Drywall taping and mudding is the first step of the finishing stage of hanging drywall. Finishing is what you do once all of the drywall is up. Before texture and paint or wallpaper can go onto a wall/ceiling, the drywall requires a minimum of two layers of joint compound. You can apply more layers for a smoother finish if you wish, or you can skim coat the entire surface if you plan on coating the walls with enamel or some type of gloss paint that requires a perfectly smooth surface.
Step 1: Filling Seams
Before the tape can be applied to cover seams, compound must be smeared over them. Seams that should be mudded and taped include any place where two pieces of drywall meet including on the walls and ceiling and in the corners. The long edges of drywall sheets are beveled slightly to provide a little space to absorb compound. Butt joints happen when two ends meet. There is no bevel here, so some pros choose to leave a small gap between butt joints to create space for the first smear of mud.
Step 2: Apply Mud
After preparing the all-purpose compound in the drywall pan, take the 6-inch drywall knife and scoop up a fair amount of it. Starting at one end of the joint, hold the knife nearly perpendicular to the drywall. As you smear the mud into the joint, gradually manipulate the knife so it's almost level with the drywall. This technique spreads the mud out optimally. Scrape any remaining mud off the knife and back into the pan.
Step 3: Tape
Next, position a strip of drywall tape lengthwise over the joint with the joint centered beneath it. Run a continuous length of tape over the entire seam. Make sure the compound holds the tape in place by pressing on it with your hand. Run the 6-inch knife over the tape from center of the joint out to each end. This will flatten the tape and force out any excess mud. Scrape up the excess off the wall and scrape it back into the pan.
Step 4: Second Layer of Mud
Let the tape fully dry on the walls and ceiling. Using the 8-inch drywall knife this time, smear a second layer of mud over all taped joints. Use the same technique to smooth it over the tape. It shouldn't be so thick that you can't see the tape, though. The goal is to gradually widen the path of mud to fully conceal joints while keeping the surfaces as flat as possible. This is the time to cover up the heads of all nails or screws used to fasten the drywall to the studs and joists. With a small amount of compound, scrape over each fastener quickly and confidently. Make sure each head is driven slightly into the drywall before you mud them.
Step 5: Additional Layers
Once the second layer is dry, take the 10-inch knife and smear a third layer over each joint, applying an even wider swath of compound. From there, two optional layers may be added. The first is yet another coat over each joint, while the second is a skim coating of joint compound over all drywall. In both cases, any and all tool marks must be completely covered to achieve the smoothest possible finish.