With this type of tape, an undercoat of spackling is unnecessary. Simply apply the tape over the seam, than add a layer of mud over the tape. Inside corners must be covered with paper tape because the fabric tape will not fold. Again, apply a layer of mud first, covering each side of the corner, then embed the folded tape. Finish smoothing the mud over and around the corner using a special corner knife .
Outside corners require metal corner beads to provide stability and protection to the drywall.
Cut it to fit the full height of the corner with tin snips and fasten it in place with nails or screws every six inches. Then mud over it like any other seam, feathering the spackling out from the corner. This first coat of mud should be completely dry before you go on to the next. A heater with a fan will cut down the drying time considerably. Use a knife blade to scrape off any dried chips at the seams and nail head areas.