Finishing drywall is the process of applying paper or fiberglass tape over the joints between pieces of installed drywall, then covering the taped seams and filling the screw or nail holes with drywall compound. The process is often known in the building trades as taping and mudding. Part of the taping and mudding process is sanding the dried compound (mud) to smooth the edges, although for very skilled mudders, very little sanding is necessary. When the process is done correctly, the wall surface will be perfectly smooth, and the joints will be invisible to the naked eye, and the finished drywall surface is ready for paint or a textured finish. But taping and mudding can be a frustrating job, so it's important to make sure you understand the process well.
Here are the steps to a perfect drywall finish.
Prepare the Surface
Make sure that all nail or screw heads are driven down below the paper surface of the wallboard. Ideally, the paper surface of the drywall should not be broken (if so, it lessens the holding power of the fastener), but should be recessed just slightly below the surface of the drywall panel. Before mudding, drag a taping knife over the surface to detect fasteners that might not be fully recessed, and if you find any, tighten the screws up or drive the nails just enough to remove the obstacle.
If there any spots with torn paper on the drywall cut them off with a razor or other sharp tool. These will be obstructions to smooth taping and mudding.
Choose Your Tape and Mud
Drywall tape is available in two types: paper and fiberglass mesh As a general rule use paper tape for inside corners, but either will work for flat surfaces. For corners, there are also corner bead products available, which have paper flanges attached to a metal bead. There are both inside corner beads that are mudded into interior corners, as well as outside corner beads that are applied to outside corners, such as the edges on archways.
Joint compound is available in premixed and powdered forms. The premixed all-purpose compound is the best choice for most DIY jobs, though pros may opt for different formulations for different applications.
- Taping compound is the mud used for the main application of tape to the seams and corners, and for the second coat. It is designed to fill in the major gaps.
- Topping compound is used for third finish layer of mud, a skim coat over the seams, and fastener holes that create the final smooth coat. It is not designed to adhere the tape to the drywall panels in the same way that taping compound does.
- All-purpose compound is a general purpose mud that serves all purposes. For most DIYers, this is the only mud they really need.
- Lightweight compound is another all-purpose mud, designed to dry faster. Many pros avoid lightweight compound, believing it has inferior adhesion than the other types.
Whether using powdered drywall compound or a premixed product, give the mud a thorough stirring before using it.
Apply the First Mud Coat
The fiberglass-mesh tape is self-adhesive and can be applied directly to the drywall seams. Paper tape must be embedded in a layer of compound. That makes the taping process a little quicker for the first stage when using fiberglass tape, but the time savings overall is not significant.
When using paper tape, first scoop some mud into a compound tray.
- With a 6-inch taping knife, apply a smooth, thin layer over the joint.
- Immediately press the tape into the mud, centered over the joint.
- Hold the tape in place with one hand while pulling the taping knife over the tape (work from the middle of the joint toward the ends). Apply just enough pressure to squeeze a little compound out from under the tape.
- Immediately apply another thin layer of compound to cover the tape and fill the joint. There should be a very thin layer of compound over the tape at this point, but you will still clearly see the tape through the mud. The edges of drywall panels are slightly recessed as they are manufactured, allowing the paper tape to lay just slightly below the outer surface as it is applied. It will be subsequent layers of mud applied with a wide wallboard knife that raises out the joints so they perfectly flush with the surrounding panel areas.
With fiberglass-mesh tape, the process is a little different.
- Apply a layer of compound thick enough to fill and cover the mesh surface, but again you will still be able to see the fiberglass fibers at this point.
- Smooth the surface and feather the edges as best as you can.
For both paper and fiberglass tape, repeat these steps for each joint.
Finish the inside corners, following the same process. First, apply a thin layer of mud compound, then apply the paper tape or corner bead, then cover the paper with a thin coat of mud. There are special corner drywall knives made for this purpose, but you can also apply compound and cover the tape using a standard 6-inch wallboard knife.
For outside corners covered with metal bead, applying tape is not necessary—just apply mud over each face of the corner with a drywall knife.
With the joints and corners all taped and mudded, apply a small amount of compound over each nail or screw head and smooth the surface. Let the compound dry overnight, or longer if necessary. Clean the tools and put the lid back on the bucket of mud.
Apply the Fill Coat
Lightly sand the dried compound to remove any ridges and bumps. (Wear a dust mask while sanding.) Some craftsman will use a wallboard knife to knock down raised areas of the dried compound before sanding.
Use a 10- or 12-inch knife to spread another layer of compound over the joints, feathering the edges. Once dry, give the surface another light sanding. With this application from a wide knife, the joint areas will now be raised up nearly flush with the faces of the wallboard panels, and the tape should now be hidden under the compound.
Apply the Finish Coat
If you’ve taken care applying and sanding the first coats, the finish coat should require only a very light final application of mud to create a smooth surface. Use the widest drywall knife trowel you have to apply this coat. This knife should be at least 12 inches wide; pros may use even wider drywall knives.
Some pros add a little water to the mud before the final coat (but never more than the equivalent of one pint of water to a five-gallon bucket). If you do this, make sure to mix the water in thoroughly.
Let the compound dry thoroughly, then sand the dried compound. Avoid the temptation to over-sand, as it is easy to sand down into the tape. If the finish doesn't quite meet the smoothness test, don’t be afraid to apply another thin layer.
Wipe the surfaces clean of dust before painting or texturizing the wall or ceiling surfaces.