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Why Concrete Cracks and How to Prevent Further Damage

Concrete cracks are extremely common, and at times can be inevitable. The American Concrete Institute states in ACI 302. 1R-04 in part “even with the best floor designs and proper construction, it is unrealistic to expect crack-free and curl-free floors.” Cracks can be caused by deformation, hydraulic shrinkage, thermal shrinkage or swelling. Filling cracks not only makes your hardscape look better - it prevents common issues like moisture, insects, and damage from seeping through. When cracks are left as is water can further deteriorate the concrete and cause more severity to the problem.

Common Causes of Concrete Cracks

Improper installation:

Slabs can shrink ½ inch per 100 feet. The more wet the concrete mix, the more it will evaporate and shrink. Shrinking causes forces to pull apart, resulting in cracking. Shrinking can be caused by:

  • Excess water in mix: Adding too much water reduces the strength in concrete and requires more evaporation causing shrinkage and cracking.

  • Rapid Drying: The bond in concrete is created as water evaporates. When it dries too fast the concrete will shrink and cause cracks.

  • Inadequate strength concrete: Not all concretes are made the same. Concrete is available in a range of strengths for various environments. High traffic areas and anticipated shifting require a more concentrated bond for high strength and durability.

  • Lack of control joints: Control joints are used to relieve stress by anticipating and controlling where the concrete cracks.

Cracks caused by swelling

Swelling causes pressure pockets to form inside the concrete, eventually resulting in cracks.

  • Chemical reactions: Concrete can swell from salts like sulfates, a natural mineral in the earth that can be in contact around the slab.

  • Water freezing: Cement is naturally porous, allowing water to flow freely. During freezing moisture trapped inside will expand up to 9%.

  • Oxidation: Concrete cracks as it’s oxidized. When cracking occurs, it accelerates the oxidation process, causing more cracks.

Types of concrete cracks

  • Hairline: Surface level cracks that do not cause structural problems.

  • Floor: Floor concrete slabs with cracks are common and usually not structurally damaging. Floor cracks leaking is often caused by hydrostatic pressure or a high-water table. Sealing the crack redirects the pressure elsewhere, so it is important to find the source of those problems beforehand.

  • Shrinkage: Cracks that form as a result of concrete shrinking.

  • Settlement: The ground beneath the slab wasn’t compacted properly causing concrete to shrink.

  • Structural: Wider than 2” and/or runs through entire slab. Cracks wider than 2” are usually a sign of a more serious underlying problem.

Choosing concrete repair product

Concrete cracks must be repaired with a concrete repair mix, it cannot be repaired with regular concrete. Traditional concrete repair options on the market are epoxy, latex patching material, and mortar mixes. These solutions are wet applications, making installation tedious and potentially messy.

ConSANDtrate Dry Crack Filler is a flexible, polymerized concrete suitable for narrow and large crack fill. Dry application makes installation clean and easy. Simply fill cracks, activate ConSANDtrate - Intelligent Bond Technology by misting with water, and allow to dry. Mixed grain size aggregate permeates cracks, insuring cohesive bonding throughout. When exposed to water, ConSANDtrate begins to bond and as water evaporates it cures to form a hardened infill similar to concrete.


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