Restoration of painted sandstone outer wall of tenement flat

You go to a specialist who is used to working with lime mortar, lime mortar has no cement in it and anyone who tells you different run a mile from, but painting over a lime mortar wall - unless it is a lime wash paint - does not really work as the paint stops the lime mortar from doing its job and defeats the purpose of re-pointing in the first place. Simple lime mortar for breathing, cement for sealing. Don't know where you are in the country - if you were local, would be happy to advise you. Good luck Alex