Mat-faced gypsum board

Details Mat-faced gypsum board Mat-faced gypsum board

2001-04-19

2004-08-03

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Weight per unit area specified

C428S220000, C428S703000, C442S283000, C442S284000, C442S285000, C442S288000, C442S290000

Reexamination Certificate

active

06770354

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an improved fibrous mat-faced gypsum board, for example, gypsum board faced with glass fiber mat. More particularly, the present invention relates to a gypsum board faced with a coated glass fiber mat. The coating comprises a dried aqueous mixture of a mineral pigment; a first binder comprised of a polymer latex adhesive; and, a second binder comprised of an inorganic adhesive.
The present invention is particularly advantageous for use in any application in which the fibrous mat-faced gypsum board is expected to be exposed to a high humidity or high moisture environment during installation or use, such as in shaft walls, stairwells, area separation walls, return air installations and as a tile backer in bathroom applications. Still other applications and uses will become apparent from the detailed description of the invention, which appears hereinafter.
BACKGROUND OF THE INVENTION
Panels of gypsum wallboard which comprise a core of set gypsum sandwiched between two sheets of facing paper have long been used as structural members in the fabrication of buildings where the panels are used to form the partitions or walls of rooms, elevator shafts, stairwells, ceilings and the like. A specialty application for the use of panels of gypsum wallboard, as well as other types of building panels, is the use thereof in bathrooms—typically a place of high humidity and residual water because of the flow of water from the use of showers, bathtubs, and sinks. Gypsum wallboards suitable for use in these applications share a common requirement; that is a resistance or tolerance to high humidity and high moisture environments, often for prolonged periods.
A usual construction of bathroom walls includes a multi-ply structure of ceramic tile adhered to an underlying base member, for example, a panel of wallboard comprising gypsum or other material as will be described below. Such a panel is referred to in the industry as a “tile backing board,” which for convenience is referred to herein as “tile backer”. In usual fashion, sheets of tile backer (for example, 4′×8′×½″) are fastened by rust-resistant nails or screws to studs. Blocks of ceramic tiles (for example, 4″×4″) are adhered to the sheets of tile backer by water-resistant adhesive which is referred to in the industry as “mastic” or by a Portland cement-based adhesive which is referred to commonly as “thin set mortar”. Thereafter, spaces between the tiles and between the tiles and other adjoining surfaces, for example, the lip of a bathtub or sink, are filled with a water-resistant material which is referred to in the industry as “grouting”.
It should be appreciated that a primary goal in constructing a bathroom that includes one or more of a bathtub, shower and sink is to make the contiguous and adjacent walls water-tight utilizing materials that resist being degraded by water, including hot water. Tiles made from ceramics are such materials and are basically inert to both the hot and cold water with which the tiles come into direct contact.
It is important also that the tile backer to which the tiles are adhered be water-resistant. Theoretically, it would seem that the water-resistant properties of the tile backer should be inconsequential because the backer is shielded from shower, bath and sink water by water-resistant tiles, grouting and mastic. However, experience has shown this is not the case and that moisture can and does in fact seep through the plies of material which overlie the tile backer. This can happen in various ways.
One way has to do with the fact that grouting is not water-impervious and over time permits the seepage of moisture, a situation which is aggravated upon the formation of cracks, including hairline cracks, in the grouting. Eventually, the moisture which penetrates through the grouting finds its way through the mastic and comes into contact with the paper facing of the wallboard. Such paper facing is typically a multi-ply paper, which upon contact with moisture tends to degrade by delaminating or otherwise deteriorating. For example, the paper facing is subject to biological degradation from mold and mildew. The paper can actually rot away. Furthermore, as the moisture comes into contact with the underlying set gypsum core, it tends to dissolve the set gypsum and also the core adhesive, which bonds the core and paper facing together. Such adhesive is typically a starch material. The development of these conditions can lead to tiles coming loose from the underlying deteriorated paper-faced gypsum wallboard. This undesirable situation is exacerbated when hot water comes into contact with the paper-faced wallboard.
Another type of moisture condition which leads to the loosening or falling off of tiles from their underlying support substrate is associated with those segments of the multi-ply wall structure which include a joint formed from an edge portion of the wallboard. An example is the joint formed by the edge of a wallboard panel and the lip of a bathtub. Another example is the joint formed by two contiguous wallboard panels. As moisture penetrates through the multi-ply structure and reaches such a joint, it tends to wet significant portions of the paper facing and core by virtue of its spreading through capillary action. This can lead to delamination of the paper facing and/or dissolution of the core and/or the paper/core adhesive. As this occurs, tiles can come loose and fall off.
The present invention relates to the provision of an improved gypsum-based structural panel of the type which can be used effectively as a tile backer and in other applications such as in the return air installations, shaft walls and area separator walls in commercial buildings where water and humid conditions are commonly encountered. Still other applications where moisture and humid conditions are likely to present difficulties with paper-faced gypsum board either during the installation or the use of the board will be apparent to those skilled in the art.
In efforts to mitigate or overcome problems associated with the use of paper-faced gypsum wallboard in applications where moisture exposure is expected to occur, the prior art has approached the problem in various ways over the years.
One approach to the problem has been to treat the paper comprising the facing of the wallboard with a water-resistant material sometimes referred to as a water-repellant. Polyethylene emulsion is an example of a material that is used to treat paper facing to impart water-resistant characteristics. Such treatment is designed to deter delamination of the multi-ply paper facing by reducing the tendency of the paper to absorb water which is a chief cause of delamination and to deter water from penetrating through the paper to the gypsum and destroying the bond between the paper-facing and gypsum core.
Another approach to the problem has involved incorporating into the formulation from which the gypsum core is made a material that functions to impart improved water-resistant properties to the set gypsum core itself. Such an additive tends to reduce the water-absorbing tendency of the core and decrease the solubility characteristics of the set gypsum. Wax-asphalt emulsions and wax emulsions are examples of such an additive.
Although improvements have been realized by the provision of gypsum wallboard prepared in accordance with these teachings, further improvements are still possible. Over a period of time, experience shows that tiles come loose from tile backer of boards having treated-paper facers, as the paper facing delaminates and the gypsum core erodes through the degrading action of moisture. The problem is particularly aggravated by warm water acting upon a gypsum core that includes either a wax emulsion or a wax-asphalt emulsion, commonly used, water-resistant core additives. While cores containing such materials have quite good water-resistant characteristics in the presence of water at room temperature, such characteristics start to fall of

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