Concrete construction was once largely confined to paving and foundations. Today, it has been developed to the point where both large and small buildings are constructed entirely of concrete. Because of the long-lasting quality of concrete and its durability, it generally becomes a permanent fixture for the outdoor of a house especially for patios and walkways. Even with its durable quality, maintenance should still be done to keep it in good form. Concrete patios and walks should be inspected regularly for dusting, spalling, cracking, and settling. Patios and walks constructed of concrete require comparatively little maintenance if the concrete mix hadthe proper composition and was correctly poured and cured. If they are exposed to severe abrasion, heavy vehicle loads, or similar wear conditions, however, they can develop problems. One of the more common problems with concrete floors is the development of unsightly cracks, which can also be caused by shrinkage, temperature changes, settlement, or lack of rigidity. When such movements are recurrent and can be eliminated only by major structural changes, little can be done except to keep the cracks filled with a mastic material. In many cases comparatively small cracks can be filled with varnish or resin. Although the cracks will remain visible, they will not leak or gather dirt. When the cause of larger cracks has been determined and corrective measures have been taken to eliminate further cracking, the cracks can be permanently repaired by filling them with non-shrinking cement mortar. Patching will not permanently correct cracks in slabs on grade caused by vertical movement resulting from exceeding the design load of the slab, inadequacy of the base, or insufficient bearing capacity of the soil. Slab failure under these circumstances can be corrected only by a major maintenance operation, such as mudjacking. Surface cracks that are not structural defects must be promptly filled to maintain a watertight surface. Thoroughly clean the crack with a high-pressure water jet to remove all foreign matter. Edges of the crack should be moistened but not wet. Fill the crack with a thin grout of cement and water, using a brush if necessary to push the grout into the crack. For wider cracks, use a mortar of cement, sand, and water instead of cement grout. If cracks are not wide enough to permit placement of filler material, they should be cut out prior to cleaning. After filling the crack, cover it with burlap or sand, and keep the covering moist for three days.