Any emergency demands a fast response; concrete waits for no one. Only the contractor's ingenuity or foresight can rescue some projects from failure. A few examples follow. A power failure on a crane or materials hoist during placing can interrupt concreting long enough to produce a cold joint. Most large jobs require alternative methods for moving concrete to its final location. If pumps are used as alternatives, suitable proportions for the pumping mixes should be prepared ahead of time. These proportions can be furnished by the ready mixed concrete supplier. On jobs that don't require elevating the concrete, a few wheelbarrows can serve as a standby means of finishing out a section of slab- but only if the contractor has had the foresight to provide them. A sudden thunderstorm can dump enough water on slab under construction to ruin it. Polyethylene sheets should be kept on hand for emergency covering of any floor. Floor finishers may need portable shelters during prolonged rains. The polyethylene can be removed from small areas of the floor while the finishers work. Superficial frost damage to the surface can sometimes be repaired by skimming and grinding. The skimming is done with a mixture of latex, fine sand, and portland cement. The resulting surface may be slightly less wear resistant than an undamaged one might have been. Another method involves grinding the floor with terrazzo grinders, filling hoes with portland cement after the initial grinding and cleaning.