Search Products

#1 Source for Professional Spray Foam Equipment

Premium Spray Foam Equipment

Spray Foam Rigs

The Most Common Concrete Slab Defects

The Most Common Concrete Slab Defects

Most people don’t think too much about the concrete slab beneath their buildings. Unfortunately, an “out of sight, out of mind” policy won’t work with your building’s foundation. The concrete slab provides stability and integrity to a building. If something goes wrong in the concrete, the entire property can suffer. That’s why concrete specialists must understand the most common concrete slab defects. When you know how to identify these problems and avoid them, you can deliver quality work to your clients every time. Stay informed and prepared with this guide to the problems you might come across while pouring, maintaining, or repairing concrete slabs.


Blisters are air bubbles that get trapped beneath the sealed surface of the concrete. These lead to small bumps and other imperfections on the surface. Generally speaking, blisters are a symptom of improperly mixed concrete. If you notice blisters during construction, alter your mix to eliminate the imperfections. That said, blisters don’t create any structural problems with the concrete slab. In fact, many buildings cover the blisters so that they’re unnoticeable once construction is complete. However, blisters can be an unsightly nuisance on exposed concrete floors. Stay vigilant while pouring so that you can catch blisters before you finish laying the slab.


Like blisters, delamination occurs when air bubbles or water get trapped beneath the sealed concrete surface. After laying a slab, you must give the concrete a chance to breathe. This allows air and water to escape before you seal the surface. Without this waiting period, air and water get stuck and lead to delaminated areas. These delaminated pieces can separate from the rest of the concrete and leave holes in the surface, creating an uneven foundation. Delamination is more common when the bleeding time is longer or when the surface setting time is faster. Factors like temperature or the specific concrete mixture affect both of these processes. The best way to avoid delamination is to give your concrete slab plenty of time to bleed before you seal it.


Cracking is one of the most common concrete slab defects. It’s also among the most annoying and problematic issues. Your concrete slab could crack for several reasons, including thermal contraction, subgrade settlement, applied loads, or drying shrinkage. The cause of the crack influences how severe it is. For example, shrinkage cracks don’t usually affect the structural strength of the building. Settling cracks, on the other hand, can wreak a lot of havoc on the building over time.

While you can take measures to prevent cracks from occurring while the concrete hardens, cracks that develop over time can prove particularly dangerous. These can create uneven foundations and harm the construction of the building. They also allow moisture to seep into the foundation. Fortunately, you can often repair cracks by resealing the flaw or lifting and leveling the slab.


Concrete curling occurs when the moisture or temperature at the top and bottom of the slab differ too much. For example, if the top of the slab dries off quickly in cool air, but the bottom of the slab sits against warmer, wetter ground, the edges of the concrete will rise and curl. For the most part, curling occurs during the drying process. This means you should catch and correct it before it becomes a major issue. However, if you don’t correct curling before building construction begins, the foundation will be uneven and lack stability.

Surface Scaling

Scaling is a form of concrete degradation. Thin layers of the concrete slab will peel and come off. As the surface layer falls apart, the overall strength and integrity of the slab decreases. This can cause more problems to develop with the slab as time goes on. Scaling is common in slabs with poor surface strength, which can occur due to a weaker mix or blisters and delamination. Alternatively, frequent freezing and thawing can cause the surface of the slab to weaken. Proper concrete mixes and finishing processes are the key to maintaining surface strength and preventing scaling.


Discoloration can appear as stains, spots, or blotches in the concrete. Discoloration has no single cause. Chemical variations like calcium chloride admixtures or cement alkalis can lead to discolored areas. Alternatively, factors like a hard-troweled surface, a wet substrate beneath the slab, or a change in the water-cement ratio at the top of the slab can lead to stains or patches. Discoloration can also occur long after the construction of the slab. In this case, the problem is usually superficial, and property owners can take care of it with power washing techniques. You can prevent discoloration by following best practices for mixing, laying, and finishing concrete. That said, this defect doesn’t cause any structural damage. If the slab isn’t exposed, it won’t cause any issues.

Low Spots

Low spots are exactly what they sound like: dips in the concrete that ruin the flat, even surface of your slab. These spots prevent your slab from draining properly and can create an uneven surface for construction. Like most other defects on this list, low spots are a symptom of improper laying and finishing. Poor lighting, improperly set forms, overly wet concrete, or mistakes during finishing can create low spots. By avoiding these issues and following best practices during construction, you can avoid low spots and create an even, functional slab every time.


Pop-outs occur when fragments of concrete break off and leave a hole in the slab. These flaws vary in size and are usually conical in shape. They usually occur when a piece of porous rock absorbs moisture and swells. This creates internal pressure that eventually breaks the surface of the concrete and forces the broken fragment out. In addition to creating an uneven surface, the holes left behind create problems with draining. They can also allow debris to get into the concrete slab and cause more damage. You can help prevent pop-outs by using concrete mixtures with low water content, choosing crushed-stone or beneficiated-aggregate concrete, and letting the concrete bleed before finishing.

The more you know about these common concrete problems, the easier it is to prevent or fix these issues. In addition to this knowledge, you need the right equipment on your side. If you’re in the concrete business, make sure you have a rig that can perform your work effectively and efficiently. Mobile spray foam rigs and other equipment from Spray Foam Systems help you get the job done right. With high-quality results and satisfied customers, you can take your contractor business to the next level.

The Most Common Concrete Slab Defects

Great Products Made Simple