INTRODUCTION
Cracks in concrete are common and it if often misunderstood as not having done mixing properly or compaction properly or problem in foundation and many more. In general cases cracks sizes ranging from 1/4 inch to 1/16 inch is considered to be acceptable limit. One can control cracking by properly preparing the subbase, proper curing, not favouring under-reinforcement or over-reinforcement, by proper placing and spacing crack control joints, etc. To fix narrow cracks in concrete, caulk-style concrete repair compound is used because of its easy application. For larger cracks especially in case of walls, epoxy injection kit is used which allows deep penetration through cracks. In case of repairing of stairs, vinyl concrete patcher is used as it is durable and easy to mould into a step like shape.
Causes Of Cracks In Concrete
Although exact cause cannot be stated, some estimations can be made by looking at the size and shape. Some causes are-
1. Some masons use lot of water to make the mix easy to handle in building constructions. They don’t give importance to strength criteria rather they give importance to workability criteria. This leads to low strength in concrete and as a result cracks appear. Shrinkage is another common reason for cracking. As concrete hardens and dries it shrinks to a great extent. This occurs due to the evaporation of excess of mixing water.
2. Rapid drying of slab leads to cracking of concrete. In some building projects rapid drying is preferred as per the requirements of building contract schedule. Hence negligence is one such cause.
3. Lack of control joints is one such cause. The joints should be of the depth of the slab and not more than 2 to 3 times (in feet) of the thickness of the concrete (in inches).
4. Foundations made during cold winter or cold places are often left unheated which leads to cracks.
Ways To Repair Cracks
1. Fixing a cracked floor-
- Using a caulk style waterproof compound is proved to be effective here. It is the best choice for hairline cracks smaller than 1/4 inch.
- Loose concrete or debris are removed using wire brush. Also, a small hammer and chisel can be used in this case.
- Vacuum cleaner or sweeping brush or broom is used to blow away remaining dust. A canister of compressed air can also be used to blow away fine surface debris.
- Then a bead of epoxy concrete repair compound is run along the crack. This involves loading a cartridge of liquid concrete repair compound into the cradle of a caulk gun. After that we snip about 1/8 inch off the tip, then we run a continuous bead of compound along the crack. For a crack wider than 1/4 inch we slide in a strip of foam backer rod with fingers. Then we apply concrete repair compound with the caulk gun over the rod.
- Then the caulked surface is made smooth and cured for 4 hours to 6 hours. After smoothing the compound, putty knife is wiped promptly with mineral spirits before the epoxy begins to set.
2. Sealing a wider crack in wall –
- 2-part epoxy (an unmixed compound), caulk-type epoxy cartridges, liquid concrete repair injection ports are used in this case. These injection ports have small nozzles that help in filling deep inside the crack with sealer.
- Then loose debris or chunks of mortar, concrete, etc. are scrubbed away with a wire brush or hammer and a chisel.
- Vacuum cleaner or broom is used to blow away remaining dust or minute particles.
- Then finishing nails of particular sizes are pushed in cracks with hammer in every 12 inches. Separate sticks or putty knives are used to scoop the 2 epoxy parts onto a small scrap board. The parts are mixed until a uniform colour is achieved. Then small dabs are applied to the bottoms of the ports, and a port is slide over each nail.
- After installing the port, the tip of the nail is grasped and pulled out making sure the ports are glued and not pulled out along with nail.
- A larger batch of the compound is mixed as directed. A putty knife or trowel is used to cover the crack. The compound is spread on either side of the crack, and levelled it with the surrounding surface
- The surface patch is let to cure for around 4 to 6 hours, then the injection ports are filled.
- The injected compound is allowed to cure for 5 days, or as per instructions. Then a hacksaw is used to cut off the ports’ nozzles.
3. Repairing cracked concrete steps-
- Vinyl concrete patcher works best on wider cracks in case of horizontal surfaces hence it’s perfect for broken steps. It is needed to apply it in 1/4 to 1/2 inch layers and each layer is allowed to cure before the next application.
- The surface is prepared by scrubbing or chiselling away loose concrete or deposits of old filler. A wire brush is also used to rough up any smooth surfaces within the crack. Then remaining dust is cleaned by sweeper or vacuum cleaner.
- The hose is made to run evenly over the steps to get the surface damp.
- A wood plank is placed against the cracked step to create a frame. This plank will act as a form and ensure the repair compound to take the shape of the step.
- Ready to mix patches need no water. While they are more convenient, they are more expensive than dry products, which we mix with water.
- A trowel is used to apply the vinyl concrete patcher. It is recommended to clean the tools with water immediately after applying patch.
- Then the wood plank is removed after the patch has set.
- Then the patch is allowed to cool for 24 hours or until set.
Conclusion
While adopting epoxy and urethane-based concrete repair compounds, it is advisable to use gloves as they are very sticky. Furthermore, cracks in concrete can be reduced to a great extent by using reinforcing wire mesh, synthetic fibres or rebar. Also, it is not permissible to use too much steel as it can cause cracking by restraining normal shrinkage of concrete. It is sometimes not possible to determine the exact cause of concrete but efforts can be made to reduce it by good site preparation, adopting good finishing practices and more planning of the building project.
References
- Ardex, “Why Concrete Cracks”- https://www.ardexbuildingproducts.ie/why-concrete-cracks/
- Concrete Supply Co., “6 Types of Concrete Cracks and What They Mean”- https://concretesupplyco.com/6-concrete-cracks/
- The Balance Small Business, “How to Repair Wide Cracks in Concrete”- https://www.thebalancesmb.com/is-this-the-best-way-to-repair-concrete-cracks-844642
- Wise Cracks, “5 Reasons Why Concrete Cracks”- https://www.wisecracks.com/5-reasons-concrete-cracks/
- Wikihow, “How to Fix Concrete Cracks”- https://www.wikihow.com/Fix-Concrete-Cracks#Repairing-Cracked-Concrete-Steps
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