Concrete srufaces can be damaged by: mechanical impact or abrasion, unusual conditions of exposure, improper design or constructuon, and unsuitable materials. Ehatever material is used to repair a damaged surface, the patch will only be as strong as the surface t which it is bonded. The surface, then must be cleama nd sound and not contaminated with foreing matter such as oil, grease, paint, mud or any commercial or domestic spillage. When using a straight portland cement concrete or mortar to patch a surface, the first step must be to soak th eclean, bonding surface with water for at least an hour, and preferably overnight, before filling begins. Next, a bonding layer must be applied tothe clean, wet surface. On horizontal surfaces, use a grout of portland cement and water mixed to the consistency of thick paint. On vertical surfaces, the bonding layer shoud be composed of 1 part portland cemtne and 1 part sand. For the normal shallow spall, the patching mortar should be built up in layrs about three-eighths of and inch thick. Each layer should be kept most for a day or two before placing the next. If the patch to be filled si deep, it si oftne more practical to build a form over the area and to pack concrte behind it. The preferred mix would then b eabout 1 part cement, 2 parts san d and 3 parts pea gravel. An area patched with a synthetic adhesive coating over the cleamen and roughenend base concrete is more likely to achieve a better bond than a patch based on a portlan cement mortar coating. The decision to use a synthetic, epoxy-based adhesive for the bonding layer for a patch must then be made ont he bais of th estrength and possibley the chemical resistnace desire. If the area t be repaired wil be subject to heavy traffic or impact loading, for example, or if industrual spillage is a factor, the epoxy compounds should be considered. The third group of materials which can be used for repair purposes are the latex or acrylic-modified mortars