The invention relates to a kit for preparing a chromium(VI)-free slurry suspension for diffusion coating of metal surfaces, the kit comprising, as separate components, a powder mixture and a liquid binder mixture, configured to be combined for preparing the slurry suspension, wherein the powder mixture comprises a powdered diffusion metal, wherein the binder mixture comprises an aqueous solvent and a phosphate binder, and wherein both the powder mixture and the binder mixture are free of chromium(VI) salts. The invention further relates to a method of diffusion coating a metal surface using such a kit, and to the use of such a kit in various industries.