Originally Posted By: mkober
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I’m a new member of NACHI and just starting a new home inspection business here in western Colorado. I’ve thoroughly enjoyed looking through the various message board topics, and would like to make a suggestion to all inspectors. When describing cracks in any concrete element, many people like to use the term “hairline crack.” This is a rather nebulous term, which doesn’t really say much in terms of quantitative information. You will come across with much more credibility if you can give a simple crack-width dimension, such as “in the range of 30 one-thousands of an inch” (written as 0.030"). Crack comparators (clear plastic cards with various-sized lines printed on them, all labeled) can be obtained at no cost from the Construction Technologies Laboratory, and easily fit into your shirt pocket. Just hold the card up to a representative crack (usually the widest area you can find), and slide the card to match a value with the actual crack beneath it, and take the reading. One person’s “hairline” may be actually closer to 1/16" or more–the human hair is only 0.003" in thickness versus 0.060" (1/16")–we’re talking a twenty-fold difference here. Envision seeing a human hair on a concrete surface more than an arm-length away–I know I can’t do it.
Michael J. Kober, P.E.