CoatingsPro Magazine

MAY 2015

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 39 of 92

COATINGSPRO MAY 2015 39 repair procedures can be per for med. Dy namic cracks quite often can be complicated to repair. T he location oftentimes w ill tell you why the crack occurred. Excessive shr inkage cracks in a properly cut slab is an indication that the concrete could have poor tensile strength from improper cur ing or a high water/cement (w/c) ratio. Cracks emanating from the cor ner of columns, pit angles, cor ners of wa lls, around f loor drains, and other slab penetrations are usua lly static shr ink- age cracks. Crack identification is the first stage of a crack repair procedure. T he pur pose of the contraction joint is to prevent cracking. A crack close to a contraction joint may be an indication that there was a problem w ith the concrete when it was placed. Further testing or investigation needs to be done. In one particular f loor, it was discovered that the concrete finisher did not follow the specification. He ordered concrete w ith a high w/c ratio and did not wet-cure the slab. Crazing is a surface defect that is generally caused by poor or improper curing procedures. Crazing is an array of very fne, shallow cracks similar in appearance to mud cracking. Generally, it does not pose any structural issues with the concrete. Te presence of crazing, though, could be an indica- tion of high permeability within the concrete. Hardness of Concrete T he hardness of the concrete needs to be determined in order to apply coatings. Soft, punky concrete has a lower tensile strength that equates to lower bond strength. Hard, dense concrete usually has a higher tensile Evaluating the depth of the contamination into the concrete is important. Some contaminants will penetrate well below the surface, making them very difcult to remove. Inspector's Corner Wr i te in Re ad e r In q u ir y #266

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