We’ve seen brick that are always in the shade under a tree or shrub canopy or along an alleyway and has a dirty gritty buildup on some or all of the wall. Sometimes a pressure washer is the perfect tool to clean this off. The brick should be in good condition though. If it’s old and the mortar is getting soft, then you have to be really careful.
If you have to wash a wall, then don’t do it on a very hot day when the wall is in full sun because this is an unnecessary “shock” to the brick/mortar composite. The cold water on hot brick could cause loss of bond that may show up at some point in the future.
If you’re washing off efflorescence, then make sure that the wall dries out completely (this may take several days) before applying Siloxane.
