After purchasing a nice circa 1903 townhouse in the middle of beautiful historic Hampden in Baltimore, I discovered many things that need to be fixed before the property can be called home. Among them the most visible problem was the exposed brick wall on the first floor. Previous owner knocked down plaster that was covering the brick wall in the front and middle rooms on the first floor, but left it covered with plaster dust, with missing bricks, holes and overall completely ugly. I like the idea of exposed brick wall, but in my mind it should look bright, not dusty.
I asked every contractor I knew what to do with it, and whether they will do it, and got many answers ranging from "just wipe the dust yourself" to "I will need a lot of muriatic acid". None of them seemed very plausible. I searched the net, and found many conflicting opinions.
First thing I discovered by trial and error is that muriatic acid cannot be used on the type of brick that was in my house. This old brick will discolor and be even uglier then it was before muriatic acid treatment, but in a permanent and unrepairable way.
Second thing I tried was a rotating steel brush attachment for my drill. This did very little to the plaster dust, but left nasty black marks on the brick itself.
Third method I tried was sandblasting. I own a nice compressor, and Home Depot sells very inexpensive (~ $20) sandblasting gizmo. This was a total disaster. Sand was everywhere, and I had a hole between the bricks where old mortar used to be. Needless to say, I limited the damage to one brick, and called it a failed attempt.
One contractor suggested that he can clean the brick with power wash, and even agreed to do it for a reasonable price. However, he did not call me next week as agreed, and his phone kept ringing unanswered at first and later got disconnected.
However, he did give me the right idea. I do not own a power washing machine. I do not believe in cheap imitations that Home Depot has for $100-$200, and do not want to spend $500 for a real thing, so I figured that maybe a wet brush will do the trick. After trying several methods, me and my wife found that a brass brush does the best job. By using plenty of water and a ton of these little brass brushes (they wear down to bare plastic after a couple of hours of scraping) the entire wall was cleaned to our satisfaction. It did take a lot of time: we worked on it for a couple of hours every day, and it took over a week to complete the 9' high by 33' long wall. Ok, ok, SHE worked on it a couple of hours every day for over a week, and I mostly marveled at her resolve.
Brass brush:
Here is a section of the wall that is partially completed for comparison of how it looks before (bottom) and after (top):
Couple more pointers for the ones who might venture into this: there is a lot of dirty runoff that can be collected into a little pool made from plastic sheets sold in hardware stores as covers for painters. I have placed pieces of 2x4's on the floor in a shape of a small pool, laid a piece of plastic overlapping the "pool" and two bottom brick rows, then used cheapest, i.e. softest silicone caulk to glue plastic to the wall. Soft silicone caulk, the kind that has the least warranty (10 years is ideal if you can find it, HD only sells 30-year and 50-year kinds) peels off the brick easily once you are done cleaning the wall.
I think that power wash might be a faster way, but it will not give you the same level of detail, and it requires expensive equipment. Also, I suspect it will be much harder to contain the runoff from it.
After the wall was cleaned, I fixed all the big holes using bricks and mortar. Today's mortar looks completely different from the one that was used in Baltimore some 100 years ago. To preserve the look, I left deeper groves between bricks, and filled them with regular colored tile grout from Home Depot, that was a close color match to the old sand-colored mortar.
After cleaning and fixing the wall was sprayed heavily with liquid silicone sealer to preserve the look, and make the 100-year old mortar hold better. Some people recommended using polyurethane to coat the brick, but that gives it an unnatural shiny-glossy look that I personally do not like. Silicone sealer gives the red brick a little deeper color, but other then that is virtually undetectable. Keep in mind that the silicone sealer is 5% silicone and 95% organic solvent, so after you spray a couple of gallons of it on the wall you will end up with over 7 quarts of organic solvent evaporating rapidly. Besides an unbearable stench it is pretty hazardous to health and can easily catch fire, or worse - explode. Open as many windows as practical, and wear adequate personal protection when spraying. Leave the building as soon as possible when done, and let it ventilate for a day or until all smell is gone.
Good luck with your wall!
Some useful links:
Masonry message board: a good place to ask your questions about brick walls.
Another Masonry-related message board.