Even the most carefully poured and finished concrete can develop defects. Concrete surface defects can range from minor blemishes to major structural problems, compromising the concrete’s integrity. This is why it’s important to repair concrete surfaces.
Types of Concrete Surface Defects
Some common surface defects include cracking, crazing, delamination, scaling, and spalling. These defects can occur when the concrete is exposed to various factors, including improper mixing, finishing and curing procedures, extreme temperatures, moisture, or chemicals.
Cracking is one of the most common concrete surface defects. It can occur in a variety of patterns, including shrinkage cracks, settlement cracks, and structural cracks.
The natural drying process of concrete causes shrinkage cracks, while settlement cracks occur when the concrete settles due to the subgrade beneath the concrete is not properly compacted. Overloading or inadequate reinforcement can cause structural cracks.
Frequently a sign of excess moisture from sand and water in the concrete, efflorescence is a white, powdery substance that appears on the surface of concrete. The salt migration, where they react with moisture and air, causes concrete blemishes.
Honeycombing is a defect that occurs when you don’t correctly consolidate the concrete during placement. It results in voids or pockets of air within the concrete, weakening the structure and reducing its durability. Proper vibration along the forms should remove the air and prevent honeycombing.
Dusting occurs when the surface of concrete becomes weak and powdery. Over-troweling causes the surface to become too smooth and prevents proper bonding. Excess moisture in the concrete can cause dusting, weakening the surface and deteriorating it.
Voids are empty spaces or pockets within the concrete that can weaken the structure and reduce its durability. Improper compaction, poor consolidation, or inadequate curing causes voids, including improper formwork or the presence of foreign materials.
Often triggered by freeze-thaw cycles, scaling happens when the surface of concrete flakes or peels away, causing the surface to expand and contract. The use of improper curing methods or the presence of excess moisture causes surface scaling.
Similar to scaling, spalling occurs when small pieces of concrete break away from the surface because of freeze-thaw cycles.
When the surface of concrete becomes discolored, staining takes place. Various factors, including exposure to chemicals, minerals, or other substances, cause this defect.
Bugholes are small, irregular cavities that appear on the surface of concrete. The entrapment of air bubbles causes them during the placement and compaction of the concrete. Bugholes can be minimized using proper vibration techniques and ensuring the concrete is properly mixed and placed.
Sand streaking on the formed surface is a defect that occurs when the surface of concrete becomes discolored due to the presence of sand particles. Improper finishing techniques make the sand particles rise to the surface.
Using proper finishing techniques can minimize sand streaking.
Blistering is a defect that occurs when small bubbles or blisters appear on the surface. The presence of excess moisture within the concrete makes the surface become weak and porous. Poor curing methods or poor quality materials (or foreign materials) may result in blistering.
What Causes Concrete Defects
Surface defects can occur for various reasons, including improper mixing, finishing, or curing and environmental factors such as temperature and moisture. This section will explore some common examples of what can cause defects.
Inadequate curing is one of the most common causes of concrete surface defects. Concrete not appropriately cured can lead to cracks, crazing, and shrinkage. Inadequate curing can be caused by not providing enough moisture, not covering the concrete with a curing blanket, or removing the curing blanket too early.
Poor workmanship during the placement of concrete mix can also lead to surface defects. This can include improper finishing techniques, not using the correct tools, or not following the correct concrete placement procedures or not allowing it to harden. Poor workmanship can cause rock pockets, honeycombing, and cracking.
Improper application can include:
- Not using the correct amount of concrete.
- Not placing and compacting the concrete properly.
- Not using the correct mix design.
Improper surface treatment application can cause low spots, scaling, and popouts.
Incorrect Mix Design
Using the incorrect mix design includes using too much water, not using enough cement, or not using the correct aggregate. As mentioned above, improper mix design can lead to crazing, scaling, and spalling issues.
Vibration consolidates concrete, a crucial step to ensure its strength and durability. Insufficient vibration means not using the correct vibrator, not vibrating the concrete adequately, or not vibrating the concrete at the right frequency. Such oversight can result in issues like honeycombing, rock pockets, and cracking.
Early Formwork Removal
Removing the formwork or reinforcing bars too early can also lead to surface defects in concrete. This can cause issues such as cracking and crazing. Following the correct procedures for removing formwork is vital to avoid these issues. In addition, air pockets and bolt holes can form if the concrete is not carefully packed.
How to Repair Concrete Defects
Repairing concrete defects involves removing and replacing the concrete with good material.
This requires several steps, including inspection and assessment, surface preparation, application of repair mortar, and painting and sealing.
Here is a brief overview of each step:
1. Inspection and Assessment
The first step in repairing concrete defects is to inspect and assess the extent of the damage. A professional engineer or contractor who can identify the cause of the fault and determine the best course of action can do this step.
Moisture, corrosion, and reinforcing steel issues are common causes of defects in concrete structures.
2. Surface Preparation
Once you’ve identified the cause, the next step is to prepare the surface for repair. This involves removing any loose or unsound concrete and cleaning the surface thoroughly. Before applying the repair mortar, the surface should be free of any debris, oil, or grime.
3. Application of Repair Mortar
After preparing the surface, apply the repair mortar. The type of repair mortar used will depend on the type of defect and the extent of the damage.
For example, if the defect is honeycombed, fill the voids with grout. If the defect is more severe, structural concrete can repair the area.
4. Painting and Sealing
Once you apply the repair mortar, the final step is to paint and seal the surface. This will help prevent further damage and protect the surface from the elements. The type of paint and sealant used will depend on the defect type and the structure’s location.
How Wide Is the Crack?
How you go about fixing the crack may depend on its current size. Very small cracks may only require liquid filler or caulk to repair them.
However, cracks larger than 1/8” may require something a bit more substantial. Look to solutions like skim coats for concrete crack reparation for these cracks.
How to Fix Uneven Concrete
You can use light-duty resurfacing products for a less demanding leveling issue. You also may need to grind the floor to flatten and smoothen the surface, depending on the space and context of the concrete.
With the right tooling and horsepower, you should have the surface flattened and ready for foot traffic in a reasonable amount of time.
When repairing concrete, you can only get as far as your tools allow.
Equipment and accessories that you may need when you repair a concrete crack include:
- Hammer and masonry chisel
- Wire brush
- Pressure washer or garden hose
- Concrete compound
Preventing Concrete Floor Defects
Another step to repair is prevention. Identifying and addressing defects early on is crucial to preventing further damage and ensuring the long-term durability of the concrete.
Moisture is a pretty notorious enemy of concrete. You should take measures to ensure unwanted moisture is avoided in your space or upon installation or you risk surface cracks (or worse).
You’ll also want to ensure you’re mixing the concrete adequately. Concrete not mixed well will not form a good bond and, therefore, be weak once set and dried.
Another way to prevent concrete surface issues: hire a professional.
Suppose you’re a home or commercial property owner attempting to apply concrete surface solutions with little or no experience in the practice. In that case, you risk missing out on the informed and careful approach that comes from workers with seasoned backgrounds.
At Runyon Surface Prep, our team of experts is ready to provide the insights, equipment, and materials you need to ensure your project’s success.
Don’t compromise on quality or expertise.