Masonry walls sometimes show signs of bulging as they age. A wall itself may bulge, or the bulge may only be in the outer wythe. Bulging often takes place so slowly that the masonry doesn’t crack and, therefore, it may go unnoticed over a long period of time. The bulging of the whole wall is usually due to thermal or moisture expansion of the wall’s outer surface, or due to contraction of the inner wythe. This expansion is not completely reversible because, once the wall and its associated structural components are “pushed” out of place, they can rarely be completely “pulled” back to their original positions.
The effects of the cyclical expansion of the wall are cumulative and, after many years, the wall will show a detectable bulge. Inside the building, separation cracks will occur on the inside face of the wall at floors, walls and ceilings.
Bulging of only the outer masonry wythe is usually due to the same gradual process of thermal or moisture expansion; masonry debris accumulate behind the bulge and prevent the course from returning to its original position.
In very old buildings, small wall bulges may result from the decay and collapse of an internal wood lintel or wood-bonding course. This can cause the inner course to settle and the outer course to bulge outward.
When wall bulges occur in solid masonry walls, the walls may be insufficiently tied to the structure, or their mortar may have lost its bond strength. Large bulges must be tied back to the structure; the star-shaped anchors on the exterior of masonry walls of many older buildings are examples of such ties (check with local building ordinances on their use). Small bulges in the outer masonry course often can be pinned to the inner course or dismantled and rebuilt.
Although masonry can deform elastically over long periods of time to accommodate small amounts of movement, large movements normally cause cracking. This is known as masonry cracking.
Cracks may appear along the mortar joints or through the masonry units. Cracking can result from a variety of problems:
- differential settlement of foundations;
- drying shrinkage (particularly in concrete block);
- expansion and contraction due to ambient thermal and moisture variations;
- improper support over openings, the effects of freeze-thaw cycles;
- the corrosion of iron and steel wall reinforcement;
- differential movement between building materials;
- expansion of salts; and
- the bulging or leaning of walls.
Differential Settlement Caused by Variable Soil Types
Cracks should always be evaluated to determine their cause and whether corrective action is required. Look for signs of movement. A clean crack indicates recent movement; a dirty or previously filled crack may be inactive. A pocket lens may be useful for such an examination.
Correlate the width of larger cracks to the age of the building. A 1/2-inch crack in a new building may be a sign of rapid settlement, but in a building 50 years old, it may indicate a very slow movement of only 1/100 of an inch (0.25 mm) per year. In each case, the cause and treatment may differ.
Crack movement can be measured with a commercially available joint movement indicator. This device is temporarily fastened over the crack and a scribe records movement over a period of time. Cyclical movements may take six months or more to measure, but diurnal movements can be recorded over a few days. Hand measurements can also be made of crack movements, but these will be less precise and require repeated field visits. All tests should be performed by a licensed contractor.
Cracking Associated with Drying Shrinkage in Concrete Block Foundation Walls
The shrinkage of concrete block walls during the drying process will often result in patterns of cracking similar to that caused by differential settlement: tapering cracks that widen as they move, resulting in a diagonal upward pattern. These cracks usually form during the building’s first year and, in existing buildings, will appear as “old” cracks and exhibit no further movement. Although such cracks are often mistaken for settlement cracks, shrinkage cracks usually occur in the middle third of the wall, and the footer beneath them remains intact. Shrinkage cracking is rarely serious and, in an older building, may have been previously repaired. If the wall is unsound, its structural integrity can sometimes be restored by pressure-injecting concrete epoxy grout into the cracks, or by adding pilasters.
How back-filling can affect foundation walls:
How horizontal cracks relate to foundation wall movement:
Visually inspect your foundations at least annually. For concrete slabs, look for cracks, soil separation from the edges of the slab, water stains or discoloration, or evidence of pest intrusion (mud or mounds of dirt on the slab edges). In a climate with elastic soils, some cracking is not unusual. But large cracks (greater than ¼-inch) should be evaluated by an expert, especially if any buckling or warping of walls or floors is also present.