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    The inherent problem with stucco on a wood frame structure is that wood moves around—expanding, shrinking, and sometimes twisting—with changes in humidity. Wood is also somewhat flexible. Stucco, on the other hand, is comparatively stable and stiff, but it expands and contracts with changes in temperature more than wood. When you apply a stucco surface to a wood wall, there must be built-in details to keep the differing movement of the two materials from cracking the less-flexible stucco. 

    The Florida Building Code uses the ASTM C-926-06 specifications for the application of stucco, which refers to it by the more technically correct name of “Portland Cement-Based Plaster.” The specs are based on these five time-tested standards:

  1. 1)THICKNESS - Stucco should be at applied in three coats, at least 7/8” thick (not including any texture) to resist cracking.

  2. 2)FLEXIBLE EXPANSION JOINTS - Placed at regular intervals along the wall, they absorb the expansion and contraction of the stucco due to temperature changes. These are also called control joints.

  3. 3)WEEP SCREED - A weep opening at the bottom of the wall lets any water that penetrates the stucco drain out behind it, instead of getting trapped and rotting the wall framing. When a wood-frame second floor is built on a concrete block first-floor structure, the weep screed will be a strip located at the bottom of the second floor level.

  4. 4)CASING BEADS - These wrap around anything that penetrates the stucco surface—such as windows, doors, and soffit returns—to provide a gap that can be caulked and prevents hairline cracks that will admit water into the wall.

  5. 5)DRIPS - At any change of plane from a vertical to a horizontal under-surface of the stucco, a drip edge lets water fall off at the corner and not migrate sideways due to surface tension.

    All of this differs dramatically in complexity from the installation of regular siding, which depends on simple down-lapping of smaller pieces of building material for waterproofing, and movement is absorbed by the numerous overlapping joints, plus caulk around doors and windows.

     If any of the five anti-cracking measures are ignored, you will have a stucco problem. Maybe not immediately, because it takes a few years for the initial small cracks to let in some water, which rusts the steel lath, and opens the cracks further, letting in even more water...and so forth. But it will happen.

     Here’s a listing of how each one of the five can be done wrong:

  1. 1)THICKNESS - When the total of the three coats of stucco dips below 7/8-inch thick, those areas are more prone to cracking. Sometimes only two coats are applied, with not enough curing time between coats. Also, if the backing paper and lath is sloppily installed, it can create pockets of thin coverage.

  2. 2)FLEXIBLE EXPANSION JOINTS - The total area of stucco between expansion joints should not exceed 144 square feet, with the additional restrictions that the joints not be more than 18 feet apart along the wall and a length-to-height ratio that does not exceed 2.5 to 1. The expansion joints should be tied to the metal lath only, not attached to the wall sheathing underneath, so that the joints can move independently from the wall structure. Metal lath that is continuous behind the expansion, connecting both panels, defeats the joint. Expansion joints that are placed too far apart or attached directly to the wall sheathing will also not do their job. A crack along the side of an expansion is an indication that it was likely not installed properly.

  3. 3)WEEP SCREED - No matter how carefully stucco is installed, some small cracks will appear over time. Trapped water wets the wood structure and starts rot when there is no opening at the bottom of the wall or the opening is obstructed. Some weep screeds have protective tape over the drain holes that should be removed after installation and gets forgotten.

  4. 4)CASING BEADS - Sometimes they are simply not installed. Without a groove to apply flexible caulk, cracked stucco along the side of a window frame is a common place for the stream of rainwater that runs down the side of a window to enter the wall.

    It begins as in the photo above, but buckling stucco and staining follow over time. The photo below shows typical damage in the wall framing from this defect.

  5. 5)DRIPS - They are not as aesthetically pleasing as a simple corner bead where vertical surfaces return back horizontally, but ugly water intrusion damage ensues if a 1/4” minimum drip edge is not installed. The photo below shows the rotted wood sheathing found under the stucco at the corner of an open porch with this defect.

     Other defects that can cause stucco cracking include: not enough fasteners securing the metal lath, undersize fasteners that do not penetrate deep enough into the wall sheathing, improper lapping of the building wrap to the weep screed, and not leaving the required 1/8” gap between sheathing panels. Because many of the defects that allow water entry are concealed by the stucco itself, they cannot be verified without digging into the wall. But their symptoms bloom and spread on the wall surface over time.

    It usually takes five to seven years or more from time of construction to see clear signs of distress in stucco walls that are the result of defective stucco installation. But every stucco finish will develop a few hairline cracks, so we recommend checking for them at least once a year, and sealing the cracks with a masonry caulk. 

    Repainting the walls and touching up the caulking every 7 to 10 years is also a good idea, since paint and caulk are your first layer of protection from water intrusion. Because home builders occasionally claim that inadequate maintenance of the wall finish is a contributing factor in stucco failure claims from their customers, your diligent maintenance may have the added benefit of helping you secure your claim for damage to your home if it is due to defective stucco installation. 

    When the cracks multiply and get worse, in spite of your maintenance and repairs, we suggest calling a professional inspector for further evaluation. The one you choose should be familiar with the installation standards and have some experience in diagnosing stucco problems, plus carry a couple of moisture sensing tools, such as an infrared camera and an electronic moisture meter, in their tool bag.

    If you are wondering why older homes with stucco walls don’t have the same severe cracking problems as outlined above, it is because most of them are stucco over concrete block. The block has a similar rate of expansion and contraction as stucco, and concrete block is more forgiving of a little moisture intrusion. It can absorb and dissipate through evaporation any small amounts of water that penetrate the stucco.

    The thickness of stucco, along with sufficient curing time between coats, also makes a stronger surface, and older homes that are of similar stucco-over-metal-lath are more likely to have been done correctly.

While we hope you find this series of articles about home inspection helpful, they should not be considered an alternative to an actual home inspection by a local inspector. Also, construction standards vary in different parts of the country and it is possible that important issues related to your area may not be covered here.
© McGarry and Madsen Inspection


More Blog Posts on Similar Subjects:

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  2. What is the difference between Acrocrete and EIFS?

  3. Do stucco walls mean a house is concrete block?

  4. What should I bring to the home inspection?

  5. Can vinyl siding be painted?

  6. Should I be suspicious about a concrete block house covered with siding?

  7. How do I remove cigarette odor in a house?

  8. Do you have any home inspection tips for buyers?

  9. There’s an old fuel oil tank underground in the yard. Is it a problem?

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  12. Should I buy a fixer-upper?

  13. What happens at a home inspection?

  14. What’s my chance of buying a Gainesville home over a sinkhole?

  15. I’d swear that crack wasn’t there yesterday. What happened?

  16. Is my house near that Superfund cleanup site in Gainesville?

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  18. What can you tell me about buying a house with structural problems? It’s priced cheap!

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  23. How do sellers try to fool the home inspector?

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  26. What is the difference between an FHA inspection and a home inspection?

  27. What are the common problems of different types of house foundations?

  28. What is the average life expectancy of a house?

  29. What is the life expectancy of stucco?

  30. What is the average life expectancy of plywood siding?

  31. Why is a double cylinder deadbolt lock on an exterior door a safety hazard?

  32. What is Z-flashing?

  33. What is the difference between a clip, single wrap, and double wrap for the wind mitigation form?

  34. What is a “continuous load path”?

  35. Is a ridge board/beam required for a roof framed with rafters?

  36. What are the pros and cons of aluminum siding?

  37. Why does the laminate wood floor move when I walk across it?

  38. What causes paint to peel prematurely on the exterior of a house?

  39. What does freeze damaged brick look like?

  40. What are the common causes of ceiling stains in a house?

  41. What are the pros and cons of concrete block versus wood frame construction?

  42. What causes the surface of old bricks to erode away into sandy powder?

  43. Why is a horizontal board running along the bottom of the plywood siding of the house?

  44. Why would a house with Hardieplank siding have exterior wood rot problems?

Photo - Mark Cramer
Photo - Mark Cramer
Photo - Mark Cramer
Photo - Mark Cramer

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