1.  Field of the Invention
The present invention relates in general to a tool for coating both sides of a strip of drywall tape with drywall joint compound, and relates in particular to an applicator head which simultaneously distributes pressurized joint compound directly to an exposed or outer surface of a drywall tape and to an underside or inner surface of a drywall tape as the applicator head is moved over a corner joint. 
2.  Description of Prior Developments
The joints formed between adjoining drywall or wallboard panels are generally covered with a lamination of joint compound and fibrous drywall tape to hide the cracks defined by and between the abutting panels.  Joint compound and tape are typically applied manually by trowel or by a pressurized hand-operated tape and compound applicator to lay down a thin layer of compound and tape over each joint.  The compound is typically applied only to that side of the tape which faces the wallboard panel. 
Once the initial layer or coat of joint compound and tape is applied, it is smoothed over with a tool, such as a roller, and allowed to dry overnight.  A relatively narrow and thin coating of joint compound is subsequently applied over the initial lamination of joint compound and tape using a trowel or a pressurized joint compound applicator.  This second operation covers the exposed or outer side of the drywall tape and sandwiches the tape between the first layer of joint compound and the newly applied layer. 
This second layer of joint compound is then allowed to dry.  After it dries, a third wider layer of joint compound is then applied over the second layer.  Sanding is then required to smooth over the joint. 
Such prior methods are not only time consuming, but are also labor intensive and require considerable skill to achieve a smooth taped joint.  Particular skill is needed to apply tape and compound over a corner joint.  Accordingly, a need exists for a method and apparatus which reduces the time and effort required to form a finished wallboard joint having a wallboard tape sandwiched between two layers of wallboard compound during a single stroke of an applicator. 
A further need exists for a method and apparatus for simultaneously applying wallboard compound to both sides of a wallboard tape as the wallboard tape is pressed against a joint between abutted wallboard panels. 
A further need exists for such a method and apparatus which applies tape and compound to corner joints in a single application requiring no further application of compound to complete the taped joint. 
The aforementioned objects, features and advantages of the invention will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof. 
The present invention has been developed to fulfill the needs noted above and therefore has as an object the provision of a method and apparatus for applying drywall compound to both sides of a wallboard tape as the tape is applied to a wallboard joint. 
Another object of the invention is the provision of a method and apparatus for forming finished wallboard joints in a single step wherein wallboard compound is simultaneously applied to both sides of a wallboard tape as the tape is dispensed through an applicator and over a wallboard joint. 
Yet another object of the invention is to provide such a method and apparatus for applying wallboard tape and compound to a corner joint where wallboard panels meet at substantially right angles. 
These and other objects are achieved with the present invention which is directed to a method and apparatus for applying wallboard compound to front and rear sides of a wallboard tape as the tape is pulled through a taping applicator.  Pressurized wallboard compound is fed to an applicator head through which a length of longitudinally-folded wallboard tape is guided.  As the tape passes through the applicator head, wallboard compound is directed against the outer surface of the wallboard tape as well as around the outer surface of the tape and onto the rear or inner surface of the tape. 
A pair of reservoirs or recesses is formed in the applicator head on both sides of the folded tape to apply a thin layer of joint compound over the tape and beyond the lateral edges of the tape.  In this manner, a layer of joint compound is applied to the joint and laterally beyond the side edges of the tape so as to provide sufficient compound for a seamless laterally-tapered layer of joint compound. 
The aforementioned objects, features and advantages of the invention will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof.