How to Prevent Cracks in Concrete Floors

Cracks in concrete are frustrating and unattractive.

Discovering cracks in your freshly poured concrete floor can be frustrating. Unfortunately, cracking occurs for many reasons and can happen to even the most skilled concrete pourer. When you're preparing to pour the concrete, however, there are a few things you can do to prevent the concrete from cracking.

Things You'll Need

• Water
• Concrete mix
• Sand
• Straw
• Canvas
• Burlap
• Waterproof paper
• Plastic seal
• Grooving tool

Instructions

1. Add the right amount of water to concrete mix. According to the Concrete Network website, one of the main causes of cracked concrete is too much water in the mix. Some add extra water to make the concrete easier to pour. Use a maximum of 50 percent water to cement ratio when the concrete is exposed to freezing and thawing in a moist condition. Use a maximum of 45 percent water to cement ratio for concrete with severe or very severe sulfate conditions.

2. Cure the concrete. Concrete that dries too fast is prone to cracking. Curing helps the concrete to retain moisture in the concrete so that it can continue to gain strength and it delays shrinking until the concrete is strong enough to resist cracking. Cure the concrete by flooding or misting it; using covers on it, such as sand, straw, canvas or burlap that is kept continuously wet or apply waterproof paper or plastic seals on the wet concrete.

3. Know what strength of concrete you need for your particular situation. The Concrete Network website states that improper concrete strength is a cause of cracking. Verify what strength you need by talking to your concrete mix supplier.

4. Pour concrete on ground that is not frozen. Pouring concrete on ground that is not compacted, such as frozen ground, can cause cracking.

5. Place control joints in your concrete. While control joints do not cause concrete cracks, they do help to control where they appear, if they do occur. These joints allow the concrete to move, based on changes that can occur due to temperature changes and drying shrinkage. Space joints no more than two to three times in feet the slab thickness apart. For instance, a 2-foot deep slab of concrete should have joints that are 4 to 6 feet apart. Use a grooving tool to cut the joints in fresh concrete and try to place the joints in areas that won’t be seen, such as under walls or carpet areas.

References

• Concrete Network: Why Concrete Cracks
• Concrete Network: Use a Low Water to Cement Ratio--How to Calculate Water to Cement Ratios
• Concrete Network: Properly Curing Concrete Slabs
• Concrete Network: Be Active in Deciding Where Control Joints Will Be Placed