This story covers how to finish tapered drywall seams using the three-coat system.
For tapered seams between two drywall sheets, all you need to do is fill the valley. You should build the thickness in three or more coats. You'll sand the final application to create a flat transition.
Resist the urge to excessively mound up the compound in an effort to speed the job. Instead, count on at least three applications. At that point, carefully check your progress by spanning a drywall knife blade across the joint. Look for daylight between the blade and the compound. If the joint's filled, you're ready to sand. If the blade rocks because the compound's too high, be prepared for a lot of sanding.
Project time depends upon your experience level, application care, and size of the room
Mud tray, drywall knife, utility knife
Cutting tape, spreading compound
Compound is mixed and placed into mud pan
Drywall compound, fiberglass mesh tape
Before you start slapping drywall compound on your walls and ceilings, it's helpful to have a clear idea of what you're trying to accomplish with each application. Experienced drywallers produce a smooth surface in three coats, but beginners should prepare themselves for at least four coats.
Drywall compound shrinks as it dries. So even if you achieve a flawless surface off your drywall knife, evaporation will create a depression as the compound dries.
On the first coat, you want to embed the tape at all joints and begin to fill the fastener holes. At outside corners, your goal is to begin a smooth transition from the outside edge onto the surface of the wall.
During the second coat, you'll fill the valley of tapered seams and feather the edges. At butt joints, you'll feather the application outward in both directions from the seam. You'll also widen the application at inside and outside corners. A second coat over fasteners may nearly finish hiding them.
At the third coat, you continue to widen the application at every seam, corner, and over fasteners to create gradual transitions. You'll slightly overfill all areas to compensate for shrinkage and to create a small amount of surplus for sanding to a perfect surface.
Cover the tape with a coat of setting-type or all-purpose compound applied with a 6-inch drywall knife. Lay on enough compound to cover the tape but still permit you to faintly see the texture of the mesh. Avoid the temptation of building a thick coat with this first pass; you'll simply invite cracks as a result of uneven drying.