I agree with what has been said so far about using bleach. I would go further by saying add some soap to the mixture so it will stick better on the brick. My procedure would be:
Do a test strip first.
Wet the wall to see how fast it dries....if fast do little sections at a time....if not do one whole side
Mixture:
3 gallons bleach at 5.95%
1 quart of Tide liquid detergent
Apply with 20% draw on a downstream
Apply mixture from bottom to top
Let dwell until almost dry no more than 10 minutes
Rinse with low pressure...around 100-200psi...just back off the wall
Use plenty of water to rinse
Reapply mixture if the wall still needs more cleaning...do NOT get tempted to use higher pressure to get it off...you WILL mess up the brick that way.
GOOD LUCK!
Dennis
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Dennis A. Cormier and Gloria A. Wagner
North Georgia Spray Masters, Inc.
spraymasters@hotmail.com