Brick is a durable material for masonry walls that, if constructed properly and maintained, can last as long as the lifespan of the building.However, poor construction practices can lead to defects in the form of cracking, efflorescence and spalling, and defects can happen to both old and new construction. Fortunately, visual assessments of brick walls can provide valuable preliminary information regarding the integrity of the masonry and the structure behind it. This paper will discuss the characteristics of brick, typical defect patterns, and their causes.A stair-step crack is a diagonal crack but,since mortar is usually not as strong as concrete block or brick, the crack migrates to the mortar joints as it zigzags along a path of least resistance.Sometimes a stair-step crack will mostly follow themortar joints, then take a short-cut through a defective block or brick, before returning to the stair-step pattern. The crack can be caused mainly of salt applied during freezing time,shifting of the ground,not the inside right structure etc.
- Characteristics of Brick
Brick, as a material, expands naturally over the course of time. Taken directly from the kiln and placed in a controlled environment without fluctuations in moisture and temperature, test bricks were found to expand the most during the first month of installation,followed by a consistent rate of approximately .0006% per year after five years (Ref. 5). In addition, brick expands and contracts with changes in thermal temperatures and moisture.The following items will greatly influence the amount of dimensional change that a brick, and the brick wall assembly, will experience over its useful service life: The type of clay used for the brick. Manufacturers should be able to provide the coefficient of expansion for their products.The location of the brick wall. Orientation and exposure of brick walls in relation to cardinal directions will affect the amount of sunlight (heat) that will be absorbed by the wall. Walls exposed to the outdoors have a greater chance of thermal expansion and contraction, and retainage of moisture, than walls located indoors or in protected areas. Moisture retainage. Brick walls are porous, and will absorb moisture through both the bricks and the mortar joints. Unlike thermal expansion and contraction, dimensional changes in brick due to moisture are irreversible. Brick walls are relatively rigid in comparison to the overall building which moves due to a number of factors. Dimensional changes to walls due to the clay materials used, thermal variations, moisture retainage, and the ability for the wall to move with or independently from the structure, requires careful design and installation. Expansion and control joints, separation joints between dissimilar materials, and special anchoring systems provide mechanisms to prevent brick wall defects due to expansion, contraction, and minor building movement. Additionally, masonry walls should include a system of drainage space, flashing, and weep drains to direct water that penetrates through the face of the brick to the exterior.
There are different cracking patterns that can occur in brick walls. The age of the building and its construction type, such as being a cavity or mass masonry wall, wood frame, concrete frame, or steel frame structure, will aid in the diagnosis of causes for the brick cracks. The list below describes several common cracking patterns and the causes of the cracks: Vertical Cracking at Inside Building Corners: Vertical cracks at inside corners often result from thermal expansion of the adjoining walls towards each other. This type of cracking typically indicates that expansion provisions were not provided during construction of the building. Vertical Cracking at Outside Building Corners and Horizontal Cracking at Floor Lines: Typical to older mass masonry construction, vertical cracks at outside corners are indicative of structural movement. In older construction, steel columns located on the corners of buildings were often encased in brick. Water that migrates through the brick accesses the steel, which then begins to oxidize (rust). The pressure exerted by the steel is referred to as oxidized jacking. The pressures can reach levels capable of pushing the masonry away from the building,causing vertical cracking of the brick. This phenomenon can also occur horizontally along floor lines, when oxidized jacking of steel spandrel beams pushes brick out of plane. In newer, cavity wall construction, vertical cracking at outside building corners may indicate a lack of installed expansion joints. As with vertical cracking at inside corners, the two intersecting walls will expand and contract at different rates, causing rotation of the brick and eventual cracking. Studies have found that, for walls without the installation of control joints, a minimal brick expansion of 2mm to 4mm caused vertical cracking at building corners .Vertical Cracking above Window Heads: Deflection caused by an undersized lintel can cause the masonry to deflect at the center of a window opening and develop a vertical crack. The cracks will likely be tapered with the crack wider at the lintel, but decreasing in width as the crack travels upward away from the window. Diagonal Cracking and Cracking in the Field of the Brick Wall: Uneven settlement of the building foundations can cause diagonal cracking (sometimes referred to as step cracks due to the crack following the path of mortar joints horizontally and vertically) at fenestration (windows and doors), and in the field of the brick wall.Cracking at concrete foundations: Concrete and brick masonry expand and contract at different rates. If separation provisions such as a bond break or flashing are not installed between the concrete and brick, cracks occurring in the concrete foundation may continue through the brick or cracks may occur at the juncture of the brick and concrete.
Efflorescence is the formation of a white crystalline substance on the face of brick.This is caused by an excessive amount of moisture within the wall leaching through and out of the masonry. As water passes through the mortar joints, salts are collected and transported to the face of the brick where it then crystallizes.Efflorescence may often occur in brick of newly constructed buildings.Efflorescence in this type of condition can often be easily removed by scrubbing the effected areas with water. However, efflorescence that occurs well after construction was completed generally indicates that a large amount of moisture has penetrated behind the brick and is unable to effectively drain back to the exterior. This results from many factors which may include weep drains becoming clogged or brick cavity walls being occluded with mortar droppings. Both of these conditions hinder or limit the ability for moisture to drain to the exterior.
Spalling is when portions of the brick flake off from the main body of the brick. Sometimes the spalled pieces can be very large portions of the original brick. There are several reasons that brick spalling may occur. Spalling may be caused by installation of brick coatings intended to not allow the brick to “breath” (moisture in the form of vapor not allowed to transmit through the brick to the exterior). When this occurs and is compounded by a lack of drainage provisions, moisture trapped behind the exterior surface of the brick will freeze and exert pressures in the brick material sufficient to break a portion away from the rest of the brick (spall). Spalling can also be due to the brick materials being made from soft clay material which will readily absorb moisture that may freeze within the brick, resulting in spalling. A third reason for spalling could be due to movement of the structure. The movement may exert sufficient pressures onto individual brick that breaks the brick apart. This latter phenomenon has its most common occurrence at structural lintels in buildings.
Visual evaluation of brick masonry walls for cracking patterns, efflorescence, and spalling can provide useful information regarding the structure and the installation of the brick wall. Seeing these types of issues can give the observer good insight into how the structure and the brick are performing. A visual evaluation will also determine if further testing is necessary.Cracking patterns indicative of building movement require determination of the cause to define if the building is still moving or is stationary. A simple way to determine if building movement is still occurring can be done by installing plaster over the crack.If the crack re-occurs through the plaster, building movement is still occurring and should be investigated for the cause of the movement. Another way to examine cracks is through use of electronic or manual crack meters. Crack meters will accurately measure the amount of change in crack width over a prolonged period of time. Invasive testing,involving removal of brick to uncover the underlying structure, may need to be performed to determine if the underlying structure is sound.