Homeowners hear a lot of strange suggestions when it comes to repairing a flashing at the bottom of a brick wall, or installing one where it had not been installed. Actually it is a bit difficult to find reliable guidance in this endeavour as most industry brick information is intended for industrial buildings, not residences. There is a lot of imformation on how to do it right, even better, during construction -- but what to do when there is a whole wall of brick sitting on the very shelf where you need to install the flashing? Simply spraying some liquid waterproofing coating through holes in the brick will certainly not insure that you effectively caught all water flowing from higher up and forced it all through the weeping holes, especially since there is quite normally some mortar spills down in the bottom of that air space between the brick and the house.
First a little building science to understand why we need flashing and weep holes in the wall in the first place. Essentially it should never be assumed that any siding will be forever perfectly resistant to water -- it is far better to build with a design that accepts that the siding on the wall will shed most water, but not all of it, and then there are provisions behind that siding to prevent water from getting into the stud walls and drainage provisions to allow it to escape outward at the bottom of the wall. Click on this link to see an animation on just what is a Rain Screen wall. Then clic on this link for some details on the weeping holes in a brick wall. And for those of you who are really technically oriented, here is some detailing of Rainscreen construction in the Canadian climate.
Finding retrofit information was a lot more difficult than finding Best Practices. After considerable searching I was led to The Brick Industry Association of the US, one of the few associations who still have a series of publically available Technical Notes on Brick Construction at www.GoBrick.com. Tec Note #46 Maintenance of Brick Masonry details two techniques for actually removing bricks, installing the flashing and putting the bricks back into place - as shown in the photos above. I wanted to guide you to this authorative PDF so that homeowners could discuss the task intelligently with a contractor, perhaps even supply the information to a contractor who was not sure of how to proceed.