down the street from me is a huge manufacturing plant. it is 3/4 brick up the walls and the remaining 1/4 is a corregated metal.
I was asked to bid on painting this metal strip. It was about 150 yards long and the job actually entailed masking off the brick area and spraying the metal. My bid was too high, so they said, because of the labor in masking. they wanted a cheap job for cheap money and said to forget the masking just use a spray shield the best you can. This did not settle with me. I was then glad I lost the bid.
anyway, another contractor got the job and they did not use masking paper or a shield and the overspray just ruined the brick about 1 foot downfrom the metal.
This contractor was out there one day with a power sprayer, no good, then a crew with wire brushes, no good, then one day with a small portable sand blaster and no good. I then guess the contractor left town.
Just goes to show you.
In answer, getting paint off brick, esp the porus brick is one big job.