idioms

[fatzo]

Hello
Does someone know the equivalent in english of the following French idiomatic expressions? precher dans le desert and broyer du vent. Thank you

 

[chrisdev]

We've got the expression, 'You're wasting your breath' meaning it is pointless to continue speaking because noone is really listening.
There's another expression 'It's like banging your head against a brick wall' which means it doesn't matter how many times you explain something, your listener is never going to understand you or to listen.
These don't exactly catch the sense of the French idioms, though. Maybe another teacher / native speaker can think of some more...