There is a fool running around Victoria with a sand blaster who has talked several building owners into giving their building a "face lift." Dirt and mildew often darken the surface of older, porous bricks. There are vavious soaps, bleaches and coatings that can help with this benign problem.
An extreme response would be a thorough power washing.
This guy has stepped it up a notch. He blasts away up to 1/4 inch of the brick's surface, removing the hardest most weather resistent layer and leaving a soft, chalky, pock marked surface that is bound to absorb every drop of rain that hits it. It's the equivalent of 200 or 300 hundred years worth of surface erosion in one day. I have recycled 150 yr old bricks which still have their original surface largely intact. The sand blasted bricks are so badly damaged that they may need to be stuccoed over to prevent spalling.
Hopefully this guy will damage a building on the heritage registry and be shut down by the cost of fines. Some sort of ladder or scaffold failure would serve the common good in his case.
I have seen that done to the INSIDE of a building, but never the outside. That case was a last resort to remove some grafiti that permanently stained the brickface.
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi.
"Family farms work when the whole family works the farm." -- Adam Klaus
The Greenhouse of the Future ebook by Francis Gendron