November 3, 2023
Crazing, a term that may be unfamiliar to many outside the construction industry, is a common phenomenon that can affect the surface of the concrete. If you've ever noticed a network of tiny cracks creating a pattern similar to a roadmap on a concrete surface, then you've seen something called crazing.
While it might appear unsettling, it's essential to understand what crazing truly is, the causes behind it, and its implications for the integrity of the concrete.
What is crazing in concrete: Crazing refers to the development of a network of fine random cracks or fissures on the surface of concrete caused by shrinkage of the surface layer. These surface cracks are rarely more than a few millimeters deep and are generally not structurally significant, meaning they don't typically threaten the stability or integrity of the concrete structure.
Crazing cracks (spider cracking) can be unsightly and may reduce the surface durability of the concrete. The primary concern with crazing is aesthetics. Over time, dirt fine sand can accumulate in these small cracks, making them more visible and potentially detracting from the appearance of the concrete surface.
Understanding the causes of crazing can help prevent it in future projects. There are several factors that can contribute to crazing:
Crazing cracks in concrete are generally the result of improper practices during the mixing, pouring, or curing of the concrete, as well as environmental conditions. While these cracks are usually only superficial, they can detract from the appearance of the concrete and may increase its susceptibility to wear and tear over time.
Here are some of the best ways to prevent concrete crazing:
Crazing in concrete is generally more of a cosmetic issue than a structural one, as the cracks are usually quite shallow and do not penetrate deep into the concrete. However, if the appearance of crazing on your concrete bothers you, there are ways to mitigate it:
Here's a step-by-step guide on how to repair concrete crazing by resurfacing the concrete using a thin concrete overlay material:
1. Clean the Surface: Begin by cleaning the surface thoroughly. You can use a power washer or a stiff broom along with a concrete cleaning solution to scrub off any dirt, oil, or other contaminants. The overlay material needs a clean surface to properly adhere.
2. Repair Major Cracks or Damage: If there are any larger cracks or damages present apart from the crazing, these should be addressed first using a concrete repair compound. Follow the manufacturer’s instructions to apply it.
3. Mix the Overlay Material: Following the manufacturer's instructions, mix the overlay material. Some products will only require adding water, while others may have more complex mixing procedures. Always follow the manufacturer's instructions for the best results.
4. Apply the Primer: Many overlay materials require the application of a primer before the overlay material is applied. The primer helps the overlay material bond to the existing concrete. Apply the primer as per the manufacturer's instructions.
5. Apply the Overlay Material: Once the primer is dry, you can apply the overlay material. Typically, this is done using a trowel or squeegee. The thickness of the application will depend on the specific product and the depth of the crazing, but generally, it's between 1/8 and 1/4 inch. Make sure to spread the material evenly over the surface.
6. Texture the Surface (Optional): If you desire a textured finish, you can add texture while the overlay material is still wet. This can be achieved using a variety of tools such as a broom, trowel, or texture roller, depending on the desired effect.
7. Allow the Overlay to Cure: After application, allow the overlay to cure according to the manufacturer's instructions. This time can vary, but it is often between 24 to 48 hours. The surface should be kept clear and free from traffic during this time.
8. Seal the Surface: Once the overlay has fully cured, apply a high-quality concrete sealer. This will help protect the new surface from stains, weathering, and wear, and will often enhance the color and appearance of the overlay.
Remember, repairing crazing with a concrete overlay is a cosmetic solution. If crazing is a recurring problem, consider reviewing the concrete mix design, placement methods, finishing techniques, and curing procedures to minimize the occurrence of crazing in future projects.
PRO TIP: You can't fix crazing by sprinkling cement on the surface and working it in. Never sprinkle cement on the concrete to try and fix it.
Crazing in concrete is not necessarily abnormal or uncommon, but it's not an ideal or desired characteristic either. These are superficial, very fine cracks that appear on the surface of the concrete, forming a pattern that often resembles a spiderweb or map. They don't affect the structural integrity of the concrete but can detract from its aesthetic appeal.
Crazing usually results from improper curing, overworking the surface during finishing, using a high water-cement ratio in the mix, or rapid drying due to environmental conditions. It's most commonly seen in concrete slabs or flatwork.
So while crazing may not be abnormal in the sense that it does occur under certain conditions, it's something that concrete professionals try to avoid to ensure the best appearance and longevity of the surface. Proper practices in mixing, pouring, finishing, and curing concrete can help prevent crazing.
Once formed, crazing cracks usually don't get deeper or wider over time under normal conditions.
However, the visibility of crazing can increase over time due to the accumulation of dirt and debris in the fine cracks. Furthermore, if the concrete surface is exposed to severe wear and tear or aggressive environmental conditions, these superficial cracks can potentially serve as initiation points for more serious deterioration.
For example, in colder climates, if water gets into these cracks and then freezes, it expands and could cause the cracks to enlarge. Similarly, exposure to certain chemicals or salts can also worsen the condition of crazed concrete over time.
So while the crazing itself might not get worse, external factors can lead to a worsening appearance or further surface damage over time. Regular cleaning and maintenance, like sealing, can help mitigate these effects and keep the concrete looking its best.
Crazing in concrete, while not aesthetically pleasing, is generally not considered structural damage. These are superficial, fine cracks that form a pattern on the surface of the same concrete slab, and they don't typically compromise the integrity or strength of the concrete structure.
While both cracking and crazing are types of fissures that can occur in concrete, there are important differences between the two.
So, the main differences between crazing and cracking lie in their depth, pattern, the potential impact on the whole concrete floor's performance, and their causes. Understanding these differences is crucial in diagnosing issues with a concrete floor installation and determining the appropriate solutions or preventative measures.
No, craze cracks and plastic shrinkage cracks are not the same things. While both are types of cracks that can occur in a concrete slab, they differ in their characteristics and causes.
Plastic Shrinkage Cracks:
So, while both craze cracking and plastic (drying) shrinkage cracks are related to shrinkage and drying of the concrete, they differ significantly in their severity, appearance, potential impact on the concrete, and their causes.
In conclusion, crazing in concrete is a common phenomenon that results in a network of fine, shallow cracks on the surface of the material. While primarily a cosmetic issue, it can detract from the aesthetic appeal of the concrete and, under specific conditions, may lead to further surface degradation.
Prevention strategies, including proper curing, avoiding overworking the surface, and appropriate water-cement ratios, can help avoid crazing. If crazing occurs, it can be addressed using methods such as cleaning, sealing, or resurfacing, depending on the severity.
Understanding what crazing is, why it occurs, and how to address it can help maintain the durability and appearance of your concrete structures.