Place a drop cloth along the base of the wall to prevent drips onto the floor. Check the drywall tape for proper placement. Make sure all edges of the tape are flat on the wall with no wrinkles or raised portions. Straighten the tape if necessary. Wipe the tape down with a clean cloth to remove any dust that may interfere with hiding the seams.
Stir ready-mix drywall mud slightly with an electric drill with paddle bit attachment. Use a trowel to place the mud onto a six-inch drywall knife. Apply the drywall mud down the tape with the drywall knife to spread the mud evenly. Press firmly on the knife when applying the mud so that you can fill in the small pores contained in fiberglass tape, and cover the edges of all tape types.
Apply the mud to inside corners by working from the corner outward, spreading the mud beyond the edges of the tape about an inch. Coat one side of the corner using a drywall corner knife and wait for it to dry before coating the second side of the corner. Apply two or three coats of the mud over corner tape to conceal the tape completely, allowing each layer to dry completely between each application. Put on a dust mask and safety goggles to avoid the dust created from sanding the drywall. Sand the layers smooth between applications using a dry sanding sponge. Wait 36 hours for the mud to dry.
Use an eight-inch drywall knife to apply a second layer of mud to the tape. Cover the tape seams and feather out the mud about six inches to either side of the tape. Feather the edges by spreading the mud firmly from the center of the seam out, over the edge onto the drywall creating as thin a coating as possible as you move further from the center, hiding the tape edge. Drag the knife down the tape after feathering to smooth out any high points. Apply a third coat, thinning the mud slightly with water and feathering the mud out to 12 inches. The third coat will completely hide the tape on the drywall, leaving lines of drywall mud instead.
Dip a sanding sponge into a bucket of water then wring it out so that it's damp. Sand the mud with the sponge to remove any high spots and irregularities in the mud over the tape to smooth it out. Allow the mud to dry completely before proceeding with any drywall finish techniques.