Learn how to apply tape and joint compound to drywall.
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After the first coat has completely dried, and you have removed any really noticeable imperfections with a pole sander, it is time to apply the second coat of joint compound. For this step, you may find it easier to use a wider drywall knife, because you will be covering the first strip of compound and blending it further across the wall surface. Select a 6" to 12" knife.
You will be building up the drywall joints a little more and then feathering them out smoothly. This step requires a more refined technique than that used to apply the first coat. The joint compound is applied with a little less pressure and a lot more patience. Of the three compound application steps, you will be using the greatest quantity of joint compound. Make sure you have more on hand than during the taping step. In order to achieve a natural-looking feather along the joint, apply more pressure on the outside of the knife and let it ride a little high in the center as you slide it along the seam. If you have applied enough compound correctly, you will not be able to see the joint tape any longer. Be sure to fill and cover all nail and screw holes with joint compound.
The finish coat requires real artistry because you don't want to leave any grooves or streaks after you have finished. The aim is to achieve a base that is as smooth as possible for this final coat. So, before you begin, scrape a wide knife over all the joints to smooth them out a little, which will remove the ridges and tool marks.
Using a 10" drywall knife, apply a second coat of joint compound to each seam. Feather the edges of the joint, and make sure there are no air bubbles in the compound.
Applying the second coat of compound takes more finesse than the first. Using a wider knife and smoothing any imperfections are ways of creating a successful finish.
Start at the center of the seam, pull the joint compound across the seam. Apply pressure to the outside edges of the knife as you pass over the joint. Pass over the joint to feather the compound out. Continue to pass over the joint until the air bubbles are removed.
If you were able to spread smooth, blended layers of joint compound during the previous two steps, your work during the third coat will be easier. After the second coat is dry, smooth a pole sander across any bumps or humps. You may want to shine a light across the surface to identify the joints that may need extra attention during this third coat.
While some DIYers prefer to use premixed joint compound right out of the bucket, it is possible to add a little water to the premixed bucket during this step. In fact, if you plan to use the paint-roller technique below, you may want to add water to thin the mixture, which will make it easier to smooth the compound onto the wall. Using a paint roller with an extension will also make it easier to apply the third coat to any ceiling joints. You will need a trowel to finish the seam, however, after you apply the compound with the roller.
If you choose to use a drywall knife for this finishing coat, choose a knife that is wider than the one you used during the previous step. A 10" or 12" knife will work perfectly well. The objective of this step is to achieve a smooth feather. The aim is to end up with as few imperfections as possible, because each imperfection will require more work during the sanding step.
Prepare the drywall joint compound to begin with, adding water to the joint compound mix if needed or lightly stirring a premixed tub (Image 1). You can add a little water to a premixed tub to make it easier to spread. Only prepare as much of the compound as you plan to use immediately, because it can dry out.
Using a paint roller and paint tray, spread the joint compound across — and wider than — the previous coat of compound (Image 2).
Use a trowel to smooth the compound for a seamless finish (Image 3).
Excerpted from Do It Yourself Home Improvement
© Dorling Kindersley Limited 2009