How to Prevent Cracks in Concrete

If you are planning a concrete project, you will be dedicating your time and money to making it perfect. Whether you will be doing the job on you own or hiring a contractor, there are a few things you should think about before getting started. While it is impossible to guarantee that your newly poured concrete will not eventually form cracks, with a few simple tips you can prevent damage.

Difficulty: Moderate

Instructions

Pouring the Concrete

1. Know ahead of time how much water should be mixed into your type of concrete mix. Adding water makes the concrete spread further for an easier pour. But as the water evaporates from the mix, the concrete hardens, dries and shrinks. The more water that is added, the more the concrete will shrink, and the more it will crack.

2. Pour concrete on compacted subgrade to prevent cracking. If the subgrade is not compacted, the soil, and concrete above it, will settle and cause the slab to crack. Most rental companies have equipment available to properly compact the subgrade, and it is well worth the investment.

3. Cut control joints into the concrete so that the slab will be able to shrink and expand with temperature changes. Control joints should be cut the same depth of the slab and spaced a maximum of three times the thickness of the concrete. For instance, if your concrete slab is 4 feet, you should have control joints spaced about 12 feet apart. All control joints should be cut between 6 and 12 hours after pouring the concrete.

4. Cure the drying concrete slab properly to prevent rapid drying and cracking. The slab must retain enough moisture so that the drying and shrinking happens as slowly as possible in the days and weeks after pouring. This increases the final strength and water resistance of the concrete.

Curing the Concrete

5. Flood the slab regularly with water or spray mist over the slab several times a day beginning about 12 hours after the concrete begins to set, or after you have cut your control joints.

6. Cure the concrete by covering the slab with sand, burlap, straw or canvas that is continuously kept damp.

7. Apply a waterproof paper or a plastic seal to the concrete as soon as it is resistant to any surface damage. Plastic films can cause discoloration, so do not apply if the final appearance of the slab is important.

8. Use a chemical membrane cure as soon as the slab is finished. However, chemical curing compounds can later affect the ability for flooring to adhere to the concrete.

Tips & Warnings

• Curing with water is the most effective manner of preventing rapid water evaporation.