By Bud Coburn
Different environments have different effects on building materials. Specific climate conditions have their own special concerns and problems. For example, damage from freeze-thaw cycles can be a major issue in a cold-weather climate such as upstate New York that will not be relevant for the arid climate of western Arizona.
Bodies of salt water near the building or climates of extreme humidity may contribute to increased efflorescence.
Acid rain caused by industrial pollution may be the culprit in damage to limestone, sandstone and marble structures.
Vibrations from major nearby roadways or railways can sometimes cause damage to mortar joints.
Nearby excavations for subways or deep foundations for skyscrapers can sometimes lower water tables and cause soil problems that eventually lead to foundation issues.
Terrain and Vegetation
It may be useful to determine the type of soil around the building, since different types of soil drain moisture in different ways. Poor soil drainage may eventually lead to structural damage.
Proper surface drainage around the house is important. The grade should slope downward and away from the structure.
Ivy and other species that grow on exterior walls can sometimes penetrate and damage mortar joints, and their leaves may make it difficult for porous masonry materials to dry completely after rainfall.
Here are some examples of different forms of cracking that inspectors may encounter, as well as how to identify each type.
- Shrinkage or expansion, especially in concrete block, causes cracking, usually appearing in the building’s first year. During curing, expansion and contraction occur. Water evaporates as concrete block cures, causing the concrete to shrink. Clay brick absorbs moisture as it cures, causing expansion. Joints are built into walls in order to accommodate this movement, and cracking can be the result of improper joints. These cracks are rarely serious and can be identified as tapering cracks that widen as they move upward diagonally. Shrinkage cracks are often mistaken for settlement cracks, but they will usually appear on the middle third of a wall, with the footer beneath them remaining intact. Pressure-injecting concrete epoxy grout or adding pilasters can sometimes help restore structural integrity in a case where a wall is found to be unsound.
- Sweeping or horizontal cracking can be the result of several factors, including improper back-filling, vibrations from heavy machinery or vehicles in close vicinity to the wall, or freezing, swelling and heaving of water-saturated soil next to the wall. This type of cracking is potentially serious because it indicates that the foundation wall, which is the vertical supporting member carrying a portion of the structure above, is basically bent or broken. Complicated repairs may be necessary in this case, possibly including jacking and reinforcing the wall with interior buttresses, lowering the ground level around the building to relieve lateral pressure, or pressure-injecting concrete epoxy grout into the wall.
- Uneven settlement can cause cracking and structural problems, though it is relatively uncommon, and moisture and thermal movements are often incorrectly diagnosed as settlement problems. Settlement will usually occur early in the life of a building or if there is a drastic change in underground conditions, and is often associated with improper foundation design. Some signs of settlement include vertical distortion or cracking of masonry walls, warped interior/exterior openings, sloped floors, and sticking doors and windows. Cracks from uneven settlement are most likely to be found at corners and adjacent openings, and usually follow a rough diagonal along mortar joints, and may extend through contiguous building elements, such as floor slabs and interior plaster work. While major settlement cracking can be an issue, minor cracks are only structurally harmful if they allow moisture to penetrate.
- Cracking in masonry piers may occur if piers have rotated or settled differentially, or are subject to frost heaving or are damaged by freeze-thaw cycles. While the cracking may not be serious, structural wood-bearing components can lose bearing if piers move or deteriorate.
- Other causes of cracking can include walls leaning or bulging, salt crystals expanding inside the pores of the masonry, iron or steel wall reinforcements corroding, poor practices during construction, and inadequate support over openings. Also, minor cracking that resembles spider veins occurs naturally during the curing process of cement. These cracks are normal and no cause for alarm, unless they grow, which would indicate a potential problem requiring further investigation.
Excess moisture in masonry may be indicated by a white, staining deposit called efflorescence. This white staining is actually a salt deposit left by water that contained dissolved salts that evaporate after penetrating a masonry structure. Salts can also be present in all kinds of masonry materials, including brick, mortar, concrete block, plaster and stucco.
Efflorescence can be unsightly, and may also be an indicator that excess moisture may be present in the masonry, which can lead to problems. Salt crystals deposited inside the pores of the masonry can sometimes lead to cracking when they expand. Any observed efflorescence should be cleaned off of surfaces.
Steel Lintel Deflection
Lintels are beams that span openings in masonry walls, such as windows and doors. Reinforced masonry, pre-cast concrete and steel angles are all commonly used as lintels, but steel lintels in particular can sometimes cause problems if they are deflecting too much. This is not a structural problem, but too much deflection can often crack the stiff masonry or cause the lintel to rest on a window or door frame and transfer the wall’s load to it, which will lead to problems down the road.
Moisture penetration puts routed cells, collar joints and steel rebar in bond beams at risk for corrosion. Anchors attaching veneer to a support, horizontal joint reinforcement, and ties that hold multi-wythe masonry walls together can each also be susceptible to corrosion. Once corrosion begins, rust is produced, which occupies up to six times the original volume of the steel. The expansion of volume leads to cracking of masonry, and this allows for even more water penetration, perpetuating the cycle.
While corrosion-resistant coating is beneficial for the reinforcing materials, and the alkaline nature of mortar helps prevent corrosion, tight mortar joints and proper flashing are essential for ensuring that water penetration does not lead to problems.
Flashing is extremely important for controlling and diverting the flow of water away from the masonry, and it is very common to see missing or improperly installed flashing. This will often lead over time to problems from moisture penetration, sometimes requiring costly repair.
Proper flashing should always be in place at the base, sill, head and roof locations, as necessary. The flashing should have end dams, and seams should be overlapped and sealed. Slip joints are necessary in metal flashing to allow for expansion and contraction with changes in temperature.
Flashing inside a masonry wall forms a gutter to collect any moisture that has penetrated the wall to divert it outside. This flashing is placed completely throughout a horizontal wall in mortar joints, with weep holes that allow the moisture to escape.
Mortar Deterioration and Poor Grouting Practices
Another problem arises when building codes and contractors do not distinguish between grout and mortar, which leads to the same mortar used for laying units being used to also fill cores. Only one type of mortar, Type M (per ASTM C270), actually meets the same strength requirements as grout, which has a 28-day compressive strength of at least 2,000 psi. This substitution of materials is not advisable.