Modern techniques for constructing building walls include, for example, the two-by-four (2×4) framed construction, comprising wood or metal (such as, steel) members. These 2×4s are oriented vertically and connected at the top and bottom to similar members that are horizontally oriented. This structure is referred to in the relevant art as a “framed” wall. A sheet of building wall substrate or exterior sheathing wallboard, such as plywood sheathing, specially formulated gypsum wallboards, cement panels, or fiber cement panels are affixed to building frame.
A water-resistive barrier is then typically applied to the exterior of the sheathing wallboard, with an external wall cladding or finish then being applied directly over the water-resistive barrier. Many materials may be used for the external wall finish such as brick, stucco, vinyl or aluminum siding, and/or wood. For example, stucco exterior finishes make up one of the most common ways of finishing exteriors of both residences and commercial buildings. Stucco finishes have limitations including, porosity, rigidity, freeze/thaw fractures, fungal and mildew formation, cracking, and compromised weatherability if not applied properly. However, because modern exterior finishes are watertight, any water that remains trapped behind these finishes does not readily evaporate. The trapped water behind the exterior finish can then soak into the substrata, for example, the sheathing wallboard and framing of the building. The water that soaks into the substrata and framing often causes severe damage to the building without any signs of damage appearing on the exterior of the building. These problems can exist regardless of the age of the building or the quality of construction.
The exterior sheathing wallboards such as gypsum (or other) wall-boards used as structures, are joined at edges by joint compounds. During construction, these exterior sheathing wallboards are exposed to outside environment, which, compared to the interior environment of a building is rather severe. The exterior sheathing wallboards are exposed to UV, rain, wind, heat, cold, and other physically abrasive impactors such as debris, insects and birds, particularly during construction work. Thus, these boards are specially formulated to have weatherability and particularly water resistance of 100 g/m2 or lower 2-hour water permeance or Cobb value. Just like interior drywall panels, exterior sheathing wallboard panels, when installed, have seams or joints between each panel that must be filled so that a smooth exterior finish may be applied. The joints between these exterior wall-boards or sheathing, therefore, become the weak link from where moisture can penetrate through the walls of the building and into the interior. Currently, the joint compound (or the water resistive barrier) used to seal the joints between the sheathing and to provide water resistance include a silyl-terminated-polyether (STPE) flashing membrane system. The Cobb value of such STPE systems is around 2 g/m2. Stated another way, the joint compound or the sealant that is currently used is about thirty times more water resistant than the gypsum wall-boards having the much larger exposed area. The STPE based systems are not water based and therefore have inherent issues relating to dealing with organic chemical solvents. Also, these are very expensive systems.
For the exterior or the interior wallboards, to achieve a smooth, visually appealing surface, the joints between boards, cracks, screw holes, and/or nail holes must be concealed. Conventional wallboard joint compounds for the interior are used to cover and finish gypsum wallboard joints, cornerbead, and screw or nail holes. Joint compounds can be spread over mesh or tape used to connect wallboards. It may also be used to patch and texture interior walls. The intrusion of water through wall spaces, either through prolonged direct contact or via high humidity, has a debilitating effect (mold and structural damage) on standard wall systems. The result of water seepage through joint compound to the studs on the other side of the wall ultimately has devastating structural and microbial implications for the wall system, first by absorption of the seeped water into the wood studs followed by their swelling and deformation (leading to expensive structural problems) and then, the creation of a fertile ground for rapid mold growth.
Some performance requirements of exterior sheathing wallboards include (1) long-term weather-resistance; (2) mold resistance; and (3) water resistance. These performance characteristics are quite stringent, and it is to be expected that whichever material that is to be used to cover the joints between these sheathing boards (as well as the nail heads) should, at a minimum, display the same performance characteristics as that of the corresponding sheathing wallboards. It is problematic achieving all of these characteristics, especially water and weather resistance with a water-based system. This is because a water based system would have a higher propensity to degrade or be washed away with time. It is for this reason that the joint fillers for exterior sheathing boards have largely been non-water based materials such as silyl-terminated polyethers. Where water based formulations have been used, they have had to be very high in latex content and correspondingly low in water content. Formulations that are high in organic polymer content (such as STPE and water based acrylic latexes) invariably come with handling difficulties such as poor washability and undesirable odors. This invention addresses the above problems and relates to an exterior joint compound that has a significantly lower acrylic latex content, yet displays exceptional water, weather, and mold resistance. This inventive joint compound contains a specially formulated wax emulsion designed to impart exceptional water repellency to coatings formulations. Particularly, the invention relates to exterior joint compounds that are water-based but with water repellant and anti-microbial character. Because the exterior of a building especially during construction is exposed to sever weather conditions such as rain and moisture, it is counterintuitive to envision using a water-based system that can handle the harshness of the exterior environment especially when such joints serve as the weak link for moisture entry. Wax emulsions have been used in composite wallboard (e.g., gypsum wallboard) for many years for the interior in the building industry. For example, wax emulsions sold under the trade name AQUALITE® by Henry Company, and several wax emulsion formulations are disclosed in the prior art, such as U.S. Pat. No. 5,437,722. However, wax emulsions have not been used in exterior joint compounds. The inventors of this invention have arrived at a water based formulation that includes wax-based emulsion systems as one component to be used a joint compound between the exterior sheathing wallboard panels.