Static structures (e.g. – buildings) – Intersection of wall to floor – ceiling – roof – or another wall – With revealed embedded protector
Reexamination Certificate
2002-12-20
2004-04-20
Canfield, Robert (Department: 3635)
Static structures (e.g., buildings)
Intersection of wall to floor, ceiling, roof, or another wall
With revealed embedded protector
C052S256000
Reexamination Certificate
active
06722092
ABSTRACT:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
(Not applicable)
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to drywall construction, and more particularly to an improved corner bead strip with paper wings.
(2) Background Information
Current building construction utilizes sheets of drywall, commonly referred to as “wallboard,” to form the surfaces of interior walls of buildings. Drywall, or wallboard, is typically formed of sheets of plaster sheathed in an outer wrapping of heavy construction paper.
In wallboard construction, joints between adjacent sheets of drywall are usually covered by a paper tape extending lengthwise along the joint. The conventional drywall tape is provided in narrow elongated strips of porous paper wound into rolls. The drywall tape is applied to the joints, and then covered with wet plaster or “mud”. The plaster is feathered and smoothed along the edges of the tape to conceal the tape edges and form a smooth unmarred surface where the wallboard adjoins.
It is often necessary to cut the wallboard to form a corner, which thereby exposes the plaster contained between the heavy paper sheets. This exposed plaster tends to crumble unless these edges are protected. To finish exterior corners in wallboard construction, metal corner beads and bullnose beads are typically installed. Such corner beads are conventionally formed by roll-forming from an elongated strip of sheet metal, and provide a round nose with two mounting flanges extending at substantially right angles from the opposing sides of the nose. These mounting flanges are often knurled or embossed to provide a rough surface so that the joint compound will adhere when the corner is finished. Similarly, metal trim is used to protect and finish a wallboard edge at window and door jams, while expansion joints are inserted between sheets of wallboard at predetermined intervals within buildings.
The corner bead is installed by securing the mounting flanges along the surface of the drywall panels adjacent to the corner by nails or the like. Wet plaster is then smoothed into place to cover the metal flanges, and edges of the plaster are smoothed and feathered to cover and conceal the metal edges.
Another type of corner bead is referred to as a “tape-on” bead. Tape-on corner beads utilize a strip of paper covering the exterior surface of the metal corner angle, with wings projecting outwardly from the legs of the corner angle. Wet plaster or joint cement secures these paper wings to the drywall, to secure the corner bead in position, rather than using nails or other fasteners. Wet plaster or joint cement for finishing the corner will normally adhere significantly better to the paper cover strip of tape-on beads, than to the exposed metal of conventional nail-on beads. Nail-on beads are also typically more susceptible to developing crack lines along the outer edges of the flanges, than are tape-on beads. In addition, tape-on beads are more tolerant of dimensional and geometric changes in the underlying construction framing than are nail-on beads with their rigid mechanical attachment to the construction framing.
One of the main problems with prior art tape-on bead is the use of standard joint/drywall tape on the bead. Such drywall tape is very fibrous, which is good for bond strength, but poor for appearance. During the application of joint cement over the tape, to adhere the corner bead to the drywall, fibers will project and protrude with only minimal contact by the application tools. These fibers will ball up during the course of sanding of the joint cement for the final finish, thereby detracting from the finished appearance of the corner.
One method for improving protection against adverse abrasion of this paper strip is disclosed in U.S. Pat. Nos. 5,613,335 and 5,836,122, both to Rennich et al. These patents disclose a paper bead (tape-on bead) utilizing a paper layer which is uniformly impregnated throughout its thickness with latex or similar strengthening compound with a high wet strength so as to make the paper strip resistant to scuffing and abrasion throughout its thickness. This impregnated stock paper would have a high pick resistance or surface fiber bond, and would effectively inhibit separation of surface fibers during application on wallboard, thereby providing a good finished appearance in installation. However, the applicants herein have found that paper of this type, which is impregnated with latex or the like, exhibits poor joint compound bonding properties, as applied under the ASTM bond strength tests.
More specifically, ASTM C-475-01 recites a variety of standards for joint tape, including the following three standards:
4.3.3 Tensile Strength—Shall be not less than 30 lbf/in. (524 N/mm) in the cross direction.
4.3.4 Dimensional Stability—Shall expand not more than 0.4% lengthwise and not more than 2.5% crosswise.
4.4.1 Bond—between the joint tape and joint compound shall be not less than 90%.
These terms are used throughout this application, and are intended to refer to the standards set forth in ASTM C-475-01. The test method for determining bond strength or the “peel bond” percentage recited in ASTM C-475-01, is set forth in ASTM C-474-01. Section 3.2.1 defines “bond” as the “quality of adhesion between the paper joint tape and joint compound. Thus, the inventors herein have also described this as the “peel bond”, or the amount of force required to peel the joint tape from the joint compound.
Section 13 of ASTM C-474-01 describes the methodology for calculating the percent bond set forth in ASTM C-475-01. The pertinent portions of that section are set forth herein in more detail, for a better understanding of the bond percent. First, the apparatus used in the sampling are described, and include “feeler gage strips”, and an “overlay transparency grid”. The feeler gage strips are described in 13.4.1 as being “12 in. (300 mm) long, ½ in. (13 mm) wide, and 0.025 in. (0.64 mm) thick with a small hole drilled in one end. The overlay transparency grid is defined in 13.4.4 as “a transparent photocopy of 10 by 10 divisions/in. graph paper. An area 2 by 5 in. (51 by 127 mm) enclosing 1000 square divisions is outlined.
The Procedure for determining percent bond is described in Section 13.5 as follows:
13.5.1 Place two feeler gage strips parallel to each other about 4 inches (102 mm) apart and fasten to the face of the gypsum wallboard with a thumb tack through the hole in the end.
13.5.2 Using the steel reinforced broad knife, apply an amount of joint compound sufficient to cover the area between the feeler gage strips. Spread the specimen evenly between the feeler age strips leaving the specimen slightly thicker than the strips.
13.5.3 Center a 12-in. (305 mm) length of paper tape in the specimen. Press one end of the tape into the specimen and hold it in place.
13.5.4 Embed the tape by applying two or three pressure strokes with the steel-reinforced broad knife. Wipe away from the end being held so the excess joint compound is squeezed out.
NOTE 8—The thickness of the joint compound plus the tape is about 0.025 in. (0.64 mm).
13.5.4.1 Carefully remove the feeler gages before drying.
13.5.5 Allow the test assembly to dry to constant weight in an atmosphere of 75+/−5° F. (24+/−2° C.) and 50+/−5% relative humidity.
13.5.6 When the test assembly is dry, use a sharp knife to make a cut across and perpendicular to the tape 3½ in. (90 mm) from one end. Make a second cut 5 in. (130 mm) from and parallel to the first cut. Make two diagonal cuts across the tape connecting the opposite corners of the 5-in. (130 mm) section. With the tip of the knife, peel back the tabs formed by the “X” cuts and pull up sharply.
13.5.6.1 Make a second test by repeating 13.5.6 below the first test.
13.5.7 Using a sharp pencil, lightly outline the area where fiber remains attached to the compound. Align the overlay transparency grid so that the grid outline matches the 2 by 5-in.
Kunz Roland
Rantilla Roy R.
Canfield Robert
Phillips Manufacturing Co.
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