How to Repair Concrete Cracks

This article will discuss different types of concrete cracks. After finishing the article, you will know how to repair concrete cracks. Concrete cracking has been an oft-discussed topic. We have compiled a group of construction tips to help towards preventing cracks, and tips regarding cracking.

Concrete consists primarily of cement, sand, gravel and water. As the water in the slurry evaporates, the remaining ingredients cure into a hard, monolithic slab. Unfortunately, the curing process causes the concrete to shrink slightly, often resulting in hairline cracks. Larger stress cracks occur when a house settles or the ground beneath it shifts. These types of cracks typically don't threaten the structural integrity of the house, but they do create an entry point for groundwater, insects and radon gas. Here, we'll show you a simple, effective way to patch cracks in poured- concrete walls.

If you notice large, recurring cracks or bulging walls at your house, don't try to fix these conditions yourself. The cracks might indicate a more serious structural problem; call in a structural engineer for an in-depth evaluation.

Some Common Reasons for Concrete Cracks
1. Uneven evaporation of moistures: The uneven evaporation of moisture from concrete causes various types of cracks. If the water evaporated from the surface of the freshly placed concrete faster than it is replaced by the bleed water, then plastic shrinkage cracks appear. The excess moisture left out after hydration is eventually evaporated and causes the concrete to shrink, but the shrinkage is resisted by subgrade, reinforcements, and the other parts of the concrete, causing drying cracks.

2. Thermal Cracks: The inner temperature of the concrete increases due to the heat of hydration in the concrete. This temperature difference between the core and the surface causes thermal cracks.

3. Corrosion: The volume of the rust is always greater than the volume of steel. So, if the reinforced steel becomes corroded, then it exerts force that causes concrete cracks.

Steps for Repairing Concrete Cracks
  1. Clean It: Remove all the loose dirt by using a chisel and light hammer or maybe by using only a chisel. Use a broom or small brush to clean the surfaces neatly. The idea is to make the crack surfaces hard and clean enough so that chemicals can be applied directly to the crack surfaces.
  2. Wash it: Clean the cracks with water and use washing powder. You can use a hose to spray the water. Remember that the cleaner the surface, the greater will be the strength of the repaired concrete.
  3. Dry it: Leave the clean crack surfaces for drying. You can use a cover during drying in case of a dirty environment.
  4. For Small Cracks: Use the ready-made concrete repairing compounds. Prepare the compound as directed. Use a small chisel or a knife to prepare the crack. Pour the concrete repairing compound into the crack and use the chisel or knife to force the compound paste into the cracks. Once filled, smooth the surface and cover it up. Leave it for complete drying.
  5. For Large Cracks: Use readymade fortified concrete; there are various manufacturers available. Read the application directions carefully for the product you will use. The fortified concrete will be of powder form and you have to just apply water in it. Remember, once you add water the mixture should be consumed as quickly as possible, so make a small batch, sufficient enough for a single layer, at a time.
While concrete cracks appear to be typical, it is not recommended that they remain ignored. Most homeowners best identify concrete cracks in their basement, either on the foundation wall or on the floor. They may also recognize cracks on the garage floor, patio or in-ground pool.

These cracks typically due to drying shrinkage, thermal movement or other causes usually are minor and result in few problems. More often than not, a foundation crack will widen over time and result in water seepage or possibly the loss of structural integrity. Foundation and slab cracks are not only an eyesore, but they may hinder the value of the home.

When installed properly, concrete is one of the most durable and long lasting products you can use around your home. But it is important that concrete contractors follow well-established guidelines with respect to concrete placement. Durable, high strength, and crack resistant concrete does not happen by accident.

Why Concrete Cracks
1 - Excess water in the mix
Concrete does not require much water to achieve maximum strength. But a wide majority of concrete used in residential work has too much water added to the concrete on the job site. This water is added to make the concrete easier to install. This excess water also greatly reduces the strength of the concrete.

Shrinkage is a main cause of cracking. As concrete hardens and dries it shrinks. This is due to the evaporation of excess mixing water. The wetter or soupier the concrete mix, the greater the shrinkage will be. Concrete slabs can shrink as much as 1/2 inch per 100 feet. This shrinkage causes forces in the concrete which literally pull the slab apart. Cracks are the end result of these forces. The bottom line is a low water to cement ratio is the number one issue effecting concrete quality- and excess water reduces this ratio.

What you can do about it:
Know the allowable water for the mix the contractor is pouring- or be very sure you have chosen a reputable contractor who will make sure the proper mix is poured. It is more expensive to do it right- it simply takes more manpower to pour stiffer mixes.

2 - Rapid Drying of the concrete
Also, rapid drying of the slab will significantly increase the possibility of cracking. The chemical reaction, which causes concrete to go from the liquid or plastic state to a solid state, requires water. This chemical reaction, or hydration, continues to occur for days and weeks after you pour the concrete. You can make sure that the necessary water is available for this reaction by adequately curing the slab.

3 - Improper strength concrete poured on the job
Concrete is available in many different strengths. Verify what strength the concrete you are pouring should be poured at. Talk to the ready mix supplier Consult with the Ready Mix Concrete Association in your area.

4 - Lack of control joints.
Control joints help concrete crack where you want it to. The joints should be of the depth of the slab and no more than 2-3 times (in feet) of the thickness of the concrete (in inches). So 4"concrete should have joints 8-12' apart.

Other reasons:
  1. Never pour concrete on frozen ground.
  2. The ground upon which the concrete will be placed must be compacted.
  3. The sub grade must be prepared according to your soil conditions. Some flatwork can be poured right on native grade. In other areas 6"of base fill is required along with steel rebar installed in the slab.
  4. Understand what you contractor is doing about each of the above listed items and you will get a good concrete job.
The size of the concrete cracks decides the method used to repair concrete cracks. For critical concrete cracks (like cracks in foundations, etc.) it is advisable to seek professional help.

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