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McGarry and Madsen's home inspection blog for buyers of
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Does stucco need expansion joints?
Tuesday, December 10, 2019
Stucco does not require expansion/contraction joints (also called control joints) when directly applied to concrete, concrete block, or other masonry, except where there is a change from one material to another.
Stucco on wood frame construction is another story, because stucco has a different rate of expansion/contraction than the underlying wood framing. Wood is more responsive to changes in moisture, while stucco expands and contracts primarily based on temperature. So the two layers have conflicting patterns of movement and flexible joints are necessary. Here are the standards, based on ASTM Standard C1063:
•• Maximum18 feet length of any stucco panel.
•• Maximum 144 square feet area per stucco panel, reduced to 100 square feet for horizontal, curved, or angular areas.
•• Length-to-width ratio of stucco panel cannot exceed 2.5 to 1.
The home shown at the top of the page has a concrete block first floor and wood frame second, but lacks necessary expansion joints at second floor level. The photo was taken when the home was new, but many of these homes with inadequately installed stucco end up like the photo below after 7 to 10 years. Go to our blog post Why is my stucco cracking? for more details.
And here’s a closeup of an expansion joint, with a hairline crack stopped by the joint.
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To learn more about exterior walls and structures, see these other blog posts:
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