Many architects recommend that no mortar be used for the brick course that is directly on the flashing over a shelf angle. If mortar is not used on the flashing, what keeps the brick from sliding off the angle?

When mortar is placed on flashings on foundations, it is normally used to level the lowest course. Even if the flashing is bonded to the shelf angle, the mortar does not bond well to either plastic or metal flashing.

After the masonry wall is installed and the mortar cured, the wall above the shelf angle acts as one rigid element. Because the exterior wythe is anchored to the backup with many ties, the wall is prevented from moving laterally. The shelf angle is not intended to provide lateral support, but instead its purpose is to create vertical support. The first tie is generally located at a height above the shelf angle equal to half the typical tie spacing. This placement provides sufficient lateral restraint at the lower portion of the wall.

Some friction occurs between the brick and flashing; however, this action is generally not relied on to provide resistance for lateral loads. As long as the shelf angle supports at least two-thirds of the wall width, the wall should be stable during construction as well.

I typically do not recommend using mortar on the top surface of the flashing since it slows down drainage of water from the wall. Without mortar, water drains not only at the weeps, but also along the entire length of the flashing.

At shelf angles, laying brick dry on the flashing helps the coursing stay closer to uniform since the angle and joint beneath the angle is already greater than the typical mortar joints. The illustration shows this arrangement.