How to Repair Hairline Cracks on a Concrete Surface?

As per ACI 116R-90, in civil engineering structures and construction, a hairline cracks are defined as cracks that are observed in exposed concrete surface whose width is very less that is barely distinguishable. In general, it can be categorized as cracks in concrete that has width lesser than 0.003 inches or 0.08 mm. 

Now, once you identify a hairline cracks, the second important thing to be investigated is the cause of the crack. Based on what causes hairline cracks, the depth and width of the crack varies.
How to Correct Hairline Cracks on a Concrete Surface?

How to Repair  Hairline Cracks in Concrete Surface?

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The basic steps involved in the correction of hairline cracks are:
  1. Cleaning the Cracked Surface and Cracks interior
  2. Making the cracks moist
  3. Preparation of sealant to fill the hairline crack
  4. Application of sealant into the cracks
  5. Curing of cracks

1. Cleaning the Cracked Surface and the Crack Interior

The hairline crack area is properly cleaned to remove any stains or dirt on the crack area. Before applying the filling material, any external matter that have covered the concrete surface must be cleaned.

2. Making the Cracks Moist

The hairline crack on the old concrete surface must be moisten with water around 7 hrs before the application of grout or filling material into the crack. Moistening the crack area, helps to prevent the drawing of water from the applied grout. If this happens, the grout will dry out without sealing the crack. Moistening the crack does not want water to stand or clog the surface and the crack.

3. Preparation of sealant to Fill the Crack

Usually the most common grout used is portland cement and water mix. Sufficient water is added to make a good grout mix. Other that cement grout, any other sealant or filler material can be used to fill the hairline crack. An ideal sealant must posses low viscosity and surface tension. These properties help the sealant to penetrate into the crack depth completely.

4. Application of Sealant into the Cracks

After the hairline cracks have been moistened, it is cleaned and grout is applied either using a putty knife or a pointing trowel. The ground need to forced into the crack as much as possible. Excess amount falling out is smoothened and levelled to the original concrete.

4. Curing of Cracks

The sealed cracks must be patched dry for around 2 hours and covered using a plastic sheet or a board. It must be kept covered for around 5 days. Each day the covering must be lifted and water need to be sprinkled with water.

Note: Hairline cracks are rarely a great concern. It can only be controlled and its tough to eliminate. It can be minimized some important construction practices. Also Read: How to Prevent Hairline Cracks in Concrete Surface?

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