What angle did you spray against the brick with the pressure washer?

I have one that will carve concrete if you get the nozzle close and at 90 degrees to the surface.

Use it at a shallow angle (less than 45 degrees) and it cleans with no damage.

I do know you can clean paint off of brick. I've seen it done here in town on a three story building that was covered in layers of paint. The guy did not use a pressure washer the brick was too old for it. He did end up putting a protective seal on it when it was done.
I'd call a brick mason and ask if you aren't getting the results you want with the pressure washer.

i was watching hgtv and they were cleaning a brick fireplace...with like scrubing bubbles just saw that today!
hope this helps you

hi, just came by this thread by accident...

saw your picture and it looks to me like the white chalky paint residue may be efflorescence: the lime in the brick and mortar leaking out where moisture has built up behind. this is pretty common, esp with old homes where there are no weep holes. maybe get a local inspector's opinion, 'cause you may be washing it a few times only to have it come back.
it could also be that your sills have no drip edge which means water capillaries back against the brick right under the sills, and stays long enough to force out the lime, and, more importantly, weaken the brick face... which is why power-washing it may cause it to spall off. i hope the black is just soot, which can probably be washed off somehow, and not mildew, which may be symptomatic of built-up moisture behind...

anyhow, just my two cents based on a photo. sorry, shouldn't give an architect's advice based on just that, so again i'd suggest getting a local pro opinion.

good luck!

It's good that you mention it may be something other than paint, but I am suspicious it is from the painting. There was a beautiful old Victorian across the street from my parent's house in town. There was no indication of any white under the windows on this brick house for decades, until the property changed hands and the new owners painted all the stone sills with what was likely a very cheap latex white paint.

It was only after this time did the white ghost like smudges appear under all the windows in the old soft brick house, like chalk water had seeped along the face of the brick by capillary action. Could have been a coincidence and would have happened anyway, but thought it suspicious that it happened to all the windows, on all exposures of the house at the same time. That doesn't make sense.

The stone window sills on our house were painted and we used PeelAway 1 to remove the paint. Then we used a concrete cleaner which we purchased at Ace and we scrubbed. This cleaner came in a white plastic bottle with green writing. Do you have smooth brick or bumpy brick? I hope you have smooth - it's easier to clean that way.

Another suggestion is to check with your local brickyard and ask them if they recommend any particular products for cleaning brick. When we lived in St. Paul, MN, we got a referral for a product (whose name I can't remember now) that can be used for cleaning graffiti. It was expensive and that's why we tried the PeelAway and Ace Hardware cleaner first.