What are the best practical ways to prevent mortar droppings from filling the air space in cavity walls and blocking weep holes at the bottom of the cavity?
- Several methods are used. Mortar on bed joints can be sloped downward towards the back of the joint (see figure, below). This reduces the amount of mortar that protrudes into the cavity and therefore reduces or eliminates mortar droppings. The Brick Institute of America further recommends using pea gravel at the base of the cavity to prevent blockage of weep holes. However, I prefer installing a 16- or 24-inch-high strip of drainage mat along the bottom of the cavity. This performs the same function and is less likely to damage flashing. Cut slits in the drainage mat to extend wall ties through. The drainage mat creates a vertical plane that is free of mortar droppings, but does not eliminate the need to keep cavities clean. Excessive mortar droppings may still bridge the cavity and cause problems.Some architects recommend using a board with two wires attached to collect mortar droppings. The board is lifted out of the cavity and cleaned before installing the next row of ties. The board is then placed on top of the new ties and construction continues.