Abstract: A method of controlling the final coating thickness of a diffused aluminide coating on a metal substrate. The method includes: (a) depositing an alumina-doped platinum-silicon powder onto a metal substrate, (b) heating the coated substrate to diffuse the platinum-silicon powder into the substrate and removing the undiffused scale, (c) depositing an aluminum-bearing powder onto the platinum-silicon-enriched substrate, and (d) heating the coated substrate to diffuse the aluminum-bearing powder into the substrate and removing the undiffused scale. The depositions are preferably done electrophoretically, in which case the Pt--Si deposition bath is doped with alumina or some other inert particulate. Alternatively, slurry deposition may be used. The method may also be used to deposit Pd--Si coatings onto metal substrates.