FYI it's a somewhat regional or (in the UK) class stratified grammar distinction.
While nobody would say "fewer sand", "less" is in practice often used by native English speakers for both count and non-count nouns so it's not really wrong so much as it is revealing.
While nobody would say "fewer sand", "less" is in practice often used by native English speakers for both count and non-count nouns so it's not really wrong so much as it is revealing.