Zinc carbonates such as carbonic acid zinc salt, zinc carbonate hydroxide monohydrate, zinc bicarbonate, zinc tetraamine carbonate, zinc ammonium carbonate, carbamic acid zinc salt and zinc carbamate can initiate hardening of polyurethane coatings and decrease the coating tack-free time. The decreased tack-free times facilitate earlier application of additional polyurethane layers and earlier return of a coated article to service, and can provide improved floor finishes.