Hairline crack in sidewalk slab

Old 09-12-13, 08:17 AM
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Join Date: Jul 2007
Location: USA
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Hairline crack in sidewalk slab

In June, 2010, we had our back steps replaced. As part of the job, two slabs of concrete at the base of the steps were also replaced.
Yesterday, I noticed a hairline crack had formed across the entire width of one of the slabs. My bother in law suggested that I "seal it". My question: should I? and with what?

My current plan is to keep an eye on the crack, and to see if it widens or deepens.
Any suggestions?

(I took a picture, but it is "too large a file" to upload" .
Old 09-12-13, 12:25 PM
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Join Date: Oct 2011
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If it's truly a "hairline" crack, then it's not practical to seal it. A human hair is about 0.003" in diameter; if you place a human hair on the concrete next to the crack, are they both about the same size? In general, most low viscosity epoxies suitable for injection of tight cracks only work if the cracks are wider than 0.005".

The sidewalk probably cracked because of thermal movement, combined with a lack of control/contraction joints--which should have been installed when the concrete was placed, using a grooving tool in the wet mud or sawcutting just after initial set.

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