Tried acid before mate.. thats all we used in London for years, if its been there a while, its a nightmare to get out...
Although you are right, it does work and thats what all rust removers have in them, the hydrochloric, but ive had very mixed results...some vanishes with acid, some takes a few coats, and some doesnt budge.. i just get the wetblaster out now mate, little bit of sand and 2 mins and its gone..