Mold is the American spelling for all senses of the word meaning, among other things, (1) a frame for shaping something, (2) to shape in a mold, and (3) any of various fungi that commonly grow on organic matter and are often associated with decay. Mould is the British spelling. American English has no mould, and British English has no mold.
Australian and Canadian English favor the British spelling, though mold is fairly common in Canadian publications.
Examples
These American publications use mold for all senses of the word:
Inside, the rain had spawned black, green, and yellow mold that crawled the walls. [Atlantic]
Obama has been more in the mold of George H.W. Bush and his secretary of state … [Daily Beast]
If some of the insulation is intact, leave it in place unless it is moldy. [Boston Globe]
Outside the U.S., mould is the preferred spelling—for example:
Without air conditioning in a highly humid climate, mould could form. [Montreal Gazette]
And Pretty Ballerinas is still making shoes in the mould of the original pair created in 1918. [New Zealand Herald]
There’s no bread, and even the mouldy cheese has been chipped away at … [Scotsman]
