Shellac
Shellac is a resin dissolved in denatured alcohol. Zinsser says its shellac dries dust-free in minutes and can be recoated in under an hour, and is sold either as dry flakes you dissolve yourself or premixed in cans.
Cuts: how strong the mix is
Shellac strength is given as a "pound cut": pounds of dry flake per US gallon of alcohol. Zinsser's Bulls Eye cans are a 3 lb cut. Its data sheet says the can may be used as it comes but recommends thinning it first, and that several thin coats do better than one or two thick ones. To mix a cut from flakes or thin a can, use the shellac cut calculator.
Zinsser's cans, by their own data sheets
Dry and recoat times are at 70 °F. Each row is the maker's own figure for its own product, so a single source is the authority here.
| Product | What it is | Dry and recoat | Coverage |
|---|---|---|---|
| Bulls Eye Shellac (Clear, Amber) | Premixed 3 lb cut. Not recommended under polyurethane. | First coat on bare wood: sand and recoat in about 20–30 minutes. Later coats: touch-dry in 10–15 minutes, sand and recoat in about an hour. | About 400–600 sq ft/gal (37–55 m² per gallon) One source: Rust-Oleum (Zinsser), the maker of that product |
| Bulls Eye SealCoat | Dewaxed shellac sanding sealer, the one Zinsser names for sealing wood under polyurethane. Mixed 1:1 with denatured alcohol, it is also a pre-stain conditioner. | Sand after 45 minutes; recoat in less than an hour; let a second coat dry an hour before the finish coat. | About 400–600 sq ft/gal (9.8–14.8 m²/L) One source: Rust-Oleum (Zinsser), the maker of that product |
SealCoat's sheet also gives its volume solids, 15.5 %, and a theoretical 248 sq ft per gallon at 1 mil of dry film. That squares with the arithmetic: a gallon is 231 cubic inches, which spread 1 mil (0.001 in) thick covers 1,604 sq ft, and 15.5 % of 1,604 is 249. The practical 400–600 figure is for thinner coats.
Limits Zinsser states
- Do not apply when relative humidity is over 85 % or within 10 °F of the dew point.
- Not recommended where the surface gets hotter than 160 °F (71 °C).
- Not as durable or scratch-resistant as polyurethane or floor finishes, by Zinsser's own comparison.
- Remove any wax from the surface with mineral spirits before you start.
Shellac and food contact
The federal rule for coatings that touch food over and over, 21 CFR 175.300, lists shellac among the resins such a coating may be made from. That list is of ingredients: the rule also requires the finished coating to pass extraction limits, so an ingredient being listed does not make any particular product compliant. Zinsser describes dry Bulls Eye Shellac as "non-toxic and hypoallergenic" and suggests it for children's toys; its data sheet makes no food-contact claim. We make none of our own.
Against other finishes
Shellac side by side: shellac vs polyurethane and lacquer vs shellac. Zinsser's figures are also in the finish dry time chart and the finish coverage calculator.