Accordingly, cleaning of the masonry may be required prior to applying tuckpointing efforts. It should be noted that because of dirt deposits and stains, matching existing mortar color of old buildings may be difficult. Variations in the age of the mortar when the tooling is performed as well as the tooling pressure are suggested as well since both affect color and texture. If the identity of the original mortar materials is unknown, trial batches of different mix designs should be applied in test joints, tooled, and aged for a period of at least one week. Unless the wall is to be parged or coated, efforts should be made to match the color and texture of the new joints to the old. If the cracking is not extensive, confined primarily to the mortar joints, and relatively stable in width, it can be readily repaired by conventional tuckpointing (also called repointing) methods as detailed in Figure 1. Before retrofitting any building with control joints, consult a qualified design professional. The sealant will prevent water, dirt, or insects from entering the structure. Finally, the newly cut joint should be cleaned, filled with a backer rod and caulked as recommended by the manufacturer. The joint should extend completely through the wall and be approximately ⅜-inch (10 mm) wide, or one mortar joint wide. Next, a vertical joint is saw-cut at the location of a head joint through the mortar and masonry units. Installation of control joints in an existing structure is completed by first determining the location and spacing of required control joints by an approved method. If it is determined that cracking is present due to the lack of, or inadequate spacing of control joints, it may be necessary to retrofit the structure with control joints. The benefit associated with implementing crack width and/or deflection measuring gauges is that qualitative data is obtained which can be used to determine an appropriate crack repair method. Additionally, a variety of gauges can also be used to routinely monitor crack widths. A simple but fairly effective method of determining if a hairline crack is continuing to propagate or widen is to patch over a small length of the crack with gypsum plaster and monitor the patch regularly for several days. Since the necessary corrective action required in crack repair is highly dependent on the cause of the crack and whether the crack is stable (the crack has stopped getting wider), significant attention should be focused on these issues. Due to the highly complicated and problematic nature of such cracks, the reader is encouraged to seek the aid of a qualified design professional for recommendation on corrective actions for differential settlement.Īny objectionable crack should be analyzed to determine the cause and any previous corrective measures taken to prevent or accommodate the movement before additional repairs are made. The next leading cause of cracking in concrete masonry walls is differential settlement due to uneven support of the foundation. Shrinkage cracking and crack control strategies are covered in more detail in TEK 10-1A, TEK 10-2C, and TEK 10-3 (ref. Although the net resulting shrinkage in a finished structure can vary considerably (for example, temperature movements can vary greatly with exposure and unit color, while drying shrinkage can be expected to be higher for units having a higher cement content), the combined effect of these shrinkage components could be sufficient to cause large tensile cracks in the masonry if proper precautions are not taken. Once placed in a structure, concrete masonry units are subject to a variety of forces and stresses which, besides structural loads, include shrinkage stresses due to drying, temperature fluctuations, and carbonation (an irreversible reaction with carbon dioxide in the atmosphere).
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