Paradoxical though it may seem, water is the chief enemy of concrete, even though it plays such a vital role in the hydration of the cement in concrete and in moist curing. If water penetrates the surface and then freezes, it can easily spall off the surface of the concrete. In addition, it can carry harmful chemical solutions into the concrete and bring some of the surplus lime out of the concrete in the form of efflorescence. Basically, seven types of protective coatings are discussed in this three part article. These are: (1) the cement based paints; (2) the silicone treatments; linseed oil; (4) bituminous coatings; (5) metallic compounds; (6) surface hardeners; and (7) plastic coatings. Cement based coatings usually consist of a mixture of white portland cement, silica sand, pigment when required, accelerators and water repellant. Since these coatings are cement based and are therefore inherently porous, they form a film that is continuous but can be put in the category of dampproofing only. They are not efficient water barriers. In general use, they are applied more frequently on interior surfaces than on exterior surfaces. They do have one advantage in that they allow the surface to breathe and therefore are not subject to vapor pressure which might build up behind the coating and break it loose. Silicone compounds are a very popular method of dampproffing exterior, above-grade walls. Silicone compounds are made by soaking silicone solids in a solvent solution. The material is sprayed onto the surface of the wall at a rate of approximately 150 square feet per gallon. The solution penetrates into the pores of the surface, the solvent evaporates and the silicone resin is left behind, forming a water barrier. Silicones, like the cement based coatings, are not a vapor barrier and therefore allow the substrate to breathe. This is important where there is insulation on the inside of the wall. The humidity of the material forming the wall can change from season to season without a possibility of the vapor pressure spalling off the exterior surface. Linseed oil contains up to 97 percent linseed oil and was made to readily emulsify with water. Two applications of linseed oil should be sufficient to protect concrete from winter damage. The oil penetrates the porous surface to a depth of approximately one-eighth of an inch and combines with the atmosphere to form a protective coating through which moisture and salt solutions cannot penetrate.