Patent Application
20050126109
The present invention pertains to the prevention of galvanic corrosion of metal fasteners used in wood assemblies, and more particularly to methods for separating zinc-coated metal from copper ions leached from pretreated wood deck components.
Among the wood preservatives used in the last two decades for making outdoor wood constructions such as decks, chromated copper arsenate (CCA) has been the most popular. However, as arsenic is a known carcinogen, the U.S. Environmental Protection Agency (EPA) and wood preservative industry have reached agreement, effective Dec. 31, 2003, to employ less toxic alternatives.
Two such alternatives, Alkaline Copper Quat (ACQ) and Copper Azole (CA), have been approved by the American Wood Preserver's Association for outdoor use. However, the present inventors believe these new treatments can create a serious problem in that they are more likely than CCA to accelerate the corrosion of metal fasteners that are typically are used in assembling wood decks. While all of these preservatives contain copper, which can leach out of the wood and deposit as an oxide on the metal fastener, thereby creating a galvanic potential and thus oxidation and corrosion, the inventors realize that CCA contains an anodic inhibitor (chromate) and a cathodic inhibitor (arsenate) to slow down corrosion, whereas ACQ and CA do not.
The present inventors believe that without such inhibitors ACQ and CA will facilitate corrosion in metal fasteners as well as in metal “joist hangers” and other metal connector devices used in deck assemblies and other outdoor wood constructions. Certain forms of ACQ, moreover, contain chlorides that exacerabate the corrosion problem. Failure of joist hangers could lead to injury or death, and must be avoided. Although decay resistant woods (e.g., redwood, cedar), woodfiber/plastic composites, and/or stainless steel fasteners and devices can be substituted, these are all far more expensive than using common stock lumber, fasteners, and joist hangers.
A less expensive method for assembling outdoor wood structures is needed.
In resolving the aforementioned problem, the present invention provides an inexpensive and convenient method for resisting corrosion of metal connection devices (e.g., joist hangers) and metal fasteners used in assembling wood decks and other outdoor wood assembly constructions.
Exemplary methods of the present invention comprise separating, from metal connector devices, the wood components connected by the metal devices. This anomalous condition is actually deemed beneficial in the circumstances wherein at least one, or both, of the wood components is pretreated with a preservative such as alkaline copper quat (ACQ), ammoniacal copper quat (ACQ-B), copper azole (CA), or mixture thereof. A membrane barrier, comprising a carrier support layer and a pressure-sensitive waterproofing adhesive layer, is therefore used as a separator, to prevent copper from emanating from the pretreated wood under wet conditions and contacting the metal connector device (e.g., joist hanger) used for assembling the wood structure. Preferably, the membrane barrier operates to seal around metal fasteners used for securing the metal connector device to the wood components, so as to prevent water from migrating from the pretreated wood through the penetration to the metal device and metal fastener heads.
The present invention is particularly useful for minimizing galvanic corrosion of zinc-coated metal joist hangers and fasteners employed in assembling decks made from wood pretreated with ACQ, ACQ-B, and/or CA. In preferred methods, the ends of a plurality of wood joists are capped with the membrane barriers, and these ends are connected by metal connector device to the surface of a rim joists which, in turn, are covered at the point of contact with membrane barrier. Metal connector devices include metal joist hangers, plate, or braces, which are fastened to the wood by metal fasteners driven through the membrane barriers. In this manner, an entire pretreated wood construction can be assembled. The present invention therefore also pertains to wood construction assemblies provided by the above-described method.
Further advantages and features of the present invention are described in further detail hereinafter.
The advantages and features of the invention can be more readily comprehended when the following detailed description is viewed in conjunction with the accompanying drawings, wherein
As shown in
In the present invention, however, the inventors believe it is equally important to employ a membrane barrier to separate the metal connector devices (e.g., joist hangers, plates, braces, typically made of galvanized steel) used for connecting wood components that have been treated with preservatives, as described herein and below.
As previously summarized above, the present invention is prompted by a recent change in the nature of wood preservatives used. Under wet conditions, the new preservatives can facilitate corrosion in the metal connection devices and metal fasteners, and particularly in zinc-coated connector devices such as joist hangers.
Preferred membrane barriers suitable for use in the invention comprise a carrier support layer, and, contiguously attached thereto, a preformed pressure-sensitive waterproofing adhesive layer. The carrier support layer is preferably plastic film or metal foil, although cloth and paper may, alternatively, be employed. Most preferred is a continuous film of cross-laminated polyethylene. The waterproofing adhesive layer is made preferably of rubberized asphalt, natural or synthetic rubber (e.g., butyl rubber, butyl rubber with EPDM), or combinations thereof. In cold weather applications, it may be advisable to employ a primer to facilitate adhesion of the pressure-sensitive adhesive to the wood surface. Thicknesses of membrane barriers can be between 10-100 mils or more, with preferred thicknesses from 20-40 mils. The thickness of the carrier support film may be 2-10 mils in thickness, while the preformed adhesive layer may be 10-75 mils, and more preferably 15-45 mils thickness. A suitable membrane barrier is commercially available from Grace Construction Products, Cambridge, Mass., under the tradename VYCOR®.
Exemplary wood assemblies of the present invention involve wood components, such as joists or beams, sheets, or other shaped components that are pretreated with one of the following preservatives, which are terms of art known in the wood preservatives trade: Alkaline Copper Quat (ACQ), which may also be referred to as ACQ-C (Type C), which contains chloride, or ACQ-D (Type D), which does not contain chloride; Ammoniacal Copper Quat, which may sometimes otherwise be referred to as ACQ-B (Type B); and Copper Azole (CA), which may sometimes otherwise be referred to as CA-A (Type A) or CA-B (Type B). The term “pretreated” as used herein may refer either to the fact that the wood has been coating or impregnating with any of the foregoing preservatives. Pretreated wood used in the present invention will typically comprise pine, and, more specifically, southern pine lumber.
As illustrated in
The most prevalent form of wood components envisioned for use in the invention are beams, or joists, having elongated, generally rectangular shapes.
In further exemplary methods and assemblies of the invention, both of the wood components 10 and 12 are partially covered by membrane barrier material at the locations where they are intended to make abutting contact with each other. The reason for this is to prevent copper-carrying water or moisture from the wood to flow onto the surfaces of the metal connector device. Accordingly, it is preferred to place membrane barrier on both surfaces of the wood components where they abut, since this locating would be close to the actual contact surfaces to which the metal connector devices would be attached. The second component 12 could be a wood rim joist (otherwise called a “ledger board”) to which a plurality of wood joists are connected using a number of metal connecting devices similar to the one designated at 20 in
Thus, while it is nevertheless advisable to cover the top of the joist 10 and rim joist 12 with membrane barrier material 14/16, as would be suggested by the prior art flashing method illustrated in
The present invention will be useful not only for attaching wood joists to rim joists in wood decks, but also for connecting structural wood components together in most outdoor wood constructions, wherein the metal connector devices are preferably sheltered from the sunlight (such that the pressure-sensitive adhesive on the membrane barrier is not quickly degraded). Wood assemblies such as barns, sheds, or mail box supporting structures can also be constructed using the methods described herein.
Accordingly, in further exemplary methods and wood assemblies of the present invention, two or more wood components pretreated with ACQ, ACQ-B, or CA may be connected together using metal connector devices having a variety of shapes, such as plates or brackets (flat or bent), wherein the wood surfaces thereof for mounting the metal connector devices are protected by membrane barrier material, which operates to separate the metal connector devices from the wood components that they connect (and more importantly from the copper emanating from the wood under wet conditions), and, concomitantly, to seal around metal fasteners used for attaching the metal connector devices to wood.
It is preferably that the wood surfaces directly in abutting contact be covered as well, and not merely the wood surfaces contacted by the metal connector devices (e.g., joist hangers), since the such abutting wood surfaces could also provide a source of copper (from ACQ, ACQ-B, or CA). Hence, it is wise to “cap” the ends 14 of elongate components such as the joist 10 as shown in
In the case of horizontal wood joists, it is preferred to cap the opposing ends (including the very end surface and surrounding adjacent bottom and sides surfaces of the joist) to an extent commensurate with coverage required by the joist hanger or other metal connector device requiring physical contact with the wood component.
Generally, preferred methods of the invention comprise applying a membrane barrier to abutting surfaces of first and second wood components at areas whereby said first and second wood components abut or otherwise come into contact with each other, as well as to surfaces of said wood components immediately adjacent to the location where a metal connector device is used for fastening the first and second wood components together. For example, a membrane barrier can be mounted beneath a flat metal plate, corner bracket, L-bracket, such as may be used for connecting two or more wood pieces together.
In still further exemplary methods of the invention, a plurality of pretreated wood joists are capped at their opposing ends with membrane barrier, and connected to another pretreated wood structure, such as a wood rim joist or ledger board, whereby the other wood structure is also covered with membrane barrier at the point at which the pretreated joists will be connected to the pretreated structure, and metal connector devices used for fastening the joists and structure together are separated to prevent galvanic corrosion of the metal connector device due to ACQ, ACQ-B, or CA emanating from the wood.
In other exemplary embodiments, the membrane barriers may optionally contain a skid-resistant surface (e.g., polymer coating, sand granules) on the backside of the carrier support sheet opposite the adhesive layer, in order to resist skidding of foot traffic, as in the case where the tape is also used for protecting the top of joists or rim joists, or otherwise where the wood surface may be positioned to sustain foot traffic. Skid resistant coatings, as may be generally known for use on waterproofing membranes and roof underlayments, may be employed in this present context.
The present invention also provides wood construction assemblies, such as wood decks, made by the methods described above. A preferred embodiment comprises a pretreated wood deck, such as may be found on an outdoor porch or wood bridge (preferably covered wood bridge), wherein horizontal wood joists are capped by and the upper joist surfaces thereof are covered by a membrane barrier, as described above, said joists being attached to wood rim joists or ledger board at abutting regios which are covered by a membrane barrier using metal connector devices fastened to said joists using metal fasteners driven through and sealed by said membrane barrier. Wood planks are attached to said horizontal wood joists using nails or screws that are driven through the membrane barriers covering the upper surface of said horizontal wood joists. Preferably, the membrane barrier has a skid-resistant coating (preferably elastomeric coating) on the side of the carrier support sheet opposite the side on which the waterproofing adhesive layer is located, such that construction workers can walk on the exposed horizontal joists during installation of the planking.
In particularly preferred methods and construction assemblies of the invention, the membrane barrier is non-water-absorptive. For example, it is known that certain membrane barriers may, in addition to a plastic sheet carrier support and waterproofing adhesive, employ a mat (e.g., fiberglass) that can operate to absorb water. Thus, preferred membrane barriers of the invention will not contain water-absorptive components such as mats or nonwoven fabric layers.
In still further exemplary methods and embodiments, one or more wood components may be pretreated alternatively with a borate (e.g., sodium borate).
The foregoing exemplary and preferred embodiments are provided for illustrative purposes only, and not intended to limit the scope of the invention.
