Depending on surface you could try Brick Acid (Hydrochloric Acid) diluted about 4:1 with water.
If you are happy that the surface can be cleaned using acid then proceed as follows: -
Soak the surface with water, apply the acid solution via brush or sprayer, leave for a couple of minutes then rinse. Repeat as required and extend the amount of 'dwell' time each time you do this.