General masonry inspection
Editor's note: This story is adapted from the U.S. Department of Housing and Urban Development's Residential Rehabilitation Inspection Guide, 2000.Click here for other stories in this series.
Parts of this story: Introduction ~~ Seismic and wind resistance ~~ Cracking and deterioration of masonry, general issues ~~Masonry foundations & piers~~Above ground masonry walls ~~Chimneys ~~Wood structural components ~~Iron and steel structural components ~~Concrete structural components
All exposed masonry should be inspected for cracking, spalling, bowing (bulges vertically), sweeping (bulges horizontally), leaning, and mortar deterioration. Before beginning a detailed masonry inspection, determine which walls are load-bearing and which are not. Usually this can be done by examining the beams and joists in the buildings basement or crawl space or attic. Note also whether the walls are solid masonry or masonry cavity, or whether they are non-structural brick or stone veneer. The overall quality of the buildings construction, and often that of its neighborhood, will be a good indicator of the condition of its masonry.
|A common masonry wall crack probably caused by thermal or moisture expansion. If possible, monitor such cracks over a period of time to see if theyre active. Active cracks should be sealed with a flexible sealant; inactive cracks may be pointed.|
There may be a substantial difference in the masonry walls in buildings built during the last 40 to 50 years compared to those constructed earlier. Walls became thinner as designers began to exploit more effectively the compressive strength of masonry by using higher strength masonry materials and mortars. This change came at the expense of flexibility as such walls are often more brittle than their massive ancestors and, therefore, more subject to stress-induced damage.
Two methods of testing are sometimes useful for assessing masonry.
See a qualified masonry consultant for the proper use of these tests on existing masonry.
Although masonry can deform elastically over long periods of time to accommodate small amounts of movement, large movements normally cause 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 sup-port 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.
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 one-half-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.
Cracks associated with thermal expansion and contraction may open and close with the season. These are cyclical cracks, which may gradually expand as accumulating mortar debris jams them farther apart after each cycle. Such cracks should be cleaned and protected by flexible sealants; re-mortaring cyclical cracks will hold them open and cause more cracking.
When there are masonry problems, it is advisable to procure the services of a structural engineer. If problems appear to be due to differential settlement, a soils engineer also may be required.
The two important qualities of mortar are its ability to bond to masonry and its internal strength. A sign of poorly made mortar may be random cracking at the bond joint. Until about the end of the 19th century, the standard mortar for masonry was a mixture of sand and pure lime or lime-possolan-sand. These low-strength mortars gave masonry the ability to absorb considerable strain. Accordingly, the tendency to crack was reduced and when cracks did appear in the mortar joints, they were to a great extent capable of chemical reconstitution or self healing. Thus, the age of the building may be a good clue in evaluating its mortar problems. Older mortar (or mortar of any age that uses hydrated lime) will be softer and may require pointing, but otherwise may be responsible for a sound wall.
Most often, mortar deterioration is found in areas of excessive moisture, such as near leaking downspouts, below windows, and at tops of walls. In such cases the remedy is to redirect the water flow and point the joints. Pointing should be performed with mortar of a composition similar to or compatible with the original mortar. The use of high-strength mortar to point mortar of a lower strength can do serious damage to the masonry since the pointing cant flex with or act in a similar way to the rest of the joint. It is useful to remember that mortar acts as a drainage system to equalize hydrostatic pressure within the masonry. Nothing should be done to reduce its porosity and thereby block water flow to the exterior surface.
To determine the composition (percentage of lime and other materials) of existing mortar, remove a sample and have it chemically analyzed by a testing laboratory. This should be done under the supervision of a qualified structural engineer.
Deterioration of brick masonry units
The spalling, dusting, or flaking of brick masonry units may be due to either mechanical or chemical damage. Mechanical damage is caused by moisture entering the brick and freezing, resulting in spalling of the bricks outer layers. Spalling may continue or may stop of its own accord after the outer layers that trapped the interior moisture have broken off.
Chemical damage is due to the leaching of chemicals from the ground into the brick, resulting in internal deterioration. External signs of such deterioration are a dusting or flaking of the brick. Very little can be done to correct existing mechanical and chemical damage except to replace the brick. Mechanical deterioration can be slowed or stopped by directing water away from the masonry surface and by pointing mortar joints to slow water entry into the wall. Surface sealants (damp proofing coatings) are rarely effective and may hasten deterioration by trapping moisture or soluble salts that inevitably penetrate the wall and in turn cause further spalling. Chemical deterioration can be slowed or stopped by adding a damp proof course (or injecting a damp proofing material) into the brick wall just above the ground line. Consult a masonry specialist for this type of repair.