Masonry Magazine October 1980 Page. 19
Type of Construction
Improperly detailed flashing, weepholes, movements joints, ties and anchors, and projections of floor slabs to the outside face of the veneer, all may lead to water penetration problems.
Clear Coatings. Other problems have occurred due to the misconception that clear coatings for brick masonry walls, such as silicones, are cure alls. This is not true. In many instances, clear coatings trap moisture or salts present in the wall and lead to spalling of the brick faces, see Technical Notes 7E.
Recommendations
# Materials
Brick-Due to the thermal isolation of the exterior brick veneer, brick or hollow brick must conform to the requirements for Grade SW in ASTM C 62, C 216, or C 652. Used, or salvaged, brick should not be permitted.
Mortar-In order to assure good bond between the mortar and brick, only portland cement-lime mortars are recommended. When wind loads are greater than 25 psf (1.2 kPa), Type S mortar should be used to obtain the maximum tensile strength. In all other cases, Type N may be used.
# Details
Airspace-In order to help the brick veneer act as a drainage type wall system, the airspace between the back of the brick and the face of the rigid sheathing must be a minimum 1 in. (25 mm). However, due to the end conditions of the ties, and the lack of research, it is recommended that the airspace not exceed 2 in. (50 mm) in width. Regardless of the exact dimension of the airspace, it is vital that it be kept clean of mortar droppings and other foreign materials. If mortar falls into the airspace, it may form "bridges" for moisture passage, or it may fall to the flashing, blocking the weepholes.
Flashing and Weepholes Flashing is installed in masonry construction to divert moisture, which may enter the masonry at vulnerable spots, to the outside. In areas of severe or moderate exposures, flashing for brick veneer should be provided at horizontal surfaces, such as roof and parapet; at shelf angles; at all openings, such as doors and windows; at floor lines, depending on the type of construction; and at the bottom of the wall just above grade, see Figs. 3, 5 and 11.
To be most effective, the flashing should extend through the outer face of the wall and turn down to form a drip. Weepholes should be provided at all flashing locations at intervals of 16 in. (400 mm) to 24 in. (600 mm) maximum, to permit water accumulated on the flashing to drain to the outside.
If, for esthetic reasons, it is necessary to conceal the flashing, the number and spacing of weepholes are even more important. In this case, the spacing should not exceed 16 in. (500 mm) o.c. Concealed flashing with tooled mortar joints can retain water in the wall for long periods of time, thus concentrating the moisture at one spot.
To prevent any possible moisture infiltration and to promote proper drainage, place the bottom of the veneer wall above the finish grade. Avoid placing earth over the weepholes during landscaping. With basement construction, it is important to use through-the-wall flashing at the bottom of the airspace to prevent moisture from penetrating the inside surface of the basement wall.
Flashing material is generally formed from sheet metals, bituminous membranes, vinyls, or combinations. The selection is largely determined by cost and suitability. Acceptable bituminous membranes do nor include asphalt impregnated felt. The cost of flashing materials varies widely. It is suggested, however, that only superior materials be selected, since replacement in the event of failure will be exceedingly expensive. For a more complete discussion of the various types of flashing available, see Technical Notes 7A.
Weepholes are formed by inserting a material into the mortar joint or by omitting mortar from all or part of a head joint. The forming material may be removed to leave an unobstructed opening, as when oiled metal rods are used, or may be left in place, as when plastic tubing or rope wicks are used. Sometimes metal screening, fibrous glass or other materials are placed in open weepholes, but this should not be done indiscriminately. Materials such as metal screening can rust and cause staining of the masonry. Some materials in weepholes, such as cotton sash cord, or nylon rope, act as wicks, drawing moisture out of the airspace.
Workmanship. The importance of the workmanship used in constructing masonry has been stressed by many, sometimes to the point that it may appear that workmanship alone is responsible for the performance of masonry walls, regardless of the wall design, detailing, or the materials used. While this is by no means true, good workmanship is a very important factor in the construction of high performance masonry.