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Why is my stucco chimney cracking?
Saturday, November 20, 2021
There are several types of chimney structures that stucco is applied over, including brick and concrete block. But the stucco chimneys we see that have the most cracking problems are the wood-frame ones enclosing a manufactured metal fireplace flue. Stucco chimneys have the same problems as stucco over wood-frame walls: any water that gets behind the stucco through small cracks can become trapped if there is not a weep screed at the base. The trapped water corrodes the metal lath while spreading and enlarging the cracks, so the deterioration speeds up over time.
The problem can be controlled by regular repair of any small cracks as they appear. But, unlike the stucco walls below, early hairline cracks are not easy to see from the ground and stucco chimneys can be treacherous for a homeowner to access for minor repairs. So it often does not get addressed until the repair is major, and sometimes structural. At that point some homeowners decide to replace the stucco chimney facing with cementitious panels or another material.
Another reason stucco chimneys over wood-frame are especially vulnerable to cracking is because the wood structure expands and contracts primarily due to moisture changes, while the stucco responds to temperature changes. See our article Why is my stucco cracking? to learn more.
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