An effective method for repairing or strengthening masonry walls, grout injection involves low-pressure injection of fine cement-based grout into cracks, voids, collar joints, or cavities. Grout injection has several applications: to repair and halt the spread of cracks; to increase a building's resistance to moisture penetration; and to strengthen retrofitted buildings, particularly historic structures and those in seismic areas. Grout is injected through holes drilled to intercept cracks and internal cavities. Use the smallest-diameter holes possible, drilled into mortar joints, to prevent chipping and damaging masonry units. To prevent damaging while strengthening already fragile masonry units, use a grout pump capable of limiting the pressure to about 8 to 10 psi. For collar joint injection, begin grouting holes at the base of the wall and proceed to the top, moving across the wall horizontally and then upward. Use low lift heights--about 2 feet or less--to prevent wall blowouts. Make sure the project engineer analyzes each situation.