Follow these steps for basic drywall mudding which should be done to cover the seams between drywall sheets and prepare for painting.
Save most of the sanding until before and after the final coat. It’s very easy to quickly remove too much mud with sandpaper.
Instead of sanding, consider wet sand, using a moistened sponge to smooth out the dry mud, or just scrape over it firmly and evenly with a dry 10-inch knife.
Prepare the Mud
Mud can be purchase pre-mixed to spare time, mess, and water. In powder form, mix with an electric mixer with the appropriate amount of water per instructions on the bag or box. Pre-mixed mud should be mixed lightly, but not enough to cause a considerable amount of bubbles in the mud. Fill the mud pan with all-purpose mud when you are ready to begin. Apply enough mud so that there are three inches of mud on either side of every seam.
Apply One Coat Before Taping
Place a generous amount of all-purpose mud onto a 4.5-inch knife. This first coat of mud works as glue to stick the tape to the drywall. Start with horizontal seams first. Hold perpendicular to the wall at a 45-degree angle for best results. Start at one side of the seam and spread the mud along the length of the seam. Work from top to bottom when applying mud to vertical seams; work from one side to another when applying mud to horizontal seams.
Cut and Apply Tape
Cut the tape to the correct length for the entire seam, starting with the horizontal seams firsts. Press the tape gently into the mud with your hands, taking care that it is aligned evenly with the seam. With a clean, slightly dampened 4.5 inch knife, run it firmly over the tape, squeezing out excess mud from behind the tape. Apply enough mud so that there are three inches of mud on either side of every seam.
Allow to Dry and Scrape Smooth
Allow drying for several hours or all day, until the mud lightens in color. Using the 10-inch knife scrape down any mud that makes an uneven surface.
Another Coat of Mud
Using the 6-inch knife apply enough mud over the tape to cover it completely and smoothly. Always go over the applied mud with a wet knife from top to bottom or side to side to smooth out before drying. Allow drying for several hours.
Apply More Coats
At this point, the mud and drywall may appear perfect, but it will continue to shrink the longer it dries. Applying another coat or two before the final coat is recommended. Slowly widen the mud strip with each coat, until it is about 12 inches wide. Feather the edges so that there is no sharp contrast between the drywall and the mud. Use fine-grit sandpaper to smooth out before the final coat, which should be applied with a 10-inch knife using topping mud.
Inside corners should be done similarly to other joints, except a 45-degree corner tool will make your job incredibly easier. Apply mud, then tape, then several more mud coats just as before. Take care to not let the tape sink into the seam.
Outside corners should be covered by a metal corner strip, not tape, which can be nailed or screwed into place. Mud is not required before the metal strip; Top with about 2 coats of mud, enough to cover the metal.
These basic mudding techniques will prepare drywall for a beautiful paint job.