1. Field of the Invention
 This invention relates generally to a composite structural panel, and more particularly to an asymmetrical concrete backerboard having fiberglass mesh reinforcement on one side, and an impervious reinforcement membrane on the opposite side of the board.
 2. Description of Related Art
 The conventional backerboard is made up of a rectangular panel of solid concrete, the concrete core, having both major surfaces covered with fiberglass. The fiberglass adds strength to the board, and provides only limited resistance to water penetration through the board. Concrete backerboards are used extensively in the construction of interior and exterior floors, walls and ceilings. The concrete backerboard is a superior substrate or underlayment for stucco, ceramic tile, marble, and other tile-like surfaces located in wet areas, such as shower walls and bathtub surrounds, and building exterior walls.
 Typically, the concrete core of the backerboard is a low density, high compressive strength, concrete core. The fiberglass mesh reinforcement layers overlay both major faces of the core, with each of these pervious fiberglass layers themselves covered with a thin layer of Portland cement. Backerboards have textured cementitious surfaces that provide for a high strength bond with mastics and Portland cement mortars that are used to adhere tile to the substrate in wet areas.
 While the conventional backerboard is generally stable and water resistant, it is not an ideal construction panel for use in wet environments due to several inherent limitations. For example, it is generally recommended by backerboard manufactures, and required by most building codes, to use an additional impervious moisture barrier behind the backerboard. Thus, contractors are forced to install the backerboard and separate moisture barrier in the field, at the construction site. Use of a impervious barrier membrane with the backerboard provides protection for the wood or steel structures under or behind the backerboard, and contains the moisture in the wet area. Examples of commonly used moisture barriers are felt paper, Tyvek®, spunbonded olefin and polyethylene.
 An exemplary patent in this field includes U.S. Pat. No. 3,284,980 to Dinkel disclosing a precast panel of cement and aggregate reinforced with a skin membrane of fibrous material. Backerboard manufacturing techniques include a lightweight aggregate core faced on each side or face with a fiberglass mesh material bathed in a slurry of neat cement and pressed against the aggregate core, such that when the neat cement and the aggregate core are cured, there is provided a composite, fiberglass mesh reinforced, cementitious panel. U.S. Reissue Pat. No. Re32,037 to Clear is a method for manufacturing cementitious reinforced panels and illustrates a concrete panel
 It is evident from the prior art that an improved backerboard and method of constructing such an improved backerboard is needed. It can be seen that there is a need for a backerboard having at least one waterproof surface that can be delivered ready-made to the construction site, and a method for producing such a backerboard without resort to a carrier sheet.
 Briefly described, in a preferred form, the present invention is a backerboard having a fiberglass mesh on one side, and an impervious moisture barrier membrane on the other side. Such an asymmetrical backerboard design (the two major surfaces of the core having differing moisture-resistant layers, providing different moisture-resistant properties) incorporates numerous advantages over the conventional backerboard design, including having lower manufacture costs, having a waterproof panel deliverable on-site, and having a simplified manufacturing process by eliminating the use of a carrier sheet or web.
 The present asymmetrical backerboard comprises a low density, high compressive strength concrete core having an upper principal surface and a lower principal surface. The upper principal surface of the core is covered by a fiberglass mesh reinforcement layer, itself covered and bonded to the core by a thin layer of Portland cement. Alternatively, if the core itself comprises a sufficient amount of randomly dispersed fiberglass fibers, the addition of the fiberglass mesh reinforcement layer may not be required. The lower principal surface of the backerboard is covered with a high tensile strength, impervious moisture barrier membrane.
 The present backerboard construction eliminates the prior art necessity of the on-the-construction-site application of a moisture barrier behind the backerboard. It exhibits all of the structural, bonding and workability properties of conventional backerboards, and provides advanced water resistance.
 The present method of constructing the backerboard dispenses with the prior art requirement of a carrier sheet or web. In a preferred embodiment of the invention, the panel is manufactured by the concurrent steps of running a continuous pervious reinforcement web through a web coating bath and then removing excess bath therefrom, and running a continuous impervious reinforcement web through a set of pinch rollers and atop a conveyor belt.
 Core material is dispensed upon the impervious web via a hopper, and the combination of impervious web and core material run through a screed. The core material is then compacted. The bathed pervious web is then fed onto the top of the core material, forming a sandwich of, from bottom to top, impervious web, core material and pervious web. The composite is then cut into panels.
 It is thus an object of the present invention to provide an asymmetrical backerboard and a method for making such a board.
 Further, it is an object of the present invention to provide a construction panel having at least one major surface which is highly resistant to the penetration of water.
 These and other objects, features, and advantages of the present invention will become more apparent upon reading the following specification in conjunction with the accompanying drawing figures.
 The components of the present invention are referenced herein as follows:
NO. COMPONENT NO. COMPONENT 10 Prior Art Backerboard 48 Core Feed Hopper 12 Concrete Core 52 Screed 14 Fiberglass Mesh Reinforcement 54 Compaction Station 16 Layer of Portland Cement 56 Compaction Roll 20 Present Asymmetrical Backerboard 58 Bath 22 Concrete Core 62 Roller Assembly 24 Upper Principal Surface of Core 64 Doctor Assembly 26 Lower Principal Surface of Core 66 Drag Bar 28 Upper Reinforcement Material 72 Step of Feeding 32 Upper Coating 74 Step of Depositing 34 Impervious Membrane 76 Step of Screeding 40 Present Manufacturing Process 78 Step of Compacting 42 Roll of Impervious Membrane 82 Step of Bathing 44 Pinch Roller Assembly 84 Step of Layering 46 Conveyor Belt 86 Step of Cutting
 It should be noted that as used herein the term “pervious” defines a property of a material, that property enabling free water to penetrate through a material, and that the term “impervious” defines a property of a material, that property being highly resistant against enabling free water to penetrate through a material. An impervious material may enable water vapor to penetrate through a material.
 Referring now in detail to the drawing figures, wherein like reference numerals represent like parts throughout the several views,
 As shown in
 The core
 The upper reinforcement material
 The upper coating
 The impervious membrane
 The present manufacturing process
 In a second depositing step
 A third screeding step
 In a fifth bathing step
 The present manufacturing process
 The present invention avoids the carrier sheet problem by providing a backerboard with a cementitious surface on only one side, and a high tensile strength impervious membrane
 While the invention has been disclosed in its preferred forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims.