All brick walls, old and new, are susceptible to deterioration. Exposure to harsh weather, poor construction, and lack of maintenance can all lead to the failure of brick structures.
The key to maintaining a healthy brick wall is being able to read the distress signs and diagnose problem areas before they turn into a serious issue, says building restoration expert K. Nam Shiu, P.E., S.E., VP with Walker Restoration Consultants, based in the firm's Elgin, Ill., office.
To help AEC professionals and building owners identify problems before they get serious, Shiu offers four key indicators of an unhealthy brick wall system.
1. The masonry wall is bowed, especially at the parapet level.
Shiu says bowing is typically caused by the expansion of the bricks as they absorb moisture over time.
“Clay-fired brick comes from a kiln completely dried out, and it has a tendency to expand in length as it absorbs moisture over time,” says Shiu.
Without proper expansion joints, a brick wall will continue to expand, placing considerable pressure on the corners of the walls. Some older buildings do not have expansion joints large enough to accommodate that movement, and the expanding bricks start to push the corner, says Shiu.
“Because the corners are stiffer than the middle of the wall, the only direction the wall can move is outward or inward, resulting in a bowed effect,” says Shiu, adding that expansion is particularly troublesome at the parapet level because the bricks are exposed to the weather on both sides.
Bowing can even occur with new construction, particularly when it combines concrete framing and brick veneer.
“This situation can create an even bigger problem because concrete tends to shorten and shrink over time, while the brick does the opposite,” says Shiu. “If you're going to mix and match materials, make sure to incorporate relief joints.”
If the pressure is not relieved, the expanding wall can eventually cause the corners to crack. “At that time, you'll need to do some repair,” says Shiu. “We'll typically tuck-point the corner and cut a relief joint to accommodate further movement.”
For incidents where the expansion is so severe that it dislodges bricks, Shiu recommends that the brick wall be dismantled and rebuilt with proper relief joints.
2. Portions of the brick are covered with a white powdery substance.
This phenomenon is known as efflorescence, and it is commonly caused by excessive moisture build-up in the brick wall over a long period of time.
“It's a sign that the wall is not drying properly,” says Shiu.
Here's how efflorescence occurs: The moisture inside the brick carries soluble salt or dissolves salt from surrounding mortar. As the salt-laden moisture moves to the outer surface and evaporates, the salt is left behind in the form of a white powder deposit.
Shiu says the powder itself does not cause harm to the brick wall. Rather, it serves as an indication that the wall system is not drying properly.
“The most common cause of efflorescence is having the drainage cavity clogged by debris or mortar droppings,” says Shiu. “I've seen walls where the cavity at the bottom course of brick was completely filled with mortar, which allows water to soak in for a longer period of time.”
Other common causes include faulty copings and flashings and leaking pipes.
3. Diagonal cracking, especially at the corners of windows, and sagging in the middle of the window headers.
Cracking and outward bowing can be caused by any number of problems (including those discussed in #2), but a common culprit with brick veneer wall systems is the deterioration of the supporting shelf angles. These steel elements are commonly found at every floor and over the window headers. They are generally attached to the concrete frame, offering support to the brick veneer, or spanned between the window jambs over the window openings to support the window headers.
Shelf angles typically fail in one of two ways: when exposed to excessive moisture, the shelf angles can corrode and suffer loss of cross-sectional areas; or, as the brick wall expands vertically, the angles can be completely dislodged from the concrete frame due to the differential vertical movements between the brick veneer and the building frame.
“What eventually happens is the angle is pushed up to a point where it breaks or fractures the bolts that tie the angles to the concrete slab edges,” says Shiu.
Either way, when shelf angles at the floor levels fail, it places immense pressure on the veneer wall system.
“When a brick façade loses its floor level support, it will begin to rest on the brick below,” says Shiu. “At the same time, the wall will continue to elongate, placing more pressure on the system and causing cracking and outward bowing. That becomes a very dangerous situation when you factor in the wind load. As a result, the entire brick wall can come off the building abruptly during a wind storm.”
Shiu recommends using galvanized steel angles instead of unprotected steel. Also, make sure to incorporate appropriate soft joints to allow for the differential movement between the brick veneer wall and the building frame system. Finally, consider including special details to keep the shelf angles dry, such as plastic flashing on top of the shelf angles.
4. Portions of the mortar joints are missing or deteriorating.
Mortar joints are designed to be weaker than the brick blocks, and therefore will wear and break over time. Shiu says with normal aging of brick walls, building owners should anticipate tuck-pointing to repair mortar joints after 15-20 years.
“A common problem is when the mortar actually becomes stronger than the brick itself,” says Shiu. “With the common use of portland cement, mortar has become stronger and more impervious to water.” This can lead to spalling of brick edges and can trap moisture behind the veneer, thereby promoting corrosion of the steel shelf angles and lateral ties.
