Nitrocellulose lacquer

Overview

Nitrocellulose lacquer is a solvent-borne film that dries only by evaporation. It displaced shellac as the main factory furniture finish in the 1920s and 1930s (Wikipedia) and is still a standard spray finish because it dries in minutes, rubs out to a good sheen, and can be repaired by re-dissolving. It is a moderate-durability film, and it is made with very flammable solvents.

Pros

• Very fast: Mohawk's Finisher's Choice is touch dry in 7 minutes and recoats in 45 minutes (manufacturer data sheet).
• Each coat dissolves into the last, so there is no hard recoat window; the EPA defines lacquer as drying "by evaporation without chemical reaction" (40 CFR 59.402).
• Reversible with solvent, easy to touch up and to rub out (Rubbing out a finish).
• Can be polished to a high sheen; Wikipedia's Lacquer article calls the film "hard yet flexible, durable".
• Mohawk sells 275 g/L and 550 g/L VOC versions of the same product family.

Cons

• Highly flammable material (Wikipedia on nitrocellulose); the Mohawk data sheet lists a flash point of -4 F, and the SDS lists acetone at 60 to 80%.
• Sources differ on hardness: Wikipedia's Lacquer article says hard yet flexible, while its wood-finishing comparison table says soft, somewhat durable, reasonable protection. Mohawk markets its DuraCoat pre-cat as "greater durability compared to regular nitrocellulose lacquers". See Pre-catalyzed and post-catalyzed lacquer and Conversion varnish.
• Low solids (about 14% by volume for Finisher's Choice) means many coats for build.
• Needs spray gear and a booth for best results; brush-on consumer lacquers are a different, slower-flashing formulation.
• Federal VOC limit for lacquers is 680 g/L (40 CFR 59), a national figure.

Suitability

Excellent for furniture, instruments and interior casework, on open-pored hardwoods such as Red oak and White oak after a Grain filler (pore filler), and on close-grained hardwoods such as Hard maple and Pecan. Not recommended for outdoor use, heavy-wear floors or bar tops. Minwax's label says not to apply its brushing lacquer over polyurethane.

Coats and application

Sand to 180 to 220 grit (Sanding schedule), dye if wished, seal with Sanding sealer (and vinyl sealer) or Dewaxed shellac, then spray (Spraying with HVLP). Mohawk's data sheet allows up to 20% retarder and says to scuff-sand aggressively with 320 between coats; keep total film to about 4 dry mils. Example: one sealer coat, sand 320, then two to three coats at about 15 to 45 minutes apart, cure, and rub out. Minwax brushing lacquer: three coats at 2 hours apart, with at least 24 hours before normal use (manufacturer). Wikipedia's table says no sanding is needed between coats; follow the maker's sheet, which for Mohawk says to scuff.

Compatibility

• Goes over Dewaxed shellac, sanding sealers, most dye and pigment stains once dry.
• Not over Oil-based polyurethane: Minwax's brushing-lacquer label says not to apply lacquer over polyurethane finishes.
• Not compatible in one film with waterborne products; keep Water-based lacquer separate.
• Fisheye from silicone polish: wipe and test.

Care and repair

Clean with a damp cloth. Surface wear can be re-sprayed because new coats burn into old ones; scratches are often rubbed out or touched up with lacquer. Strip with lacquer thinner.

Safety and environment

Extremely flammable: no flame, pilot lights or sparks. Use a NIOSH-approved respirator and ventilate; Minwax's label lists acetates, alcohols and ketones and flash-fire risk. Wikipedia describes the solvents as toxic. Wikipedia says lacquer becomes relatively non-toxic about a month after application, once solvents have left; no food-contact claim is made here. Check the SDS for the can in hand.

Related

• Pre-catalyzed and post-catalyzed lacquer: harder lacquer with an added catalyst
• CAB-acrylic lacquer: non-yellowing alternative
• Water-based lacquer: low-VOC option
• Shellac and Dewaxed shellac: the earlier finish and the usual sealer
• Spraying with HVLP, Rubbing out a finish: technique