construction of a sidewalk from concrete blocks.

Concrete projects often fail and the owner wonders why. Most mistakes that lead to failure are made during the mixing or pouring process. These mistakes might lead to flaking or deterioration and premature failure. What are some common mistakes to avoid?

Overly Wet Concrete

When concrete is properly mixed, it looks like it won’t flow and you won’t be able to trowel it. The concrete should easily be formable. If you can’t make a 4″ tall pile with a 4″ diameter, the concrete isn’t mixed properly.

Extremely Dry Concrete

Concrete that is too dry is also an issue. Portland cement is the basis for concrete, and this cement requires water to cure properly. When trowling the concrete, you should see a smooth, wet, and muddy surface after three swipes of the trowel. If you don’t, more moisture is needed.

Concrete Is Too Thin

Poured concrete is strong and durable when poured to the right thickness. Concrete slabs must be 4″ or thicker when used as a foundation for a small building such as a shed. Larger structures or those that receive heavy vehicle traffic must be 6″ or thicker.

Avoid using standard welded wire mesh to reinforce the concrete. This wire mesh won’t prevent cracking. It is designed to hold the cracked pieces in one place. Reinforcing fibers in the mixed concrete and reinforcing rods are the best way to prevent cracks from forming. Incorporate a pint of fibers into each mixing drum of concrete. The fibers will bind the hardened concrete.

Old Cement

Portland cement has an expiration date. After a year, you need to dispose of cement or just-add-water concrete mixes that have not been used. When opening a package of cement, look for lumps. Hard lumps are a sign the cement got damp, which minimizes its ability to harden.

Corrosion-Resistant Reinforcing Rods

Concrete is weak when outside forces attempt to separate it. To prevent this separation, contractors use metal rods to reinforce the concrete. However, bare steel rods may rust when water enters the concrete. Use galvanized, epoxy-coated, or fiberglass rebar to prevent rust formation and protect the project’s structural integrity.

Trowling at the Appropriate Time

Trowel the concrete once the surface water dries but the concrete remains soft and malleable. Completing this step early leads to surface water formation, increasing the risk of the surface flaking and failing over time. Delay this set and the surface won’t be smooth because the concrete hardened too much. The right time to trowel depends on the air temperature and the initial wetness of the concrete.

Skin Contact

The cement present in concrete is extremely alkaline. When this mixture comes into contact with the skin, injuries may occur. Many people get wet concrete on their hands all day and never notice any problems. However, when they get home, they notice thin or cracked skin on the hands that is red and painful. Wearing the appropriate gloves and only handling wet concrete with a shovel and trowel helps prevent this.

Air Temperature

Avoid pouring concrete when it is hot and humid outside. When temperatures reach 80 degrees Fahrenheit or higher, concrete hardens before it can be poured and troweled. Low temperatures also present a problem because the concrete will not be as strong if it freezes before it fully cures. This loss of strength puts the whole project at risk of early failure. Aim for moderate temperatures when pouring concrete to avoid these problems.

Pouring concrete isn’t easy. Many factors affect when and how this task should be done. Work with a professional if there is any doubt about handling this process correctly. You don’t want any mistakes when it comes to a project of this type.

Claire Preece