Homes have been built for hundreds of years with the knowledge that brickwork is not impervious to water. Water can migrate into brickwork. Brickwork handles this moisture by either having a cavity or separation between itself and the wall behind it or by being so thick that it acts as a barrier to the water.
For a drainage wall, water travels down the backs ide of the brick in the air space and is then channeled out with flashing (metal or plastic sheet) sloped toward the face of the wall and weep holes (small openings or tubes) spaced every few brick at the mortar joints. These flashing and weep holes should be located above all doors and windows, below all window sills, and above the ground at the base of the wall. In a barrier wall, the mass of the brickwork keeps the interior of the wall dry by allowing water to evaporate before proceeding all the way through the wall. Only under prolonged exposure to sustained moisture or rain will a barrier wall exhibit moisture on the interior. When this occurs, the moisture then drains down the back of the wall into flashing at the base which channels it out through weep holes.
The overwhelming majority of brickwork is properly detailed and constructed, experiencing no moisture problems. In the few instances where moisture is a problem, it can be attributed to poor construction or detailing in the brickwork. It is important to maintain a clean space behind the brick in drainage walls. Full contact between mortar and bricks and proper installation of flashing and weep holes are also important to ensure the highest water penetration resistance. Applying and maintaining a proper sealant around window and door openings also plays a vital role in keeping moisture out.
For additional information on water penetration resistance of brick, see Technical Notes 7, 7A and 7B.
For additional information on cleaning, see Technical Notes 20.