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Water penetration
Together with differential and restricted movement, water penetration is responsible for most of the problems encountered in walls today. Once a wall is saturated with water, freezing and thawing cycles will likely cause cracking, crazing, spalling, delamination, and ultimately disintegration. Water can in turn cause major movement and dimensional changes. Added to these, it will facilitate metal corrosion, lose of insulation effectiveness, deteriorate interior finishes, faciltate the development of fungi and molds, deteriorate indoor air quality, and enable leaching and efflorescence to appear on exterior or even interior surfaces.
Water sources
At least some amounts of water are always available in construction
projects. Rain and snow wet building components, and so does
condensation. Regardless of the source, water vapor is omni-present
in the surrounding air. It is safe to state that for common
construction water cannot be completely eliminated; therefore the
solution is to control water penetration.
Water generally penetrates brick walls through openings such as
cracks, delaminations and minute separations between the brick units
and the mortar joints, as well as faults around building openings and
various types of joints. The other necessary factor for water
penetration is the presence of forces to either push or draw the
water through.
Under normal conditions, it is virtually
impossible for any significant amounts of water to pass directly
through the brick units or through the complete mortar joints
(though incompletely filled mortar joints are another story). While
most brick is absorbent, the amount of water it will absorb is
relatively small, so it is unlikely to contribute to an outright
flow of water through a wall. Same can be said about the mortar
joints, as long as the mortar covers monolithically the whole depth
of the brick.
Masonry walls
Historically masonry walls functioned as both the structural system and as the exterior skin of the building for most of the human history since antiquity. As a result, these masonry walls were quite massive, ranging in thickness from 12 in. (300 mm) up to 6 ft (1.80 m) of solid brick. These masonry walls, both because of their thickness and their being in quasi-constant compression due to the structural loads, worked quite well in keeping water out. Their other major advantage was that they offered a large thermal mass which kept movement from temperature changes to a minimum. Many older masonry walls were built with cornices and other ornamentation which also protected the facades of the buildings from excessive water rundown and subsequent water penetration.
Contemorary walls
Walls used today are much less massive, and the masonry veneer may be only 3-3.5 in. (75-90 mm) in thickness. In many cases, they have no overhang at the top, allowing sheeting of the rain water from the roof or parapet down to the ground. As a result of these newer wall systems, rain water is allowed to be in contact with the masonry in larger quantities and for longer periods of time, thus leading to more opportunity for water penetration problems.
Mitigating the problem
The successful performance of a masonry wall depends on limiting the
amount of water penetration and controlling any water that enters
the wall system. This means at the very least controlling the amount,
size, widths, and location of building envelope cracks, as well as
diverting rain water rapidly effectively. Other water ingress
sources such as ineffective sills, caps or copings have to be
considered as well. If water penetration can be limited, and
effectively drained once penetration occured, for all practical
purposes the wall will remain dry.
