Dow 790 Silicone Building Sealant

Surface Preparation

Clean all concrete, masonry and stone joints of all contaminants and impurities. Concrete form release agents, water repellents, laitance, surface dirt and rust, all old sealants and other surface treatments and protective coatings are examples of materials that must be removed from the joint surfaces to obtain proper sealant adhesion. Porous substrates should be cleaned where necessary by grinding, saw cutting, blast cleaning (sand or water), mechanical abrading or a combination of these methods as required to provide a sound, clean, dry surface for sealant application.1 Dust, loose particles, etc., should be blown out of joints with oil-free compressed air or be vacuum cleaned. Metal and glass surfaces adjacent to masonry should be cleaned by wiping with an oil-free absorbent cloth saturated with solvent such as xylene or toluene. Do not use alcohols as they inhibit the cure. Follow the solvent manufacturer’s safe handling recommendations and local, state and federal regulations regarding solvent usage.

See Vendor Technical Data Sheet for more info.

Application

Dow Corning 790 Silicone Building Sealant should be applied in a continuous operation. A positive pressure adequate to properly fill and seal the joint width should be employed. Tool or strike Dow Corning 790 Silicone Building Sealant with light pressure to spread the material against the back-up material and the joint surfaces. Do not use soaps, oil or alcohols as tooling aids as they inhibit the cure. Use a tool with a concave profile to keep Dow Corning 790 Silicone Building Sealant within the joint. The sealant can be applied at outdoor temperatures as low as -29°C (-20°F), provided that surfaces are clean, dry and frost-free. As a general rule, condensation or frost should not be a problem above 4.4°C (40°F). It is imperative that uncured silicone sealants are not allowed to contact nonabradable surfaces such as polished granites, metal or glass. Because excess silicone sealant cannot be completely removed with organic or chlorinated solvents, these surfaces must be masked or extreme care taken to prevent any silicone sealant from contacting them during sealant application. Once an uncured sealant contacts the surface, it will leave a film that may change the aesthetic surface characteristics of that substrate. In cases where excess uncured sealant is inadvertently applied to adjacent surfaces, the sealant should be cleaned from nonporous surfaces before curing, using a commercial solvent such as xylene. Follow the solvent manufacturer’s safe handling recommendations and local, state and federal regulations regarding solvent usage.