Water-vapor permeable, air barrier coatings can be formed by applying a liquid coating composition onto a building construction surface. The liquid coating may be spray-applied, brushed, troweled or otherwise coated onto the target substrate, which may include a cementitious surface, such as cement, mortar, masonry, concrete, shotcrete, gypsum, gypsum board and gypsum sheathing, or some other building construction surface, such as wood, plywood, oriented strand board, fiberboard, particle board, rigid insulation, etc.
One product currently available from Henry Company, California, is sold under the trade name AIR-BLOC 07. This liquid product can be troweled or spray applied, then cures to form a coating that resists air leaking while remaining permeable to the passage of water vapor at 7 perms (or 400 ng/Pa.m2.s) per ASTM E96 (Henry Technical Data sheet dated 06/23/06). The composition is a one-component solvent-based, SBR-modified bitumen and includes 1-5 parts Bentonite, 7-13 parts calcium carbonate, 10-30 parts of cellulose fiber, 1-5 parts of ethylene glycol, 10-30 parts of Stoddard solvent (C7-C12 hydrocarbon mixture) and other minor ingredients (Air-Bloc 07 MSDS issued at Nov. 10, 2008). The coating formed by this product is believed to have a hydrophilic domain or channel formed by cellulose fiber and Bentonite allowing passage of water-vapor through the coating. Although this solvent-based product can be applied as low as 10° F., the coating shows low elongation and poor crack bridging properties. Because this product is solvent-based, it has higher VOC (i.e. close to 250 g/L), thus raising environmental concerns and requiring special solvents to clean equipment after use. In addition, solvent-based products are incompatible with damp surfaces and require a fully dry surface prior to applying the product, which can be a challenge in a low temperature environment.
Another product available from Henry Company is sold under the trade name AIR-BLOC 31. This water-based composition can be spray-applied and cures to form a membrane that blocks air and air leakage and purportedly achieves a water vapor permeance of 12.3 perms (or 704 ng/Pa.m2.s) under ASTM E-96 (Henry Technical Data Sheet dated Jul. 15, 2002). This product comprises about 65% total solids, wherein the solids comprise approximately 15 parts calcium carbonate (a typical filler), 35 parts wax (polyethylene or hydrocarbon wax; considered here to act as a filler because it does not form a film), and 50 parts vinyl acetate-acrylate copolymer. It is believed that this product has a microporous structure as a result of high filler level that exceeds the critical pigment volume concentration.
Another type of liquid coating composition for protecting exterior wall and roof surfaces is disclosed in U.S. Pat. No. 4,859,723. This water-based composition includes a water-dispersible polymeric binder (e.g., acrylic polymer) and pigment and filler material, including clay, such that the composition has a pigment volume concentration (PVC) greater than 15. These coating compositions are said to be suitable for application to bituminous built-up roofs, including hot mopped asphalt, and compositions with very low water permeability are considered especially useful. These compositions may include auxiliary agents such as preservatives, buffers, coloring agents, plasticizers, fire retardants, coalescents, disinfectants, and stabilizers (e.g., an anti-freeze material). However, the patentee suggests that the compositions should be applied at ambient temperatures of 50-100° F. (10-38° C.).
An improved water-based, liquid-applied vapor permeable membrane composition is disclosed in WO 2006/076186 and is sold under the tradename PERM-A-BARRIER® VP (W.R. Grace & Co.-Conn.). This membrane composition includes a water soluble polymer (e.g. PVOH), a hydrophobic acrylic polymer and a filler (and other minor components) to provide a water-vapor permeable air barrier membrane on a construction surface. The membrane has good flexibility and crack-bridging characteristics. As a water-based system, it is environmentally friendly and compatible with damp surfaces. However, it can not be used below freezing temperatures.
It is generally difficult to apply a liquid coating at low temperatures because the viscosity of the material increases as ambient temperatures decrease and the curing rate of the membrane slows down, potentially reducing the quality of the membrane produced. In addition, a water-based product cannot be applied below freezing temperatures because it will freeze. Freezing will also cause deterioration of coating properties.
It would be advantageous to provide a water-based, liquid-applied vapor permeable membrane composition that may be applied at low temperatures, particularly at temperatures below freezing (e.g., temperatures in the range of −10° C. to 0° C.), and that will dry to form a membrane film at such low temperatures.