EPDM membranes, which are cured sheets of ethylene-propylene-diene copolymer rubber, are often used in the construction industry to cover flat or low-sloped roofs. During manufacture of the EPDM membranes, uncured sheets, also referred to as green membranes, are rolled and placed into a curing oven to effect vulcanization of the rubber in the presence of a cure system. In order to prevent the roll of green membrane from sticking to itself (“blocking”), and ultimately curing to itself, the membrane is treated with a dusting agent prior to being rolled and cured. Industry standards include the use of talc and mica for dusting, although other materials have been used such as, for example, cellulosic materials.
These membranes, which may also be referred to as panels, are typically delivered to a construction site in a bundled roll, transferred to the roof, and then unrolled and positioned. The sheets are then affixed to the building structure by employing varying techniques such as mechanical fastening, ballasting, and/or adhesively adhering the membrane to the roof. The roof substrate to which the membrane is secured may be one of a variety of materials depending on the installation site and structural concerns. For example, the surface may be a concrete, metal, or wood deck, it may include insulation or recover board, and/or it may include an existing membrane.
In addition to securing the membrane to the roof—which mode of attachment primarily seeks to prevent wind uplift—the individual membrane panels, together with flashing and other accessories, are positioned and adjoined to achieve a waterproof barrier on the roof. Typically, the edges of adjoining panels are overlapped, and these overlapping portions are adjoined to one another through a number of methods depending upon the membrane materials and exterior conditions. One approach involves providing adhesives or adhesive tapes between the overlapping portions, thereby creating a water resistant seal.
Thus, there are two modes of membrane attachment that are used in conjunction to create a water impermeable roofing membrane assembly. The first seeks to anchor the membrane to the roof, while the second seeks to create a water impervious barrier by attaching individual adjacent membrane panels to each other or to flashing. Inasmuch as these modes of membrane attachment seek entirely different goals, the mechanisms by which they operate are likewise highly distinct.
With respect to the former mode of attachment, which involves securing of the membrane to the roof, the use of adhesives allow for the formation of a fully-adhered roofing system. In other words, a majority, if not all, of the membrane panel is secured to the roof substrate, as opposed to mechanical attachment methods which can only achieve direct attachment in those locations where a mechanical fastener actually affixes the membrane.
When adhesively securing a membrane to a roof, such as in the formation of a fully-adhered system, there are two common methods employed. The first is known as contact bonding whereby technicians coat both the membrane and the substrate with an adhesive, and then mate the membrane to the substrate while the adhesive is only partially set. Because the volatile components (e.g. solvent) of the adhesives are flashed off prior to mating, good early (green) bond strength is developed. The contact bonding method employs adhesives that may include volatile organic compounds (i.e. solvent-based adhesives). Water-based adhesives are used for contact bonding as well, but the water does not flash off quickly and therefore the use of water-based adhesives for contact bonding may be fraught with problems.
The other method of adhesively securing a membrane to a roof is known as wet lamination, whereby technicians coat the substrate with an adhesive and then mate the membrane with the substrate while the adhesive is still wet. This method can therefore advantageously employ water-based adhesives due to the fact that the mating step can occur immediately after application of the solvent, which significantly reduces installation time. But, wet lamination can only be used when the substrate to which the membrane is being adhered is porous (e.g. wood, plywood, or OSB board), which allows the water to dissipate through the substrate. The use of this technique to secure a membrane to a non-porous substrate, such as an existing membrane, is not a viable option because water from the water-based adhesive is trapped between the non-porous substrate and the membrane (which is also non-porous).
Nonetheless, wet lamination is a preferred method for a variety of reasons, including that the water-borne adhesive need only be applied to one surface, the method does not require drying time, the method is less sensitive to heat and sun conditions during application, less labor intensive, uses less material, and it uses environmentally-friendly water-borne adhesives.
Therefore, there is a need for an improved method of adhering roofing membranes to a roof substrate that facilitates adhesion to non-porous surfaces using the wet lamination technique.