We recently put in a 40- by 120-foot industrial floor. No curing membrane was applied because the weather was cool and damp. The owner complained because we didn't cure and didn't put in joints. We offered to saw joints for an additional charge but he elected not to pay for having us do the sawing. Cracks have formed across the floor wherever there are columns, which are located every 20 feet along the long sides. Was the cracking caused by failure to cure?
Failure to cure was a serious mistake that will reduce the strength and wear resistance. It is just as bad for strength to omit curing as to leave out one or two bags of cement per cubic yard. Whether the concrete was cured properly or not, however, it would undergo some shrinkage as it dried out. The normal shrinkage in floors is enough to cause a crack to form every 15 to 25 feet. For this reason control joints should be intentionally provided ahead of time at intervals of about 15 to 25 feet to provide the needed relief. If the contractor does not provide his clean joints at such intervals nature will provide its ragged ones. It is likely that in this 40-foot wide floor there will eventually be another crack or two running lengthwise. In addition to control joints, isolation joints should be provided around all columns and other points of restraint.