Once the area that is in need of repair has been identified, a number of repair options may be considered. For instance, small hairline stucco cracks usually are not serious and can be sealed with a thin coat consisting of the finish coat ingredients, or even with a coat of paint or whitewash. Larger cracks will have to be cut out in preparation for more extensive repair.

In fact, analyses of the existing stucco will help to pick a stucco mix compatible with the historic stucco. Generally, cement stucco will not be physically compatible with the softer and more flexible lime-rich historic stuccoes. The differences in expansion and contraction rates between lime stucco and cement stucco normally lead to stucco cracks. Selecting the appropriate stucco mix that is durable and compatible with the historic stucco on the building can involve considerable trial and error, and might require a number of test samples, and even more if it’s necessary to match the color. Compare the color, texture and composition of the samples with the stucco remaining on the building. Besides, the number and thickness of stucco coats used in the repair should also match the original.

Historic stucco repair generally follows most of the same principles used in plaster repair. To obtain a neat stucco repair, the area to be patched should be squared-off using a cold chisel and all deteriorated, severely cracked and loose stucco should be removed. A clean surface is necessary to obtain a good bond between the stucco and substrate thus the areas to be patched should be cleaned of all debris and plant growth, dirt, loose paint, oil or grease.

If the area to be patched is properly cleaned and prepared, a bonding agent is usually not necessary. However, a bonding agent may be useful when repairing hairline stucco cracks, or when dealing with substrates that do not offer a good bonding surface. A good mechanical bond is always preferable to reliance on bonding agents. However, bonding agents should not be used on a wall that is likely to remain damp or where large amounts of salts are present as many bonding agents simply do not survive well under such conditions, and their use could jeopardize the longevity of the stucco repair.

When trying to save or preserve as much of the historic stucco mix as possible, give preference to patching rather than wholesale replacement. When repairing heavily textured surfaces, it is not usually necessary to replace an entire wall section. Because the textured finish, if well-executed, tends to conceal stucco patches, and helps them to blend in successfully with the existing stucco. However, patching a number of small areas scattered all over one location is not a wise repair approach unless the stucco has been previously painted, or is planned to be painted following the repair work. On unpainted walls such stucco patches are hard to conceal, because they may not match exactly or blend in with the rest of the historic stucco surface. For this reason it is recommended to carry out stucco repair works in a contained or well-defined area. In some cases, especially in highly visible locations, it’s better to re-stucco an entire wall section thus any differences between the patched area and the historic surface will not be so readily apparent.