Masonry Magazine June 1968 Page. 24
Fill coats are applied by brushing the material into the voids of the surface, sometimes combined with the portland cement binder. This requires good workmanship for successful results. Those fill coats which do not contain latex require application to a moist surface and moist curing for hydration of the portland cement constituent. The fillers containing latex do not require moist curing because the latex retards evaporation of moisture thereby making it available for hydration of the cement binder.
Portland Cement Paints
These paints are sold in powdered form in a variety of colors and are mixed with water just before use. They are produced in standard and heavy duty types. The standard type contains a minimum of 65 percent portland cement by weight and is suitable for general use. The heavy duty type contains 80 percent portland cement and is used where there is excessive and continuous contact with moisture, such as in swimming pools. Each type is available with a silicious sand additive for use as a filler on porous surfaces. Portland cement paints set by hydration of the cement which bonds to the masonry surface. They are applied to moist surfaces by stiff brush and dampened by fine water spray for 48 to 72 hours until the cement cures. Portland cement paints contain little organic material and are not subject to attack from alkali found in new concrete. They have a long history of success in waterproofing masonry when properly applied and cured.
Latex Paints
Latex paints, inherently resistant to alkali, are made of water emulsions of resinous materials. They dry throughout as soon as the water of emulsion has evaporated, usually within 1½ hours. Styrene-butadiene is one of the original synthetic chemical coatings and is still in use. Other latex coatings such as polyvinyl acetate and acrylic resin are presently in greater demand, and are also available as clear coatings for colorless applications. All latex paints are available as opaque coatings. Latex paints may be applied to damp or dry surfaces and require no curing. Although acrylic latex is somewhat higher in cost than the other latex waterproofing materials, it has demonstrated superior resistance to penetration by rain and shown greater overall durability.
Oil Base Paints
Oil base paints are manufactured from natural oil resins or synthetic alkyd resins. Similar to conventional house paints, the oil base paints designed for use on masonry are usually reinforced by certain resins to improve their resistance to alkali. They may be applied by brush, roller, or spray. A dry masonry surface is required at the time of application and, the effective alkalinity of the surface must be reduced through aging the masonry or application of surface pretreatments. Oil base paints which are subjected to dampness from within the masonry may fail from blistering and peeling.
Chlorinated Rubber Base Paints
These paints are composed of chlorinated natural rubber which is blended with pigments and resins. Often termed rubber-base paints, they may be applied to dry or slightly damp surfaces. The heavy consistency of these paints contributes toward filling the voids of porous surfaces and is conducive to application by roller. They possess good resistance to alkali and are highly impermeable to vapor but show a tendency to lose adhesion, especially near a break in the film.
Epoxy Coatings
These coatings are based on epoxy or urethane resins to which a catalyst is added just before application. The epoxies are highly resistant to alkali and form an impervious film. Outdoor exposure of epoxy paints results in chalking which must be removed by washing with soap and water to restore the original appearance. The high cost of the material and difficulty experienced in application have limited the use of epoxies to specialized requirements. They are not recommended for general use on concrete masonry.
Silicone Based Coatings
Silicone is a colorless resinous material produced by a synthetic process from silicon-dioxide. When applied to masonry surfaces, silicone-based coatings do not cause a change in color or texture. Without actually sealing openings, silicones retard water absorption by changing the contact angle between water and the walls of capillary pores in the masonry. Silicones do not bridge large openings; therefore, fill coats are desirable on coarse textured masonry. Application of silicone-based coatings is commonly accomplished by flooding the surface with a low pressure spray head.
Bituminous Coatings
These coatings are produced from coal-tar or asphalt and are furnished in solid form to be melted for hot application. They are also available in liquid form, either diluted in solvent or emulsified with water, for application at normal temperature. Hot application of bituminous coatings may be made alone or in combination with felt or other reinforcing fabric to form a built-up membrane. Where considerable hydrostatic pressure is exerted upon the coating, the built-up membrane has the distinct advantage of maintaining continuity of waterproofing over possible imperfections in the wall. The low cost and excellent resistance to penetration of water favor the use of bituminous coatings where appearance is not important, such as below grade portion of basement walls.
Selection of Coatings
Figure 1. illustrates the direction in which moisture moves through concrete masonry walls above and below grade, and the type of permeability desirable in protective coatings applied to interior and exterior surfaces. For above grade masonry walls, the interior surface should be an impermeable (non-breathing) barrier to reduce passage of moisture from inside the building to the interior of the wall itself. However, some flow due to imperfections will occur, and moisture will also tend to enter the wall through leaks in the exterior coating, parapet, sills, flashing etc. The exterior surface should, therefore, be permeable enough to permit transpiration of entrapped moisture to the outside atmosphere, but at the same time, the exterior surface should be resistant to inward passage of water. If the exterior coating is impermeable, blistering will occur and freezing and expansion of entrapped moisture will cause crazing and surface disintegration of the masonry.
The reverse situation exists in masonry walls below grade. Vapor flows from the exterior buried surface to the interior face due to imperfections in exterior impermeable membranes. Consequently, the coating on the interior surface must be somewhat permeable to prevent blistering and resultant flaking or peeling. Significant reduction in the flow of vapor through masonry walls below grade can be achieved through application of waterproof coatings on the interior surface, but repairs to flow of water under pressure cannot be accomplished from the inside by this method.
The problems associated with leakage through masonry walls below grade can almost invariably be traced to a causative factor other than the masonry itself and warrant special consideration. A foundation wall properly designed with adequate footings to avoid cracking from differential settlement, and constructed in accordance with accepted standards of good workmanship will give excellent, lasting service. It cannot be overemphasized that the time to waterproof basement walls is during construction, before backfilling has begun. For residential-type construction in wet soil, the earth side of