Cracks in masonry can scar a building's architectural appearance. Or they can be the first telltale signs of a potential wall collapse. Thus no crack should go unexamined. For every crack, a trained investigator should record, with photographs and sketches, the following information: location, pattern, length, width, depth, age, and if the crack is moving or dormant. Based on this information, an investigator can assess the cause of the crack, how harmful it is, and how best to repair it. MEASURING CRACK WIDTH To measure the width of cracks, most investigators use a crack comparator although a graduated magnifying device is more accurate. WHEN IS A CRACK TOO WIDE? Whether a crack is too wide depends on the material, the type of building, the climate, and the type of crack. BEWARE THE MOVING CRACK The difference between an active or working crack and a dormant crack is important. An active crack may open or close, but a dormant crack has stopped moving. If the crack is dormant, then it can be filled with a rigid filler, such as epoxy or cement. Working cracks, on the other hand, should be filled with flexible sealants. How do you tell if a crack is active or dormant? There are three ways. The easiest is to measure the crack width at regular time intervals. Another method is to spot patch the crack with plaster. Note the date the patch was placed and inspect it at regular intervals to see if it has cracked. A two-piece crack monitor that sells for less than $15 also can be used to detect crack movement.