Weep holes may seem a small part of masonry wall construction, but they are critical to the durability and performance of cavity walls. Weep holes should be installed in the masonry head joints above all flashing courses. This includes the base of the wall, above all window and door lintels, and above shelf angles. Anywhere the cavity is interrupted, you must install flashing and weeps. There are several ways to form weep holes. Each type has a different appearance as well as advantages and disadvantages.
OPEN HEAD JOINTS
The most common type is the open head joint. Open head joints are easy to form. Mortar is left out of the joint, leaving an open channel that is 3/8 inch wide by course height by veneer depth.
Hollow plastic tubes also are used to form weep holes. The most common ones are 1/4 or 3/8 inch in diameter by 3 1/2 to 4 inches long. Manufacturers recommend installing them at an angle in the mortar of the head joints, spaced 16 inches apart.
Cotton wicks are used to form another type of weep system. A 1/4 to 3/8 inch diameter rope is installed in joints at 16 inches on center. The rope should be 10 to 12 inches long and extend through the veneer face and up into the cavity wall above the height of any possible mortar droppings. Moisture in the cavity is absorbed by the cotton material and wicked to the outside face of the wall where it evaporates.
OILED RODS OR ROPES
Another alternative for cavity wall drainage are oiled rods or ropes mortared into bed joints 16 inches apart and then removed when the mortar has set. The rods function much the same as plastic tube weep holes.