I worked for a masonry company and one day I over heard one of the guys I worked with ask the boss about washing the brick. I asked him about it and he said he would pay me $20 an hour to help. I went for it and decided it was something I liked doing and could make good money at. I first started out washing brick with a bucket and brush but quickly turned to washing with a pressure washer. I easily get $0.45 a sq ft. You can wash 250 sq ft an hour pretty easy. That is $112 an hour.
It is hard to get masonry companies to let you do it though. When you wash a house and ruin their siding they can replace it for under $10,000. If you ruin brick it can cost half a million or more to replace. That would be commercial brick of course i.e. schools, offices, stores. I can get the jobs easier becuse I know the ins and outs of masonry and that makes them more comfortable.