Stucco cracks are usually caused by wrong mixing proportions, insufficient or excessive mixing, drying shrinkage due to the rapid evaporation of water from the stucco, seasonal changes, and seismic movement. But there are two more less-common causes of cracks in stucco: the normal settling of the home and differential settlement.

While the cracks that occur naturally over time as the home settles are generally not a cause for concern—though these cracks should also be addressed before they cause any further issues—the cracks that develop as a result of differential settlement can have serious implications for any home. Because specific stucco cracks can lead to structural damage, a homeowner should be able to identify, diagnose, and evaluate the types of cracks that could develop in stucco over time.

Types of Cracks in Stucco

When it comes to stucco, cracks are almost inevitable. Although stucco is a durable siding material, its cement-based composition makes it fairly rigid and brittle. As a result, it cannot accommodate structural movement or the expansion and contraction of different building materials. To gain a better understanding of how and why cracks in stucco occur, let’s take a look at the various types of stucco cracks and their underlying causes.

Hairline Cracks in Stucco

Hairline cracks are typically about 1/16 of an inch wide. While these cracks aren’t as serious as wider cracks, they could still provide a pathway for water and moisture to enter your walls. Hairline cracks in stucco develop due to several different reasons, including:

  • very hot, cold, dry, wet, or windy conditions, which occur during the curing and drying process of newly applied stucco;
  • specific building materials, such as green lumber, which may change shape as they dry;
  • expansion and contraction of fresh stucco as it settles after the application;
  • expansion and contraction joints, which move slightly during the normal settling process;
  • inadequate spaces between the sheets of sheathing materials (e.g. wood, plywood, OSB, or gypsum sheets) used underneath the stucco;
  • incorrectly installed fiberglass mesh tape, which doesn’t cover the seam where two pieces of foam trim meet;
  • normal settling, which is caused by your home’s weight that compresses the soil beneath the foundation gradually and uniformly; 
  • thermal movement, which occurs as a result of the different expansion and contraction rates of various building materials subjected to temperature fluctuations.

Spider Cracks in Stucco

These cracks are also thinner than 1/16 of an inch and look like spider webs, hence the name. Although spider cracking could be the result of normal settling, it typically occurs when:

  • the base coat isn’t allowed to cure properly or dries too quickly;
  • the material is mixed incorrectly or insufficiently;
  • too much water is added to the mix;
  • the stucco is applied in extremely hot or cold weather.

Pattern Cracking in Stucco

Multiple vertical and horizontal hairline cracks that show up as a grid pattern are typically caused by the lath, which isn’t nailed on properly. Because the lath is loose behind the stucco, it causes the stucco to crack as time goes by. However, it’s essential to know that pattern cracking could also be a sign of differential settlement.

Deep, Wide Cracks in Stucco

While most stucco cracks are thin and small, so they usually represent just a cosmetic issue, one or more large cracks could develop occasionally. Wider than 1/16 of an inch, any deep or wide cracks in stucco indicate possible problems with the foundations. These cracks are divided into two main categories:

  1. Vertical and/or horizontal cracks – Large vertical and/or horizontal cracks could develop between two vertical walls, between walls and ceilings, or at joints between wood framing and brick/concrete masonry. Deep vertical cracks in stucco could also appear around window and door frames.   
  2. Diagonal and/or stair-step cracks – Diagonal and stair-step cracks are typical indicators of structural issues, which may occur as a result of differential settlement and/or seismic changes in the foundation. In general, differential settlement is caused by unsupportive soils, which may become displaced—due to insufficient compacting and/or undercutting repeated expansion-contraction cycles, or extreme weather conditions, like flood events—and can no longer provide adequate support for your home. Regardless of how large a diagonal or stair-step crack is, it should be inspected and repaired by a professional soon after you observe it.

All Cracks Are Dangerous

Superficial or deep, small or large, cracks in stucco allow moisture and water to pass freely through your walls. This could lead to extensive water damage, rot, structural problems, and costly repairs down the road. As well, deep or wide stucco cracks are always an indicator of foundation damage. To prevent further damage and restore the structural integrity of your home, it’s important to address stucco cracks in a timely manner. If you’re unsure whether or not the cracks in your stucco indicate a small problem or foundation failure, have your home checked by an experienced foundation repair contractor. For a free consultation and repair estimate, contact our professionals today!

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