While water leakage does not relate directly to air-tightness and thermal performance, the
interactions between the elements intended to control water and those intended to control air
leakage and heat transfer must be addressed. Also, water leakage can lead to the deterioration of
the elements controlling air leakage and heat loss.
Rain penetrates masonry walls through cracks at mortar-unit interfaces, unfilled mortar joints,
movement and shrinkage cracks, and interfaces of the masonry wall with other wall components.
The impact of raindrops directly on cracks is not a major contributor to water leakage, rather water
running down the face of the masonry leaks through cracks due to capillary action and air pressures
across the wall. Gravity can also be an important factor in larger openings that slant inwards. It is
important to keep water off the wall through the use of properly designed drips on copings, ledges,
sills and balconies, because any wall will leak if it is continuously flooded with water.
For a solid masonry wall, or any masonry wythe, to be watertight the masonry units and mortar
must be compatible, the mortar joints must be completely filled and properly tooled, and the wall
must be sufficiently thick. Compatibility between the units and mortar is necessary to achieve a
good bond, otherwise there will be unbonded areas and cracks will be more likely to develop. In
addition, the mortar joints need to be properly tooled in order to compact the mortar against the
units and to close capillary cracks. If a masonry wall is sufficiently thick, then the water that does
penetrate the facade will generally not reach the interior face before it is able to dry out. This is the
approach that controlled rain penetration in older masonry construction, and it worked well in these
very thick walls. In modern construction, masonry walls are generally not load-bearing and are
therefore thinner and less forgiving of water leakage. In order to control water leakage in modern,
masonry walls, industry guidance on mortar and joint tooling should be followed, but given the miles
of mortar-unit interface it is unrealistic to expect to be able control all of the water leakage.
Therefore, good masonry construction for rain penetration should be supplemented by the use of a
facade or veneer that provides a second line of defense combined with a drainage system to
remove the water that penetrates the facade. Design for the control of water leakage requires an
understanding of how the cavity wall system is supposed to perform plus achieving the following
key performance elements: the brick veneer should be as watertight as possible, flashing must be
properly installed at all required locations, the cavity must be well drained and the backup wall must
be airtight and watertight.
ASTM E 514 provides a test method for determining a masonry wall's resistance to water
penetration subject to wind driven rain. This procedure involves a wall installed in a test chamber,
as opposed to a field test.