat the can like a spray gun, with consistent distance, steady movement, overlapping passes and several thin coats.

When to use

• Boxes, small hanging cabinets, turnings, carvings, frames and parts with lots of corners.
• Touch-ups, specialty coatings (brass lacquer, toners) and rare colours; Woodworker's Journal (Dresdner) notes these are often only sold in cans.
• Not for large work. Schofield's example is a four-foot chest: strips of finish dry before the next strip blends. Cost also rises quickly on big pieces, since you pay for the propellant and overspray (Woodsmith). For those, see Spraying with HVLP or Wipe-on application.

Materials and tools

• The aerosol finish. Most categories are available: Shellac, Nitrocellulose lacquer, Pre-catalyzed and post-catalyzed lacquer and oil-based polyurethane (Dresdner). Match sheen and type to your project; see Sheen control and matching.
• Spare tips: Dresdner notes Mohawk sold 16 replaceable tips for different fan shapes, about 25 cents each, as a cure for clogging.
• Scrap board to test on; kraft paper to catch overspray.

Steps

1. Prepare the surface fully; spray exposes scratches (Woodsmith). Remove dust.
2. Seal first if the wood is thirsty. Dresdner says aerosols are often around 6% solids, so the first coats soak into end grain and soft woods; flood on Dewaxed shellac, wipe off the excess, and the sprayed coats build faster. See also Finishing end grain.
3. Plan to spray interiors and hidden faces first, the prominent faces last.
4. Shake for the label time. For rattle-ball cans Dresdner says keep shaking for a full 60 seconds after you hear the ball moving.
5. Test on scrap for fan width and speed.
6. Hold the can parallel to the work at the distance printed on the can (Dresdner: 6 to 8 in; Woodsmith: about 10 to 12 in is common). Follow the label.
7. Start spraying beyond one edge, move the whole arm parallel (do not swing in an arc), and release past the opposite edge. Never stop over the work: it sags.
8. Overlap about half a pattern on the first coat. Wet but not dripping.
9. Several thin coats beat one heavy one. Follow the label's recoat time, and let the first coats dry longer before a light sanding (Woodsmith). When done, invert the can and spray until only gas comes out to clear the tip.

Common problems

• Runs and sags: too close, too slow or too heavy; see Troubleshooting finish defects.
• Visible strips on big flat surfaces: finish dried between passes. Use a gun.
• Uneven sheen: mixing different coats or cans; build all coats the same.
• Blush on humid days: see Curing conditions and time-to-use.

Safety and environment

Cans make overspray and vapour. Woodsmith advises spraying away from open shop air, or outdoors when the label allows, in shelter from wind and dust. Follow the label for ventilation and respirator, and keep vapour away from flames, sparks and heaters. See Oily rag safety for rag disposal.

Related

• Spraying with HVLP: guns for larger work.
• Rubbing out a finish: levelling the final film.
• Repairing finish damage: aerosol touch-up lacquers.