Wallboard taping process and apparatus therefor

Abstract: An apparatus for taping joints between pieces of wallboard comprising a taping head, slidingly contactable with a wall, for substantially simultaneously applying a first layer of a joint compound to a joint between pieces of wallboard, embedding a wallboard tape in the first layer of the joint compound, and overcoating the embedded wallboard tape with at least one additional layer of the joint compound; a handle (69), connected to the taping head, for supporting the taping head, the handle (69) being manually graspable by an operator, the handle having a fluid conduit formed therein for passing joint compound to the taping head; a tape supply (71) mounted on the handle for supplying wallboard tape to the taping head; a backpack (3), wearable by the operator, for supporting a supply of the joint compound and for producing a pressurized stream of the joint compound; and a flexible connecting means (57) for fluidically interconnecting the backpack (3) and the fluid conduit to pass the pressurized stream of the joint compound from the backpack to the fluid conduit.

Description: The present invention is directed to a method of taping joints between adjacent pieces of wallboard and an apparatus for effecting such taping of the joints, and concerns a method and apparatus whereby a finished joint between adjacent pieces of wallboard may be completed in one step according to the preamble of claim 1 and the preamble of claim 14. Description Of The Prior Art: Wallboard (also known as drywall) has become the dominant material in the production of interior building partitions. In particular, interior building partitions generally comprise a studwall of spaced parallel vertical members (studs) which are used as a support for preformed panels (wallboard) which are attached to the studwall by screws, nails, adhesive or any other conventional attachment system. Obviously, joints exist between adjacent preformed panels. In order to provide a continuous flat surface to the wall, it is necessary to "finish" the joint between adjacent panels. Generally, such "finishing" requires the building up of multiple layers of a mastic material (joint compound) and the blending of this joint compound into the panel surface so as to form the desired flat and contiguous wall surface. In order to facilitate this finishing of the joints, most manufacturers bevel the longitudinal edges of the wallboard panels so as to allow a buildup of mastic material which will then match the level of the major surface area of the preformed panel. Typically, the buildup of the mastic material in the joint area comprises the application of a first layer of mastic material, the embedding of a wallboard tape (for example a paper tape or a fiberglass tape) in the first layer of mastic material and then the overcoating of the tape with one or more, generally two layers of additional mastic material. This finishing of the joints is a time consuming process, since it is generally necessary to wait 24 hours between each application of a coat of mastic material in order to allow the coat to dry before the application of an additional layer of mastic material. Moreover, it is then necessary generally to sand the joint area so as to produce a finish which will match the major portion of the surface area of the wallboard panels. The "finishing" process thus is both time-consuming and labour-intensive. In this regard, numerous attempts have been made to speed up and/or reduce the labour involved in the finishing products. In this regard, attention is directed in particular to US Patent No. 4 127 434 which discloses apparatus for dry wall taping comprising a taping head for applying joint compound and wallboard tape to a wallboard joint. A handle which is grasped by the operator and which supports the head, includes a fluid conduit for passing jointing compound to the head. A supply of tape for the head is mounted on the handle. The operator wears a backpack which supports a supply of jointing compound and provides a pressurised supply thereof to the conduit in the handle. Despite the great efforts which have been applied to reduce the labour and time involved in wallboard finishing, there is still a marked need for an efficient and useful tool which is easy to operate and which will allow a one-step finishing of wallboard. The present invention provides apparatus for taping joints between pieces of wallboard comprising: a taping head slidingly contractable with a wall, adapted to apply joint compound and wallboard tape to a joint between pieces of wallboard; a handle, connectable to said taping head, adapted to support said taping head, said handle being manually graspable by an operator, said handle having a fluid conduit (73, 113) formed therein adapted to pass joint compound to said taping head; a tape supply, mounted on said handle adapted to supply wallboard tape to said taping head; a backpack, wearable by said operator, adapted to support a supply of said joint compound and to produce a pressurized stream of said joint compound; a flexible connector adapted to fluidically interconnect said backpack and said fluid conduit to pass said pressurized stream of said joint compound from said backpack to said fluid conduit; said apparatus characterized in that said taping head is adapted to substantially simultaneously apply a first layer of a joint compound to a joint between pieces of wallboard, embed a wallboard tape in said first layer of said joint compound and overcoat said embedded wallboard tape with at least a second layer of said joint, said taping head comprising a first support plate attached to said handle, a guide, attached to said first support plate, adapted to guide a wallboard tape of predetermined width while being applied to a joint, a first orifice, attached to said first support plate, adapted to feed a first layer of joint compound to a surface of said wallboard tape intermediate said joint and said wallboard tape, said first orifice fluidically connected to said fluid conduit, a second support plate releasably attachable to said handle, biasing means attached to said second support plate, adapted to yieldably urge said wallboard tape and, hence, said first layer of joint compound, into contact with said wall, when said taping head is in contact with said wall, to embed said wallboard tape in said first layer of joint compound, a second orifice, formed in said second support plate proximate said first support plate, adapted to feed a second layer of joint compound atop said wallboard tape to overcoat said wallboard tape with said second layer of said joint compound, said second orifice having a width greater than said wallboard tape, said second orifice being centered, widthwise, with respect to said guide, a first passage, formed in said second support plate, adapted to fluidically connect said second orifice and said fluid conduit, a first gate, pivotally connected to said second support plate for pivotal movement between a first position and a second position, said first gate preventing flow of joint compond through said second orifice when in said first position and allowing flow of joint compound through said second orifice when in said second position. The invention also provides a method for taping joints between piece of wallboard comprising applying a wallboard tape to tape joints between pieces of wallboard which have had a joint compound applied thereto, said method characterized in that it comprises: substantially simultaneously (a) applying a first layer of a joint compound to a joint between pieces of wallboard, said first layer of said joint compound having a first predetermined width, said first layer of said joint compound being substantially cantered, widthwise, on said joint; (b) embedding a wallboard tape in said first layer of said joint compound, said wallboard tape having a width substantially equal to said first predetermined width, said wallboard tape being substantially centered, widthwise, on said joint; (c) overcoating said embedded wallboard tape with at least one additional layer of said joint compound, said at least one additional layer of said joint compound having a width greater than said first predetermined width, said at least one additional layer of said joint compound being substantially centered, widthwise, on said joint. The second layer of joint compound may have a predetermined width greater than the width of the first layer of joint compound, and it may be overcoated with a third layer of joint compound, such third layer having a predetermined width greater than that of the second layer and being centred widthwise on the joint. The method may further comprise the step of imprinting a surface pattern on the third layer of joint compound, and preferably the surface pattern matches a surface pattern on the wallboard. The invention also provides a joint composition to be used with the apparatus or method of the invention, as set out above, comprising 35 to 60% by weight of a gypsum base plaster; 30 to 70% by weight of a wetting agent comprising 0 to 30% by weight of water and an alcohol selected from the group consisting of methyl alcohol, ethyl alcohol and propyl alcohol; and 10 to 25% by weight of polyvinyl acetate. In contrast with the joint composition disclosed in DE 3 542 262, the composition of the invention contains a particular vinyl polymer (vinyl acetate) and a specific wetting agent (methyl, ethyl or propyl alcohol) falling within a specified concentration. It is quick-setting, so as to allow for substantially simultaneous application of multiple layers of joint compound to a given joint. The water-alcohol wetting agent preferably comprises 37 to 56% by weight, and more preferably 42% by weight, of the alcohol component. Preferably the joint compound comprises about 45% by weight of calcium sulphate, about 35% by weight of room temperature evaporable alcohol, about 10% by weight of polyvinyl alcohol, about 5% by weight of polyvinyl acetate, about 3% by weight talc and about 2% by weight mica. In a preferred embodiment, the gypsum base plaster comprises from about 40-70, more preferably 45-60, most preferably 55% by weight of calcium sulfate, up to 10%, most preferably 6.5% by weight of calcium carbonate, up to 5%, more preferably about 2% by weight of silica sand, up to 6%, most preferably about 4% by weight of starch, small amounts of conventional drying accelerators for the gypsum base plaster, 0-10% by weight of talc and 0-10% by weight of mica. The total amount of talc plus mica constituting from about 4-20% by weight. Preferably, the composition of the present invention contains from about 0 to 5% of polyvinyl alcohol, preferably about 1%. The composition of the present invention contains an adhesive material which preferably comprises a polyvinyl acetate in an amount of from about 10 to 25, most preferably 14% by weight. Applicant discovered that upon application to a surface of a conventional plaster containing polyvinyl chloride and water as the wetting agent, the polyvinyl chloride quickly forms an outer skin through which the water must migrate in order for the plaster to completely dry and harden. As a consequence, it becomes necessary in construction projects to maintain an ambient temperature of at least 55 o F in the room where the plaster is to be applied. The cost of heaters, fuel, and labor to maintain this temperature adds significantly to the cost of construction. Applicant unexpectedly discovered that when a plaster comprises a gypsum base, an alcohol-water wetting agent, and polyvinyl acetate, the wetting agent migrates much faster through the skin formed on the polyvinyl acetate, than the water which migrates through the skin on polyvinyl chloride in conventional gypsum plasters. This accelerated drying rate of the composition of the present invention was unexpectedly found to be unaffected by temperature over a relatively wide range. For example, the composition of the present invention can be applied satisfactorily at temperature of from about 10-20 o F. It was also unexpectedly discovered that the dried composition of the present invention absorbs conventional paints, including both water and oil base paints, at a rate approximating the absorption rate of the paper used on the outer surface of conventional drywall. As a result, satisfactory painting of the surface of a wall finished with the composition of the present invention can be accomplished with only one coat of paint, thus eliminating the need for a primer and a second top coat. In addition, applicant has found that the apparatus described herein can be satisfactorily cleaned with a cleaning solvent comprising an aqueous mixture of zinc chloride, optionally containing a minor amount of alcohol. The compositions of the present inventions can be used in a process comprising the substantially simultaneous steps of: (a) applying a first layer of the joint compound to a joint between pieces of wallboard, the first layer of the joint compound having a first predetermined width, the first layer of the joint compound being substantially centered, widthwise, on the joint; (b) embedding a wallboard tape in the first layer of the joint compound, the wallboard tape having a width substantially equal to the first predetermined width, the wallboard tape being substantially centered, widthwise, on the joint; (c) overcoating the embedded wallboard tape with at least one additional layer of the joint compound, the at least one additional layer of the joint compound having a width greater than the first predetermined width, the at least one additional layer of the joint compound being substantially centered, widthwise, on the joint. According to the present invention there is also provided an apparatus for taping joints between pieces of wallboard, comprising a taping head, slidingly contractable with a wall, for substantially simultaneously applying a first layer of a joint compound to a joint between pieces of wallboard, embedding a wallboard tape in the first layer of the joint compound and overcoating the embedded wallboard tape with at least one additional layer of the joint compound; a handle, connected to the taping head, for supporting the taping head, the handle being manually graspable by an operator, the handle having a fluid conduit formed therein for passing joint compound to the taping head; a tape supply mounted on the handle for supplying wallboard tape to the taping head; a backpack, wearable by the operator, for supporting a supply of the joint compound and for producing a pressurized stream of the joint compound; a flexible connection for fluidically interconnecting the backpack and the fluid conduit to pass the pressurized stream of the joint compound from the backpack to the fluid conduit. The taping head may comprise a first support plate, attached to the handle; a guide means, attached to the first support plate, for guiding a wallboard tape of predetermined width being applied to a joint; first orifice means, attached to the first support plate, for feeding a first layer of joint compound to a surface of the wallboard tape intermediate the joint and the wallboard tape, the first orifice means fluidically connected to the fluid conduit means; a second support plate, releasably attachable to the handle; biasing means, attached to the second support plate, for yieldably urging the wallboard tape and, hence, the first layer of joint compound, into contact with the wall, when the taping head is in contact with the wall, to embed the wallboard tape in the first layer of joint compound; second orifice means, formed in the second support plate proximate the first support plate, for overcoating the wallboard tape with a second layer of the joint compound, the second orifice means having a width greater than the wallboard tape, the second orifice means being centered, widthwise, with respect to tie guide means; first passage means, formed in the second support plate, for fluidically connecting the second orifice means and the fluid conduit means; first gate means, pivotally connected to the second support plate for pivotal movement between a first position and a second position, the first gate means preventing flow of joint compound through the second orifice means when in the first position and allowing flow of joint compound through the second orifice means when in the second position; second biasing means for yieldably urging the first gate means to the first position; third orifice means, formed in the second support plate remote from the first support plate, for overcoating the second layer of the joint compound with a third layer of the joint compound, the third orifice means having a width greater than the second orifice means, the third orifice means being centered, widthwise, with respect to the guide means; second passage means, formed in the second support plate, for fluidically connecting the third orifice means and the fluid conduit means; second gate means, pivotally connected to the second support plate for pivotal movement between a first position and a second position, the second gate means preventing flow of joint compound through the third orifice means when in the first position and allowing flow of joint compound through the third orifice means when in the second position; third biasing means for yieldably urging the second gate means to the first position; first resilient wiper means, mounted on the second support plate intermediate the second orifice means and the third orifice means, for spreading and smoothing the second layer of the joint compound; second resilient wiper blade means, mounted on the second support plate on the opposite side of the third orifice means from the first resilient wiper blade means, for spreading and smoothing the third layer of the joint compound. The taping head may further comprise roller means, mounted on the second support plate, for imprinting a surface pattern on the third layer of the joint compound, wherein the imprinted surface pattern preferably matches a surface pattern on the wallboard. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a partially cutaway view of the right hand side of the backpack unit according to the present invention. Fig. 1B is a left hand view of the backpack unit according to the present invention. Fig. 2 is a partially exploded view of the backpack unit showing the pumping mechanism. Fig. 3 illustrates a section of the handle according to the present invention. Fig. 4 illustrates another section of the handle according to the present invention. Fig.5 is a perspective view of a portion of the handle section illustrated in Fig.3. Fig.6 is a perspective view of a portion of the handle section illustrated in Fig.4. Fig.7 is a partially exploded view of certain elements of the handle section illustrated in Fig.4. Fig.8 is a bottom view of the taping head unit. Fig.9 is a partially cutaway view of the taping head unit. Fig.10 is a perspective view of the underside of an alternative taping head unit. Fig.11 is an illustration of a completely assembled apparatus Turning now to the drawing figures, Figs. 1A and 1B (a right hand view and a left hand view, respectively) illustrate the backpack portion of the present invention. In particular, the backpack comprises a support frame 1 which is adapted to be fitted with suitable webbing (not shown) so as to allow the backpack to be worn on the back of an operator. A container support 3 is attached to the support frame by brackets 5 which may be screwed to or welded to support frame 1 and container support 3. Container support 3 comprises an upper section 7 in the form of a box open at its top which is receivable of a unit container 11 of joint compound. The container support also comprises a lower section 9 which contains pumps 13 and 15 and related equipment, as will be described hereinafter. The unit container 11 is fitted with a pair of grommets 17 and 19 which define puncturable portions of the bottom wall of the container 11. When the container 11 is placed within the upper section 7, a pair of upstanding pipe portions 21 and 23, which are cut at an angle so as to form a "sharpened" edge, are aligned with the grommets 17 and 19, respectively, and insertion of the container 11 fully into the upper section 7 causes these upstanding pipe sections 21 and 23 to pierce the wall of the container and provide fluid communication between the container and the pumps as will be described hereinafter. As may best be seen in Fig. 2, pipe section 21 is connected through elbow 25 and pipe 27 to the inlet 29 of pump 15. Likewise, pipe 23 is connected through elbow 31 and pipe 33 to the inlet 35 of pump 13. In turn, the outlet 37 of pump 15 is connected via elbow 39 and pipe 41 to outlet fitting 43. Likewise, the outlet 45 of pump 13 is connected via pipe 47, elbow 49 and pipe 51 to the outlet fitting 43. The outlet fitting 43 and/or the pipes 41 and 51 may be supported by a bracket 53 mounted on the support frame 1. The outlet fitting 43 is detachably connectable to an inlet fitting 55 of flexible hose 57. Pumps 13 and 15, which are preferably positive displacement pumps, and most preferably rotary flexible impeller (vane) pumps, are driven by motors 59 and 61, respectively. Motors 59 and 61 are preferably electric motors driven by a switch electrical supply, such as a mains electricity supply or a battery, for example a rechargeable battery. Joint compound which is pumped from unit container 11, via pumps 13 and 15, to flexible hose 57 is passed to the handle assembly. The handle assembly comprises a control section 65 (as shown in Fig. 3) and a delivery section 67 (as shown in Fig. 4). The control section 65 comprises a handgrip 69 and a tape supply element 71. A fluid passageway 73 (as shown in dotted lines in Fig. 3) passes through the control section 65 from a socket 75, where flexible hose 57 is fluidically connected to the fluid passage 73, to a socket 77 wherein a plug 79 of the delivery section 67 may be received so as to fluidically connect with the delivery section 67. The handgrip 69 is fitted with switches (in the form of buttons 81-86) for operation of the various functions of the apparatus, as will be disclosed hereinafter. The handgrip 69 is also fitted with a socket 87 for electrical connection of the switches to the various electrical elements in the backpack unit. Additionally, the handgrip 69 is also fitted with an additional socket (not shown) for connection (via a cable connection) to the various electrical devices in the delivery section 67. The tape supply element 71 is shaped substantially as a hollow rectangle (as best seen in Fig. 5) and comprises first and second cross members, 89 and 91, and first and second connecting members 93 and 95. A first disc 97 is rotatably mounted on connecting member 93. A second disc 99 is rotatably mounted on connecting member 95. The mounting of discs 97 and 99 is such that the discs are rotatably mounted substantially coaxially. Disc 97 is provided with a radially extending flange 101 and disc 99 is provided with a radially extending flange 103. At least one of the discs 97 and 99 is moveable axially with respect to the other disc by being supported for rotation on a pin 105 or 107, respectively, received within a corresponding bore 109 or 111 formed in cross member 93 or 95. A spring (not shown) may be fitted in bore 109 and/or 111 so as to yieldably urge at least one of discs 97 and 99 axially toward the other disc. The discs are of such a diameter as to be received within the core of a roll of wallboard tape, whereby a roll of wallboard tape may be supported on the discs for rotation so as to supply tape through the delivery section 67 of the handle. The delivery section 67 substantially comprises a fluid conduit assembly 113 and a support plate 115. The fluid conduit assembly, as best seen in Fig. 7, comprises the plug 79 which is fluidically connected to a chamber 117 which in turn is connected to three fluid supply pipes 119, 121 and 123. Pipe 121 is fluidically connected to supply nozzle 125 and pipe 123 is fluidically connected to supply nozzle 127. Pipe 119 is fluidically connected via elbow 129, pipe 131 and valve 133 to tape supply nozzle 135, which when assembled is disposed in region 137 of the support plate 115. A first stepping motor 139 is mounted on chamber 117 and connected via flexible drive cable 141 to a first bevel gear 143. First bevel gear 143 mates with a second bevel gear 145 which is mounted for rotation with a first shaft 147, shaft 147 having a screw thread formed on the outer periphery thereof. A slider 149 is slidably mounted on rails 151 and 153 with a knife edge (not shown) depending in the gap between rails 151 and 153. Connection member 155 is connected to slider 149 and is fitted with a screw threaded bore corresponding to the screw thread formed on the outer periphery of the first shaft 147, whereby rotation of the first shaft will cause movement of the slider 149 along rails 151 and 153, thereby drawing the knife edge across plate 115. Reversal of the rotation of the first shaft 147 by reversal of the rotation of the first stepping motor 139 will draw the slider, and hence the knife edge, back across plate 115. By alternating the direction of rotation of first stepping motor 139, the knife edge may be drawn back and forth across plate 115 as needed. A second stepping motor 157 is also mounted on chamber 117 and is connected via flexible drive cable 159 to gear box 161. Gear box 161, in turn, contains gears to drive second shaft 163 upon which friction rollers 165, 167 are mounted for rotation therewith. Plate 115 is fitted with guide rails 169 and 171 so as to guide wallboard tape beneath rollers 165 and 167, beneath rails 151 and 153 as well as shaft 147 and over tape supply nozzle 135. In operation, a tape passing between guide rails 169 and 171 on plate 115 may be advanced a predetermined amount by actuation of stepping motor 157 so as to cause a predetermined rotation of shaft 163 and the friction rollers 165 and 167 mounted thereon. Likewise, the tape may be cut by actuation of the stepping motor 139 and the concomitant rotation of shaft 147 causing slider 149 (which is fitted with a knife edge) to slide across the width of the tape on plate 115. In this regard, for example, switch 81 on handgrip 69 can actuate stepping motor 157 so as to cause the tape to advance in a predetermined amount. Likewise, switch 84 can be connected to stepping motor 139 so as to cause movement of slider 149 across the tape. It should be noted, however, that switch 84 alternatively changes the polarity of electrical current fed to stepping motor 139 so as to alternately draw the slider across and then back across the plate 115. As the tape passes over tape supply nozzle 135 joint compound is applied to the lower face 173 of the tape 175. Turning now to Figs. 8 and 9, a second plate 177 is releasably attachable to the delivery section 67 of the handle. In this regard, as may best be seen in Fig. 9, supply nozzles 125 and 127 may be respectively received in passages 179 and 181 in a snap-fit or force-fit manner. Passage 179 communicates with an orifice 183 formed in plate 177. The orifice 183 is fitted with a gate 185 which is pivotally mounted on plate 177 so as to be moveable from a first position in which fluid passage through the orifice is prevented to a second position (as shown in Fig. 9) wherein fluid passage through orifice 183 is permitted. The gate may be biased, by a torsion spring 187, so as to be yieldably urged to the first position. In a similar manner, passage 181 communicates with an orifice 189 formed in plate 177. Orifice 189 is also fitted with a gate 191 pivotally connected to plate 177 so as to be moveable from a first position in which fluid flow through the orifice is prevented and a second position in which fluid flow through the orifice is permitted. Gate 191 may also be biased, as by torsion spring 193, so as to yieldably urge the gate to the first position. Rollers 195, 197 and 199 may be supported on a shaft 201 which in turn is journaled in a support member 203 carried in bore 205 formed in the plate 177. A biasing spring 207 yieldably urges the rollers downwardly so as to force the lower side 173 of tape 175 into contact with wallboard 209. A first resilient wiper blade 211 adjustably mounted in the plate 177 as by a screw support 213 smoothes and spreads joint compound delivered through the orifice 183. A second flexible wiper blade 215 adjustably mounted in plate 177 as by screw support 217 moves and spreads the joint compound delivered to the wallboard through orifice 189. A printing roller 219 may be provided with a surface pattern matching the surface pattern of the wallboard 209 so as to aid in disguising the position of the seams formed by the present apparatus. The roller 219 may be supported by support 221 which in turn is pivotally attached to plate 177 and may be biased into contact with the seam surface as by a torsion spring 223. As shown in Fig. 10, the second support plate may also be formed in other configurations so as to allow specialized taping operations, e.g. the taping of inside corners. In this regard, the plate is formed in two sections 177A and 177B which are at right angles to one another. A pair of printing rollers 219A and 219B is also provided, each of the rollers being disposed so as to imprint one side of the seam. Likewise, a pair of rollers 195A and 195B are also provided so as to bias the tape into contact with the respective sides of the seam. A pair of orifices 183A and 183B are provided so as to place a first coat of joint compound on the upper surface of the tape and these orifices are controlled in a manner similar to the flat taping head shown in Figs. 8 and 9 by the provision of gates 185A and 185B. Likewise, a pair of second orifices 189A and 189B are also provided so as to place a second coat of joint compound on the tape. Although not shown in Fig. 10, a pair of gates analogous to gate 191 in the flat taping head may also be provided to control the flow of joint compound through orifice 189A and orifice 189B. A first wiper 211' and a second wiper 215' are also provided so as to spread and smooth the respective coats of joint compound. In operation, the operator will turn on the apparatus as by the depression of switch 82 which causes power to be supplied to motor 59 which drives pump 13. However, the pressure developed by pump 13 is insufficient by itself to overcome the biasing action of springs 187 and 193 in maintaining gates 185 and 191 in the closed position. However, joint compound will be supplied through tape supply nozzle 135 to the underside of the wallboard tape. Immediately upon turning on the apparatus, the operator will then activate the wallboard tape advance so as to cause the coating of the bottom portion of a predetermined length of wallboard tape which will then be placed into contact with the wallboard 209 by pressure from rollers 195, 197 and 199. The wallboard tape which is so pressed against the wallboard is effectively adhesively adhered to the wallboard and the operator may now move the taping head downwardly (or upwardly) along the wall so as to draw tape from the tape supply wheel (the rollers 165 and 167 permitting such passage of the tape slidingly thereover). With the beginning of motion of the taping head across the wall, the operator may then activate motor 61 driving pump 15 so as to overcome the bias of springs 187 and 198 holding gates 185 and 191 shut. By controlling the operation of pump 15, the operator may control the amount of joint compound being fed to the head so as to suit the particular application conditions being dealt with. When the operator comes to the end of the stroke, the knife edge carried on slider 149 may be activated so as to cut the tape off and allow the operator to finish the end of the tape. This cycle may then be repeated in taping the next seam in the operation. In the case where the operator is merely patching nail or screw holes in the wallboard, e.g. or in those situations where no tape feed is desired, the valve 133 may be closed so as to prevent the feed of joint compound through tape supply nozzle 135 and joint compound may be fed exclusively through orifice 183 and orifice 189. In order to effectuate the process and apparatus of the present invention, it is necessary to utilize a fast-drying joint compound so as to allow multiple coats to be disposed one upon the other in a substantially simultaneous manner. In this regard, Applicant has developed a joint compound comprising about 45% by weight of calcium sulfate, about 35% by weight of a room temperature, evaporable alcohol, about 10% by weight of polyvinyl alcohol, about 5% by weight of polyvinyl acetate, about 3% by weight talc, and about 2% by weight mica. By room temperature evaporable alcohol is meant an alcohol which will readily evaporate under conventional room temperatures in the building trades. Methyl, ethyl and propyl alcohols having been found suitable for this use. Preferably, the alcohol comprises commercially denatured ethyl alcohol. As previously noted, the present apparatus allows for the taping of joints between pieces of wallboard by the substantially simultaneous steps of (a) applying a first layer of a joint compound to the joint between pieces of wallboard, the first layer of joint compound having a first predetermined width, the first layer of the joint compound being substantially centered, widthwise, on the joint; (b) embedding a wallboard tape in the first layer of the joint compound, the wallboard tape having a width substantially equal to the first predetermined width, the wallboard tape being substantially centered, widthwise, on the joint; and (c) overcoating of the embedded wallboard tape with at least one additional layer of the joint compound, the at least one additional layer of joint compound having a width greater than the first predetermined width, the at least one additional layer of the joint compound being substantially centered, widthwise, on the joint.

Claims: Apparatus for taping joints between pieces of wallboard comprising a taping head (115, 177), slidingly contactable with a wall, adapted to apply joint compound and wallboard tape to a joint between pieces of wallboard; a handle (65, 67), connectable to said taping head, adapted to support said taping head, said handle being manually graspable by an operator, said handle having a fluid conduit (73, 113) formed therein adapted to pass joint compound to said taping head; a tape supply (71), mounted on said handle adapted to supply wallboard tape to said taping head; a backpack (1,3), wearable by said operator, adapted to support a supply of said joint compound and to produce a pressurized stream of said joint compound; a flexible connector (57) adapted to fluidically interconnect said backpack and said fluid conduit to pass said pressurized stream of said joint compound from said backpack to said fluid conduit; said apparatus characterized in that said taping head is adapted to substantially simultaneously apply a first layer of a joint compound to a joint between pieces of wallboard, embed a wallboard tape in said first layer of said joint compound and overcoat said embedded wallboard tape with at least a second layer of said joint, said taping head comprising a first support plate (115) attached to said handle, a guide (169, 171), attached to said first support plate, adapted to guide a wallboard tape of predetermined width while being applied to a joint, a first orifice (135), attached to said first support plate, adapted to feed a first layer of joint compound to a surface of said wallboard tape intermediate said joint and said wallboard tape, said first orifice fluidically connected to said fluid conduit, a second support plate (177) releasably attachable to said handle, biasing means (195, 197, 199), attached to said second support plate, adapted to yieldably urge said wallboard tape and, hence, said first layer of joint compound, into contact with said wall, when said taping head is in contact with said wall, to embed said wallboard tape in said first layer of joint compound, a second orifice (183), formed in said second support plate proximate said first support plate, adapted to feed a second layer of joint compound atop said wallboard tape to overcoat said wallboard tape with said second layer of said joint compound, said second orifice having a width greater than said wallboard tape, said second orifice being centered, widthwise, with respect to said guide, a first passage (179), formed in said second support plate, adapted to fluidically connect said second orifice and said fluid conduit, a first gate (185), pivotally connected to said second support plate for pivotal movement between a first position and a second position, said first gate preventing flow of joint compound through said second orifice when in said first position and allowing flow of joint compound through said second orifice when in said second position, second biasing means (187) adapted to yieldably urge said first gate means to said first position. Apparatus according to claim 1, wherein said taping head further comprises a third orifice (189), formed in said second support plate remote from said first support plate, adapted to feed a third layer of joint compound atop said second layer of joint compound to overcoat said second layer of said joint compound with a third layer of said joint compound, said third orifice having a width greater than said second orifice, said third orifice being centered, widthwise, with respect to said guide, a second passage (181), formed in said second support plate, for fluidically connecting said third orifice and said fluid conduit, a second gate (191), pivotally connected to said second support plate for pivotal movement between a first position and a second position, said second gate preventing flow of joint compound through said third orifice when in said first position and allowing flow of joint compound through said third orifice when in said second position, a third biasing means (193) adapted to yieldably urge said second gate to said first position. Apparatus according to claim 2, wherein said taping head further comprises a first resilient wiper blade (211), mounted on said second support plate intermediate said second orifice and said third orifice, adapted to spread and smooth said second layer of joint compound a second resilient wiper blade (215), mounted on said second support plate on the opposite side of said third orifice from said first resilient wiper blade, adapted to spread and smooth said third layer of said joint compound. Apparatus according to claim 2, wherein said taping head further comprises a tape cutter (149), mounted on said first support plate, adapted to cut said wallboard tape widthwise after having passed through said guide. Apparatus according to claim 1, 2, 3 or 4, wherein said taping head further comprises a roller (219) mounted on said second support plate, adapted to imprint a surface pattern on said third layer of said joint compound. Apparatus according to claim 6, wherein said surface pattern imprinted on said third layer of said joint compound matches a surface pattern on said wallboard. Apparatus according to any one of claims 1 to 4, wherein said taping head further comprises a taps advance (165, 167), mounted on said first support plate, adapted to advance a predetermined length of said wallboard tape through said guide means. Apparatus according to any one of claims 1, 2, 3, 4 or 7 claims, wherein said tape supply comprises: a first disc (97) rotatably mounted on said handle, said first disc having a radially extending flange (101); a second disc (99) rotatably mounted on said handle, said second disc having a radially extending flange (103); said first and second discs being rotatable about a common axis and movable on said axis relative to one another; said first and second discs being receivable within a core supporting a roll of wallboard tape; biasing means adapted to cause at least one of said first and second discs to yieldably move toward the other. Apparatus according to any one of claims 1, 2, 3, 4, 7 or 8, wherein said backpack comprises: a support frame (1); a container support (3) mounted on said support frame, said container support being receivable of a unit container (11) of said joint compound in a predetermined orientation; pump means (13, 15), mounted on said support frame, adapted to produce a pressurized stream of said joint compound; power supply means (59, 61), mounted on said support frame, adapted to drive said pump means; piping means (21, 23, 25, 31, 27, 33) adapted to supply joint compound from a unit container mounted in said container support to said pump means; outlet means (39, 49, 41, 51) adapted to fluidically receive said pressurized stream of said joint compound from said pump means, said outlet means including connection means (43) for releasably connecting said outlet means to said flexible connecting means. Apparatus according to claim 9, wherein said pump means comprises a pair of pumps. Apparatus according to claim 10, wherein said power supply means comprises a pair of electric motors, each of said electric motors driving a respective pump. Apparatus according to claim 11, wherein said power supply means further comprises rechargeable battery means for supplying electric power to said electric motors. Apparatus according to claim 9, wherein said piping means further includes means (21, 23) adapted to pierce a wall of said unit container, when it is received within said container support, to form a hermetic fluidic connection between said container and said pumps. A method for taping joints between pieces of wallboard comprising applying a wallboard tape to tape joints between pieces of wallboard which have had a joint compound applied thereto, said method characterized in that it comprises: substantially simultaneously (a) applying a first layer of a joint compound to a joint between pieces of wallboard, said first layer of said joint compound having a first predetermined width, said first layer of said joint compound being substantially centered, widthwise, on said joint; (b) embedding a wallboard tape in said first layer of said joint compound, said wallboard tape having a width substantially equal to said first predetermined width, said wallboard tape being substantially centered, widthwise, on said joint; (c) overcoating said embedded wallboard tape with at least one additional layer of said joint compound, said at least one additional layer of said joint compound having a width greater than said first predetermined width, said at least one additional layer of said joint compound being substantially centered, widthwise, on said joint. The method according to claim 14, further characterized by the step of (d) imprinting a surface pattern on said at least one additional layer of said joint compound. The method according to claim 15, wherein said surface pattern imprinted on said at least one additional layer of said joint compound matches a surface pattern on said wallboard. A method according to claim 14, 15 or 16 wherein said joint compound comprises: about 45% by weight of calcium sulfate, about 35% by weight of a room temperature evaporable alcohol, about 10% by weight of polyvinyl alcohol, about 5% by weight of polyvinyl acetate, about 3% by weight talc, about 2% by weight mica. A joint compound composition to be used with the apparatus of claims 1 to 12 or in the method of claims 14 to 17, comprising 35-60% by weight of a gypsum base plaster; 30-70% by weight of a wetting agent comprising 0-30% by weight of water and an alcohol selected from the group consisting of methyl alcohol, ethyl alcohol and propyl alcohol; and 10-25% by weight of polyvinyl acetate. The composition of claim 18, comprising 0-5% by weight of polyvinyl alcohol. The composition of claim 18, wherein the gypsum base plaster comprises 40-70% by weight of calcium sulfate, up to about 10% by weight of calcium carbonate, up to 5% by weight of silica sand, up to 6% by weight of starch, 0-10% by weight of talc, and 0-10% by weight of mica, and, optionally drying accelerators. The composition of claim 18, wherein the gypsum base plaster comprises 45-60% by weight of calcium sulfate, up to 10% by weight of calcium carbonate, up to 5% by weight of silica sand, up to 6% by weight of starch, 0-10% by weight of talc, and 0-10% by weight of mica. The composition of claim 20 or claim 21, wherein in the gypsum base plaster the talc and mica comprise from 4-20% by weight.

Inventors: RETTI KAHRL, RETTI, KAHRL
Applicants: DRYWALL TECH INC, DRYWALL TECHNOLOGIES, INC.
Application year: 1991
Main classification: E04F21
IPC codes: E04F21