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INFORMATION BULLETIN REGARDING STUCCO CRACKING
Stucco is a colored cementitious material that is hard, brittle and water resistant. One might be fearful of cracks in stucco, but stucco has cracks like wood has knots. Cracking is inherent to the product.
The Stucco Manufactures Association recommends that stucco systems, be panelized every 150 to 200 square feet to control cracking. This is generally accomplished with expansion joints during initial construction. This type of panelization is normally accomplished on commercial buildings, but due to aesthetic considerations, rarely seen on residential homes. Adobe style homes with parapets will generally not have any type of expansion joints installed. Panelizing the stucco allows for the stucco to move as a single unit, within the panel, while minimizing cracking. When stucco is applied to larger areas, it will generally crack to relieve the stresses generated within the material from, thermal expansion and contraction, wind loading, moisture freeze / thaw cycles and movement of foundations from tree roots, seasonal heaving and receding and settling during the first few years after a structure is built. Cracks will typically appear at the corners of windows and doors and can extend diagonally for a couple of feet. Areas of dissimilar materials such as the transition of block walls to a wood framed structures will experience different rates of expansion and contraction and usually a crack will develop at this interface. When room additions are constructed against an existing structure, it is common that that the new and old structures are not completely married and therefore movement will take place and a crack may develop at that interface. Many times cracking will develop at the “sill plate” which is were the house wall systems sit on the concrete foundation. These cracks are easy to identify as they will appear approximately six to twelve inches above the grade and extend perfectly horizontal, sometimes for many feet.
When a structure has been restored with a new stucco color coat, the colored cement stucco material is approximately 3/16” thick. Some preexisting cracks may have been repaired prior to the color coat but other times the color coat may fill minor cracks and offer a better aesthetic solution. The new color coat is mostly aesthetic, not structural, and will help to bridge some of the cracks that have stabilized, but can typically re-crack due to movement in the wall by the above mentioned causes. Cracks can occur immediately after a stucco restoration has been accomplished. If the wall is not moving, the stucco will generally not crack. Cracking is not always a problem for the integrity of the stucco system. The general rule of thumb is that cracks on the vertical wall surface, less than a width of a nickel (1/8” thick), are considered hairline and do not pose any threat to the integrity of the stucco system. Cracks on the vertical walls that exceed 1/8” and extend into the base coats should be addressed with a good crack patching procedure. Cracks of any size on parapet caps should be sealed promptly to avoid moisture intrusion.
Even premium synthetic stucco systems such as Sto, Synergy and Parex to name a few are more resistant to cracking, but if applied over a cement base, cracking will most likely occur. This should not necessarily be construed to be a failure of the material or application. Synthetic stucco finishes are more elastic, and will tolerate more movement in the wall than cementitious stucco finishes, before they are breached, but still they are subject to the same physics as cement stucco finishes.
Considering cracking will at some point in time occur to all stucco and synthetic stucco systems applied over a cementitious base, manufactures or contractors do not warranty against cracking. A successful regiment of water management and periodic maintenance should give one many years of durability and satisfaction, for a well applied product. For a crack repair procedure, please see the accompanying bulletin on “Caulking of Stucco…Tech Bulletin” or feel free to call us at 505-345-3200, if you have any further questions.
Copyright 2011. Reule Sun Corporation.