Scaling is when the surface of a hardened concrete slab breaks away from the slab to a depth of about one-sixteenth to three-sixteenth of an inch. This usually occurs at an early age of the slab. There are four principles causes. The first cause is early cycles of freezing and thawing of the surface of newly placed concrete. To prevent this, keep the temperature of freshly placed concrete above 50 degrees F. for at least 5 days. The second is cycles of freezing and thawing when non air-entrained concrete was used. The third is applications of deicing salts when non air-entrained concrete was used. Both these problems can be solved by using air-entrained concrete. The fourth cause is faulty workmanship. This can be prevented by never allowing finishing operations to be performed while free water is present. Crazing is the occurrence of numerous fine hair cracks in the surface of a newly hardened slab due to surface shrinkage. These cracks form an overall pattern similar to a crushed eggshell. There are three causes of crazing. One, rapid surface drying usually caused by either high air temperatures, hot sun or drying winds. If any of these conditions are present, apply a fog spray or cover with burlap or canvas immediately after screeding and darbying. Two, premature floating and troweling. Never start floating and troweling until excess moisture has evaporated from the surface and the concrete has started its initial set. Three, overuse of the jitterbug, vibrating screed, darby or bull float. It is important, therefore, to use these tools sparingly. The appearance of a powdery material at the surface of a newly hardened concrete slab is called dusting. Dusting has six major causes. The first is an excess of clay or silt in the concrete. To prevent this use clean and well graded coarse and fine aggregate. The second is premature floating and troweling. You should delay floating and troweling until all free water or excess moisture have disappeared and concrete has started its initial set. The third is carbon dioxide from open salamanders or gasoline engines, power buggies or mixer engines. Therefore, because of the effect of the fumes on concrete, vent salamander fumes to the outside. The fourth is condensation on the surface before floating and troweling operations have been completed. If possible, this condition of condensation should be anticipated and the concrete should be heated, or at least hot water should be used for mixing. The fifth is dry heat from winter protection heaters will lower the relative humidity around the concrete excessively. Because of this, water jackets should be placed on heaters to increase the relative humidity by evaporation and any one of the acceptable methods of moist curing should be employed. The final one is no curing or inadequate curing. It is essential to properly cure for the specified length of time .