Correctly Repairing Stucco Cracks Key to Long Term Waterproofing Success


The exterior walls of an occupied building should, among other things, prevent excessive air and water from entering to the interior. In Florida, stucco is a common choice for exterior wall cladding, but after time, cracking can become a problem. Although control joints are typically used during construction to minimize stucco cracking and to accommodate building or thermal movement, and although construction standards apply to the use of these joints, cracks can still occur.

In most cases, stucco cracking is simply a normal part of the aging of a building during the first few years after construction since the building will experience settling and movement that commonly appears as cracks in the stucco. However, stucco cracks can compromise the weather resistance of the exterior wall, and under the right conditions are potential moisture intrusion points. Factors such as crack/void size, location, wind direction and wind speed will determine where and how rapidly the water enters into or through the stucco.

Stucco cracks should be repaired, but too often we see that an elastomeric coating is recommended because it provides the “advantage” of a crack bridging ability. While these coatings can accommodate the thermal movement, withstand wind driven rain, and provide a long term warranty, they do not bridge or repair existing cracks. The crack bridging ability applies to new cracks that may occur after the stucco has been coated.

When exterior building maintenance is undertaken after the first few years of building life, or anytime thereafter, cracks need to be repaired as part of preparation for a the new paint coating. This is a standard coating manufacturer’s requirement, and these repairs are normally included as part of the manufacturer’s warranty. By correctly identifying the cracks and implementing the proper repair before re-coating walls, it is possible to provide successful long term performance.

Stucco cracks generally include two types. These are static or dynamic (moving) cracks. Static cracks are often hairline in size and less than 1/16th inch in width, and these tend to have a crazed or spider web pattern. The reasons for this type of cracking vary, but the cracks are considered non-moving.

Static Cracks Example 1Static Cracks Example 2: Dynamic cracks are normally larger and occur because of ongoing movement occurring at the crack location. The most common locations for dynamic cracks are cold joints between different substrates such as the joints between poured concrete and wall framing or CMU blocks. Other common locations include intersections of vertical walls and the corners of wall openings such as for windows and doors.

Repairing stucco cracks prior to re-coating a building requires a thorough inspection, and since different types of repairs are required for different types of cracks, the inspector needs to identify the cracks accordingly. To assure finding all the cracking, the inspections should be done in the cool of the day when the crack is at its largest. If the finish of the stucco creates a contrast, evenly fog the surface with moisture and as the surface dries, the cracks are more easily identified. The cracks should be traced with Magic Marker pens for identification and different colored pens can be used to identify the type of repair that will be necessary.

The repair of smaller and static cracks generally uses a brush-grade acrylic elastomeric patching compound over the crack which is feathered out at the edges. At larger static cracks, the crack is raked out to form a “V” shaped groove and a knife-grade acrylic elastomeric patching compound is then installed in the groove and feathered at the edges. For dynamic cracks and other cracks larger than 1/16” wide, the crack location is to be ground or saw cut to create a joint that is filled with polyurethane sealant.

Crack repair work should be completed by a qualified and experienced remedial Waterproofing Contractor. Their personnel are familiar with the crack repairs, stucco preparation and the coating systems.

Before starting the work, a sample area representing the full scope of crack repairs should be selected as a mock-up. The mock-up can be completed for acceptance and approval of by all parties before proceeding with the work. In this way, adjustments to the repair process and scope can be made before the work begins, and the mock-up serves as a basis of acceptable work for the balance of the building.

Completing crack repairs in the exterior stucco is part of the preparation for a warranted, exterior coating application. However, it should be noted that additional cracking may occur during the course of the warranty, and as a result, future leaking could occur. Therefore, maintenance inspections and crack repairs should be done regularly.

Peter R. Craig specializes in the exterior waterproofing of exterior walls, decks, and below grade areas. Born and educated in Cape Town, South Africa, he has been with Glazing Consultants since 1997. He has over 25 years experience in the waterproofing industry in both new construction and restoration waterproofing. He combines his extensive knowledge of products, techniques and his practical experience to provide answers, solutions, guidance and long term maintenance programs. His expertise includes stucco, EIFS, vertical wall coatings, expansion joints, concrete repair materials, deck membranes and sealers, and sealants.

Mr. Craig is a member of ASTM and CSI and a certified third party inspector for CETCO Waterproofing products. He has also been the featured speaker at numerous Building Managers and Condominium Association meetings and has published articles in the past for Condominium Management Magazine.