Finishing drywall is the second to last step in the actual installation of drywall. Don’t worry, you’re almost there. At this point you’ve already been through the following steps:
Necessary Tools & Materials
• Topping Compound (All-Purpose Joint Compound will suffice)
• 12” Plaster Knife
• 8” Plaster Knife
• Corner Knife
Now you’ve reached the final step in the mudding process, finishing drywall. The finish coat is the most important coat of compound you will put on.
At this point, you should have at least two coats of mud over all of your joints and screw holes. You need to have a fairly flat surface before you begin the finish coat.
First, before applying any compound, check all of the joints for humps. You can do this by placing a 8” wide plaster knife over the joints and rocking back and forth.
If you still get a rocking motion with the knife, you need to go back to the previous step and do more mudding and perhaps a little sanding to “feather out” the joint more.
For the first few coats you were using all-purpose joint compound. For the finishing coat you may want to purchase a “Topping Compound” (also called “Finishing Mud”). This has a slightly finer grain to it and will sand to a smoother finish. It is not required and all-purpose joint compound will work fine.
Prior to beginning your final coat, scrape over all of your seams with your plaster knife to remove any spurs or tiny protrusions in the dried compound. You want to begin with as smooth a surface as possible.
You will be using an 8” plaster knife for the screw holes and a 12” knife for the joints. You will be following the same general steps as on the Mudding Drywall page, shown in the pictures below.
Final Coat Application
Apply a very thin coat of compound to all of your screw holes with an 8” plaster knife. You want to hold the knife at a nearly ninety degree angle to the surface (straight up and down) and apply a fair amount of pressure.
As before, the higher the angle of your knife from the surface, the thinner your application of joint compound will be. You want it to be as thin as possible on this final pass.
Your goal when finishing drywall is not to add more plaster, but to completely smooth out the previous coats.
For the tapered seams and butt joints, use a 12” plaster knife to feather the joints out as much as necessary to smooth out any noticeable “hump” in the plaster.
For butt joints you may need to feather the plaster out 12-14” inches on each side of the joint.
Once the plaster has dried, check all of your joints again with an 8” plaster knife. If any humps still exist, give the surface a light sanding with 150 grit sandpaper and repeat the finish coat.
Once all of your joints are smooth, you are ready to move on to the next step – sanding drywall. Your walls require a final sanding to remove any spurs or ridges before they are ready to prime and paint.
Original Source: How To Drywall