How to clean mortar from sandstone - Unsightly mortar stins

[willz]

having tried the wire brush method,my new method of removing stains is to prewet the sandstone and then use a piece of sandpaper and get rubbing!
This has left no visible marks on my paving, as its only sand rubbing against sand

[lutonlagerlout]

if i do get a splash of the wet stuff on the flags i wash it off immediately with clean water
leaving muck stains till tomorrow is asking for trouble
LLL