Kossuth, Donald A. (Tonawanda, NY)
Shull, John D. (Tonawanda, NY)

04/592358

01/09/1973

11/07/1966

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National Gypsum Company (Buffalo, NY)

52/416

52/447, 52/288.100, 52/540

E04B2/74; E04F13/04; E04F13/18; E04B2/72; E04F13/02; E04B2/10; B32B1/02

52/416-418,540,447,746,287,274-276,287 161/43,44,86,251,88,89,43,44 156/71,304 287/2.92J

2988134	Continuous butt jointing of thermoplastics	June 1961	Nissel
3149693	Acoustical surfaces	September 1964	Keller et al.
3180058	Joint structure for plasterboard	April 1965	Tillisch et al.
3350257	Plastic-covered gypsum wallboard	October 1967	Hourigan et al.

Abbott, Frank L.

Ridgill Jr., James L.

What is claimed is

1. A predecorated wallboard for forming joints having practically invisible seams in simulated monolithic predecorated wall construction and comprising a core panel of elongated generally rectangular shape and having on its front side a substantially flat central surface having opposite marginal portions and arranged between recessed marginal surfaces extending from said opposite marginal portions of said flat central surface to opposite longitudinal edges of said core panel, said recessed marginal surfaces having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet forming a decorative plastic front wall surface, said sheet being laminated only to said flat central surface, but not to said marginal portions thereof nor to said recessed marginal surfaces, throughout the length of said front side and including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto and terminating substantially flush with one longitudinal edge of said core panel and another flap extending over the opposite marginal portion and the opposite recessed marginal surface adjacent thereto around the opposite longitudinal edge onto the rear side of said core panel and being temporarily secured to but removable from said rear side to overlap with an adjacent flap corresponding to said one flap.

2. The predecorated wallboard of claim 1 wherein said core panel includes a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paper facing layer, said recessed marginal surfaces taper edgewise toward the rear side of said core panel and have a minimum width to depth ratio of about 3.75/1, and said decorative sheet includes an inner cloth backing layer laminated to said paper facing layer and an outer polyvinyl chloride layer forming a decorative front wall surface.

3. In simulated monolithic predecorated wall construction, a substantially flat joint including two adjacent predecorated wall boards, each comprising a core panel having on its front side a substantially flat surface having a marginal portion and a recessed marginal surface extending from said marginal portion of said flat surface to an edge, said recessed marginal surface having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet laminated only to said flat surface, but not to said marginal portion nor to said recessed marginal surface, one of said decorative sheets on one of said core panels including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto at least adjacent one of said edges prior to completion of said joint, the other of said decorative sheets on the other of said core panels including another flap extending over the other of said marginal portions and the other of said recessed marginal surfaces adjacent thereto at least beyond the other of said edges to overlap with said one flap prior to completion of said joint, said core panels being arranged with said front sides substantially flush, said recessed marginal surfaces adjacent, said edges in substantially abutting relationship and said flaps adjacent, a hardened joint cement layer filling the space between said recessed marginal surfaces and flaps to substantially the level of said flat surfaces, and upon completion of said joint, said flaps being adhered to and extending over said marginal portions and said cement layer into substantially edge abutting and flush relationship to form a practically invisible seam produced by folding said flaps back out of the way to expose said marginal portions and recessed marginal surfaces prior to said filling of said space with said cement layer, adhering said flaps to said marginal portions, cement layer and each other with said flaps overlapping, cutting through the overlapping portions of said flaps over said cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap and readhering the remainder of the overlying flap to the underlying one of said marginal portions and said cement layer.

4. The joint of claim 3 wherein each of said core panels includes a set cementitious core enclosed on opposite sides and each of said abutting edges with a fibrous facing layer, said marginal surfaces taper edgewise toward the rear sides of said core panels and have a minimum width to depth ratio of about 3.75/1, and each of said decorative sheets includes an inner fibrous backing layer laminated to said fibrous facing layer and an outer plastic layer forming a decorative front wall surface.

5. The joint of claim 3 wherein each of said core panels is of elongated, generally rectangular shape and has on its front side a substantially flat central surface having opposite marginal portions and arranged between recessed marginal surfaces extending from said opposite marginal portions of said flat central surface to opposite edges of said core panel, said recessed marginal surfaces having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet laminated only to said flat central surface, but not to said marginal portions thereof nor to said recessed marginal surfaces, throughout the length of said front side and including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto and terminating substantially flush with one longitudinal edge of said core panel prior to completion of said joint and another flap extending over the opposite marginal portion and the opposite recessed marginal surface adjacent thereto at least beyond the opposite longitudinal edge of said core panel to overlap with an adjacent flap corresponding to said one flap prior to completion of said joint, said core panels being arranged with said front sides substantially flush, said one recessed marginal surface on one of said core panels adjacent said opposite recessed marginal surface on the other of said core panels, said one longitudinal edge of said one core panel in substantially abutting relationship with said opposite longitudinal edge of said other core panel and said one flap on said one core panel adjacent said other flap on said other core panel, a hardened joint cement layer filling the space between said adjacent recessed marginal surfaces and flaps to substantially the level of said flat central surfaces, and upon completion of said joint, said one adjacent flap being adhered to and extending over said one marginal portion and said cement layer but terminating short of said one abutting edge and said other adjacent flap being adhered to and extending over said opposite marginal portion and said cement layer beyond said other abutting edge into substantially edge abutting and flush relationship with said one adjacent flap to form a practically invisible seam produced by folding said flaps back out of the way to expose said marginal portions and recessed marginal surfaces prior to said filling of said space with said cement layer, adhering said adjacent flaps to said marginal portions, cement layer and each other with said adjacent flaps overlapping, cutting through the overlapping portions of said adjacent flaps over said cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap and readhering the remainder of the overlying flap to the underlying one of said marginal portions and said cement layer.

6. The joint of claim 5 wherein each of said core panels includes a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paper facing layer, said recessed marginal surfaces taper edgewise toward the rear sides of said core panels and have a minimum width to depth ratio of about 3.75/1, and each of said decorative sheets includes an inner cloth backing layer laminated to said paper facing layer and an outer polyvinyl chloride layer forming a decorative front wall surface.

This invention relates to simulated monolithic predecorated wall construction, and more particularly to new and improved predecorated wallboards for forming such wall construction, new and improved joints incorporating such wallboards for forming practically invisible seams, and new and improved methods of forming such joints.

In simulating monolithic wall construction employing wallboards, such as gypsum boards, the two most common techniques are as follows. In one technique, individual wallboard panels are first installed over the underlying wall structure, such as studs. This is followed by treating the joints with joint cement to produce a continuous surface, and then application of the decorative coating, such as vinyl plastic sheets, in substantially the same manner as wallpaper, thereby requiring formation of additional joints or seams between the plastic sheets. This technique is both time consuming and expensive because of the various separate operations required.

The other technique involves installation of predecorated wallboards, followed by covering of the joints with prefabricated strips or battens either of contrasting decorative appearance or predecorated to simulate the predecorated surface of the wallboards. While this technique represents an improvement over the first technique from a time and expense standpoint, it suffers in that the finished wall surfaces are far from monolithic in appearance.

Accordingly, a primary object of the present invention is to utilize the best features of these two prior techniques, while eliminating their disadvantages, to produce simulated monolithic predecorated wall construction having a true monolithic appearance. To this end, the present invention employs new and improved predecorated wallboards in a new and improved manner to produce new and improved joints having practically invisible seams along the wallboards in just one joint treatment operation, for the desired monolithic appearance of the finished wall surface. As a consequence, the present invention eliminates the separate operations of installation of undecorated wallboards followed by decoration thereof, and combines the separate wallboard and decorative coating joint treatments, all as required by the first technique, while eliminating the separate installation of the joint covering strips or battens of the second technique, as well as their disruptive effect on the desired monolithic appearance.

Another object of the present invention is to provide such new and improved predecorated wallboards which are so constructed and designed as to form with adjacent so predecorated wallboards new and improved joints having practically invisible seams.

Another object is to provide such new and improved predecorated wallboards which are so constructed and designed as to permit installation thereof directly over metal studs in compliance with the American Standards Association requirement of mechanical fasteners along the joints between adjacent wallboards, while permitting the formation of new and improved finished joints which hide the heads of such fasteners.

A further object is to provide such new and improved joints having practically invisible seams by incorporating such new and improved predecorated wallboards and a hardened joint cement layer.

Still another object is to provide new and improved methods of forming such new and improved joints by locating such new and improved predecorated wallboards and treating the joints therebetween in such a manner as to produce such practically invisible seams.

Additional objects and advantages of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings, wherein:

FIG. 1 is a fragmentary perspective view of a predecorated wallboard embodying the invention;

FIG. 2 is a fragmentary perspective view of simulated monolithic predecorated wall construction incorporating such wallboard and illustrating flat, inside corner and outside corner joints prior to joint treatment;

FIG. 3 is a greatly enlarged fragmentary section taken on line 3--3 of FIG. 1 and illustrating the wallboard as produced;

FIG. 4 is an enlarged fragmentary horizontal section taken through the encircled portion of the flat joint shown in FIG. 2;

FIGS. 5 and 6 are views similar to FIG. 4, but taken during and following the joint treatment operation, respectively;

FIG. 7 is an enlarged, fragmentary horizontal section taken through the encircled portion of the outside corner joint shown in FIG. 2;

FIGS. 8 and 9 are views similar to FIG. 7, but taken during and following the joint treatment operation, respectively;

FIG. 10 is an enlarged, fragmentary horizontal section taken through the encircled portion of the inside corner joint shown in FIG. 2;

FIGS. 11 and 12 are views similar to FIG. 10, but taken during and following the joint treatment operation, respectively, and

FIG. 13 is an enlarged, fragmentary horizontal section taken through the encircled portion of FIG. 2, and illustrates a joint between a wallboard and an underlying stud intermediate the wallboard edges.

Referring to the drawings, and particularly FIGS. 1 and 3, a predecorated wallboard constituting a preferred embodiment of the invention is indicated generally at 10. This wallboard preferably includes a core panel 12 of elongated, generally rectangular shape, and a decorative sheet 14 laminated to the front side of such core panel throughout its length. Core panel 12 has on its front side a substantially flat, central surface 16 arranged between opposite recessed marginal surfaces 18 which preferably taper edgewise toward rear surface 20, and which extend from surface 16 to opposite longitudinal edges 22 of the core panel. Decorative sheet 14 is laminated only to flat surface 16 by suitable adhesive layer 24 during manufacture of wallboard 10, and includes a shorter flap 26 extending over one of marginal surfaces 18 at least adjacent, and preferably terminating substantially flush with, one edge 22 of core panel 12. Sheet 14 also includes a longer flap 28 which extends over the opposite marginal surface 18 at least beyond the opposite edge 22 of the core panel to overlap with an adjacent shorter flap 26, such as shown in FIG. 5, and preferably around such opposite longitudinal edge onto the rear side 20 of such panel. Flap 28 is removably and temporarily secured to such rear side 20 by suitable means such as adhesive bead 30 during manufacture of the wallboard, and which bead preferably is coextensive with the length of panel 12.

From a constituent standpoint, wallboard 10 has the following preferred construction. The adhesive layer 24 laminating decorative sheet 14 to flat surface 16 and adhesive bead 30 are of a dextrine type, e.g. a borated dextrine. Core panel 12 is composed of a set cementitious, and preferably gypsum, core 32 enclosed on its two opposite sides and two longitudinal edges with a fibrous, and preferably paper, facing layer 34. Decorative sheet 14 includes an inner fibrous, and preferably cloth, backing layer 36, which is laminated to the paper facing layer 34 forming flat surface 16, and an outer plastic, and preferably polyvinyl chloride, layer 38 forming a decorative front wall surface. The fibrous backing layer 36 is provided to give dimensional stability to the outer plastic layer 38 during manufacture of composite sheet 14, during lamination of such sheet to core panel 12, and during cutting of flaps 26, 28 when forming joints. Plastic layer 38 may be embossed, printed or otherwise decorated to provide the desired decorative outer or front wall surface.

From a dimensional standpoint, wallboard 10 has the following preferred construction. The overall nominal dimensions of the board typically are 4 feet in width, 7 to 10 or more feet in length, and one-fourth to five-eighths inch in thickness. The decorative sheet 14 is laminated to flat surface 16 over a 40 inch width, thereby providing shorter flap 26 with a width of about 4 inches and longer flap 28 with a width of about 5 1/4 inches. The fibrous backing layer 36 of decorative sheet 14 is about three times the thickness of plastic layer 38, typical thickness dimensions being 12 mils and 4 mils respectively. The typical width of each marginal surface 18 is about 2 1/2 inches, which ordinarily leaves about 1 1/2 inches at each marginal portion of flat surface 16 unadhered to overlying sheet 14. This is for facilitating the joint treatment operation to be described below, by permitting the flaps on adjacent panels to be folded or peeled back and away from the joint between two adjacent core panels, for free and unemcumbered entry of a broad knife in applying joint cement and for applying adhesive to the underside of the flaps. However, the extent of such unadhered area between flat surface 16 and sheet 14 is not critical.

Typically, each tapering marginal surface 18 has a width of about 2 1/2 inches and a depth of about 0.06 inch. However, such width may vary from about 0.75 inch to about 4 inches, while such depth may vary from about 0.015 inch to about 0.2 inch. Thus, the preferred width to depth ratio for facilitating fastening of core panel 12 to the underlying stud or the like structure and for facilitating the joint treatment is about 42/1, while the minimum permissible ratio is about 3.75/1.

This substantially greater width then depth characteristic of each tapering marginal surface 18 is an important feature of the invention for providing an adequate surface through which fasteners may be driven adjacent the joint between two adjacent wallboards 10, particularly in installing such wallboards directly over metal studs, because it is required by the American Standards Association that when wallboards are so installed, they must be mechanically fastened along such joints. A typical predecorated wallboard now in commercial use is provided with a chamfered longitudinal edge of about three-sixteenths inch in both width and depth. This does not provide a sufficient bearing surface for the heads of fasteners to be driven into such metal studs at such joints. Accordingly, when using such typical chamfered predecorated wallboards, a double wall construction must be used to comply with this A.S.A. requirement.

In contrast, the inventive predecorated wallboard 10, by reason of marginal surfaces 18 providing a recessed, and preferably tapering, width to depth ratio of at least 3.75/1 with a minimum width of about 0.75 inch, presents an adequate bearing surface for the fastener heads in compliance with such A.S.A. standard, and eliminates the need for such double wall construction. This is the only predecorated wallboard known to us to satisfy such standard, while permitting joint treatment to hide such fastener heads and produce practically invisible seams for the desired monolithic wall surface appearance.

While the inventive wallboard 10 obviously may be applied over existing wall surfaces or any other suitable skeletel supporting wall structure, such as the typical wooden studs, it is especially useful, as noted above, for direct application to metal studs, such as those indicated generally at 40 in the drawings. Referring particularly to FIG. 2, a typical simulated monolithic predecorated wall construction incorporating such wallboards 10 is shown as including, from left to right, a flat joint, an inside corner joint and an outside corner joint. At each joint, such as illustrated in greater detail in FIGS. 4, 7 and 10 respectively, adjacent inventive wallboards 10 are secured along their joints to the underlying metal studs 40 by suitable fasteners, such as sheet metal screws 42, with the heads of such screws dimpling the paper facing layer 34 on the front side of each core panel 12.

In order to maintain a substantially continuous decorative surface along the joints formed between such studs 40 and the wallboards intermediate the longitudinal edges of such wallboards, the rear surfaces 20 of such wallboards are secured to such studs 40 by means of adhesive layer 44, as shown in greater detail in FIG. 13. This adhesive layer may be of any suitable type which is compatible with and adheres to the materials of the wallboard and the underlying supporting wall structure, e.g. paper and metal. Preferably, layer 44 is of the "modified" contact type adhesive, which has sufficient strength on contact to support wallboards 10 in the desired position, but does not take a permanent set for an extended period of time, so as to permit adjustment of the positions of such wallboards, if necessary.

In practicing the inventive method of forming various joints in simulated monolithic predecorated wall construction, such as shown in FIG. 2, it is preferred that the various wallboards 10 first be installed over studs 40, followed by treating and finishing the various joints, e.g. by moving clockwise in FIG. 2. Generally speaking, for each of the illustrated and other joints, the corresponding wallboards are arranged adjacent each other by locating their core panels 12 so that one panel has one longitudinal edge substantially abutting the adjacent longitudinal edge or side of the other panel and one side substantially flush with the adjacent side or edge of the other panel; by filling the space between one flap, namely flap 26, and the underlying marginal surface with joint cement extending beyond such flap to substantially the level of flat surface 16 and allowing the joint cement to form a hardened layer; by adhering both flaps, such as 26 and 28, to the hardened cement layer and each other, with the flaps overlapping over marginal surface 18 underlying such one flap 26, by cutting through the overlapping portions of both flaps over the hardened cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap to cause such one flap 26 to terminate short of its panel's longitudinal edge 22 over the underlying marginal surface 18, and by readhering the remainder of the overlying flap to cause the other flap, such as 28, to extend over the exposed surface of the hardened cement layer into substantially edge abutting and flush relationship with the one flap 26, to form a practically invisible longitudinal seam along the joint.

After forming either a flat joint, an outside corner joint, or an inside corner joint, such as those shown in the drawings, additional joints readily may be formed on either or both sides of the originally formed joint, inasmuch as each wallboard 10 originally includes a longer flap, such as 28 and a shorter flap, such as 26. Hence, prior to or following formation of a particular joint, such as the flat joint shown in FIGS. 4-6, wherein longer flap 28 on the left hand panel 12 and shorter flap 26 on the right hand panel 12 have been arranged in the desired substantially abutting and flush relationship, the left hand core panel 12 still has a shorter flap 26 (FIG. 3) which is adapted to be arranged in the desired relationship with another flap, such as longer flap 28, on a third panel. At the same time, longer flap 28 (FIG. 3) on the right hand core panel 12 (FIG. 4) is adapted to be arranged in the desired relationship with a shorter flap 26 on a fourth panel. Thus, merely by repeating the aforesaid locating, filling, adhering, cutting and readhering steps, additional joints are likewise formed with practically invisible longitudinal seams.

Referring now to FIGS. 4-6 in particular, the desired substantially flat joint is formed by locating and fastening adjacent panels 12 on stud 40 by screws 42 so that one panel has one longitudinal edge 22 arranged in substantially abutting relationship with the adjacent longitudinally edge of the other panel and its front side substantially flush with the front side of the other panel, with the adjacent recessed marginal surfaces 18 tapering edgewise toward each other and rear surfaces 20. Previously, as in forming each joint, flap 28 is removed from rear surface 20 (FIG. 3), and both adjacent flaps 26, 28 are folded back out of the way to expose the unadhered marginal portions of flat surfaces 16 as well as recessed marginal surfaces 18, somewhat as shown in FIG. 4, and actually secured temporarily to sheet 14, preferably by masking tape (not shown), to facilitate the joint treatment operation. The space between each marginal surface 18 and each flap 26, 28 is filled with joint cement substantially to the level of flat surfaces 16 and allowed to form a hardened layer 46.

Any suitable joint cement may be employed for this purpose, in forming each joint, but it is preferred that a quick setting type of cement be used, rather than a slow drying type, in order to speed the joint treatment and finishing operation. A typical joint cement of the quick setting type, which has been found to be particularly useful in practicing the present invention, is described in Canadian Pat. No. 715,620.

After cement layer 46 has sufficiently hardened, flaps 26, 28 are unfolded and adhered to the exposed surface of such layer, the marginal portions of surfaces 16 and to each other in any suitable manner, but preferably by applying suitable adhesive paste at least to the undersides of the flaps. One suitable adhesive paste which has been found to be particularly useful in practicing the invention, is wheat paste. Flaps 26, 28 are adhered, as noted above, with such flaps overlapping over marginal surface 18 underlying flap 26. As shown in FIG. 5, flap 28 overlaps flap 26, although the latter could overlap the former.

The next step involves cutting through the overlapping portions of both flaps 26, 28, such as along line L, shown in FIG. 5, by means of any suitable cutting instrument. Next the overlapping marginal edge portions, such as 28a, of overlying flap 28, and the overlapped marginal edge portion, such as 26a, of underlying flap 26, are removed, thereby causing flap 26 to terminate short of the adjacent longitudinal edge 22 of right hand core panel 12. Preferably, after removing marginal edge portion 28a, flap 28 is peeled or folded back to facilitate stripping of marginal portion 26a.

Following such removal, the remaining portion of flap 28 is readhered to the underlying marginal portion of left surface 16 and layer 46, such as shown in FIG. 6, and, if necessary, the remaining portion of flap 26 is readhered, to cause flap 28 to extend beyond edge 22 of left hand panel 12 and over the exposed surface of cement layer 46 formerly covered by marginal edge portion 26a into the substantially edge abutting and flush relationship with flap 26, to form the desired practically invisible seam S of the finished joint. If necessary, any adhesive paste which may have been removed by striping marginal portion 28a or 26a may be reapplied prior to readhering flap 28 or 26, and any excess paste may be wiped off.

Application of the inventive method to formation of a typical outside corner joint, such as shown in FIGS. 7-9, involves the same sequence of steps, but with the following differences. As so often happens when coming to a corner, the wallboard is too long, and this is the situation shown in FIGS. 7-9. Hence, prior to fastening the vertically illustrated wall panel 10 to the underlying studs 40, it is necessary to cut such wallboard to the appropriate length. This often involves, as shown in FIG. 7, cutting back core panel 12 and stripping a flap, such as 28, back from the underlying core panel 12 to such an extent that no recessed marginal surface 18 is left. Thus, former edge 22 is converted into newly formed longitudinal edge 50, and flap 28 is converted to stripped back flap 52.

Nevertheless, in forming such an outside corner joint, the method involves basically the same locating step as in FIGS. 4-6, except that the two core panels 12 are located so that one panel, such as vertical panel 12 in FIGS. 7-9 has one longitudinal edge, such as 50, arranged in substantially abutting relationship with the rear side of horizontal panel 12, and its front side substantially flush with the adjacent longitudinal edge 22 of horizontal panel 12, to form an angle of more than 180° between such front sides, about 270° being shown. At the same time, one panel, such as horizontal panel 12, has on its front side a recessed tapering marginal surface 18 extending from flat surface 16 to longitudinal edge 22 adjacent vertical panel 12, with sheet 14 on horizontal panel 12 having flap 26 terminating substantially flush with edge 22, while sheet 14 on vertical panel 12 has flap 52 extending beyond longitudinal edge 50.

Next, as shown in FIGS. 7-9, the space between flap 26 and marginal surface 18 is filled with joint cement extending to edge 22 to substantially the level of flat surface 16 on horizontal panel 12, and actually beyond the edge of flap 26 after being cut, as shown in FIG. 9. In the embodiment shown, the resulting hardened cement layer 54 is of generally right triangular cross section, to form the preferred sharp corner, as opposed to the substantially isosceles triangular cross section of layer 46 in FIGS. 4-6. Flaps 52 and 26 are adhered to the underlying surface of cement layer 54 and to each other, as before, except that flap 52 is first extended over edge 22 of horizontal panel 12 and turned over layer 54 to form the underlying flap, while flap 26 forms the overlying flap, as shown in FIG. 8. The purpose of reversing the relative positions of such flaps, as compared to that shown in FIGS. 4-6, is to avoid, as much as possible, disturbing the desired, preferably sharp corner shape of cement layer 54. After cutting through both flaps along a line such as L ₁ , marginal portions 26a and 52a are removed, whereupon the readhered remaining portion of flap 26 extends into substantially abutting and flush relationship with the remaining adhered portion of flap 52, to form the desired, practically invisible longitudinal seam.

Referring to FIGS. 10-12, a typical inside corner joint is shown therein, wherein it was found to be necessary to cut down the length of wallboard 10 forming the right half portion of the flat joint shown in FIGS. 4-6, in order to form the desired inside corner joint, just as it was found necessary to cut down the length of the wallboard 10 forming the left hand or upper portion or the outside corner joint shown in FIGS. 7-9. To this end, it was necessary to strip longer flap 28 of the upper or horizontal wallboard 10 in FIG. 10 back along flat surface 16, and to entirely remove marginal surface 18, in order to form a new longitudinal edge 56 on such horizontal wallboard. Thus, flap 28 is necessarily converted to flap 58 in FIG. 10.

After such stripping and edge forming operation, the panels are located and fastened to studs 40 in the manner shown, it being noted that the head of screw 42 passing through horizontal panel 10 dimples paper layer 34 forming flat surface 16, just as in the vertical panel of FIG. 7, so as to avoid disruption of the desired continuous surface effect produced by the invention.

In forming an inside corner joint, panels 12 are located and fastened to studs 40 so that one panel, such as horizontal panel 12 in FIG. 10, has one longitudinal edge, such as 56, arranged in substantially abutting relationship with the front side of the other panel, such as vertical panel 12, and its rear side substantially flush with the adjacent longitudinal edge 22 of vertical panel 12, to form an angle of less than 180° between the front sides of the panels, 90° being shown. At the same time, one panel, such as vertical panel 12, has a recessed marginal surface 18, while sheet 14 on such vertical panel has a flap, such as 26, of such a length as to terminate substantially flush with edge 22, while flap 58 is long enough to extend beyond edge 56.

The space between marginal surface 18 and flap 26 is filled with joint cement which extends to the front side of horizontal panel 12, which is beyond flap 26 after being cut, as shown in FIG. 12, to substantially the level of flat surface 16 on vertical panel 12. Once again, upon hardening, the resulting cement layer 60 is of generally right triangular cross section to form the desired sharp inside corner, and flap 58 is first turned over the exposed surface of layer 60 to form the underlying flap to avoid disturbing such corner.

Following the adhering step, the overlapping flap portions are cut along line L ₂ , whereupon marginal portions 26a and 58a are removed, with the remaining portion of flap 26 being readhered to extend into the desired substantially abutting and flush relationship with the remaining portion of flap 58, and thereby form the desired practically invisible longitudinal seam S ₂ , shown in FIG. 12.

It now will be seen how the invention accomplishes its various objects, and the numerous advantages of the invention likewise will be apparent. While the invention has been described and illustrated herein by reference to certain embodiments, it is to be understood that various changes and modifications may be made therein by those skilled in the art, without departing from the inventive concept, the scope of which is to be determined by the appended claims.