Depending on the scope of the job, you can save yourself some money with DIY drywall repair. Rather than hire a contractor who may charge you an arm and a leg even for a very small patch job, learn how to repair drywall yourself. You will spend a lot less and gain a valuable skill in the process. Drywall that is completely rotted from top to bottom will have to be replaced in full. However, small patches of rotted drywall can simply be cut out and replaced. There are two primary methods for patching. The first involves cutting out the rot and extending the cut to reach studs on either side, and then replacing the piece. Another method is less precise but can save you time. It is known to some pros as a "California patch," but it may have other names. This how-to will explain the first method. Although it will be a little more time consuming, it's good to learn how to do it.
Step 1: Measure the Piece to Cut out
Determine the extent of the rotting drywall and mark around it lightly with a pencil so you know its basic shape. Use your stud finder on either side of the rot to determine where the studs are. You want an exposed stud on either side of the rot to rehang the patch. Once you find the studs, mark them on both sides. Use your level and pencil to draw out a square or rectangle that extends fully around the rot and reaches from stud to stud on center.
Step 2: Cut out Rot
Once accurately marked, score the line with the utility knife. Go over it several times until the blade penetrates the drywall. Don't plunge it too deeply in case there's wiring behind it. When the blade has cut out the section in its entirety, pry out the piece using a drywall knife as a wedge.
Step 3: Measure and Cut Replacement Piece
Measure a shape on the new drywall that's the exact size of the hole. Double check your measurements. Draw the shape with your pencil. Score it along the line with the utility knife and cut it out in the same way you cut the piece out of the wall. Test the fit by inserting it into the hole. Measure anew and recut if it's too big or too small.
Step 4: Hang Replacement Piece
Make sure you know where the studs are before you rehang the piece. Set the replacement in the wall and affix it to the studs with drywall screws placed every 6 to 8 inches on every visible stud. The studs at the end are most important.
Step 5: Tape and Mud
Open up the batch of all purpose Sheetrock brand drywall compound and put some in the trough. With a 4-inch drywall knife, apply the mud along the 4 seams around the replacement, smearing it into the cavities. Lay a length of tape up against the mud along the first side and run the knife over it lengthwise. Repeat this for the other 3 sides. Run the knife over the sides to remove the excess mud.
Step 6: Second and Third Layers
After the first layer is dry, go over each side with another layer of mud, this time using a wider knife. Your goal this time is to cover the tape, although this is not the final layer. After the second layer dries, go over a third time with an even wider knife and another layer of mud. On this pass you want to completely conceal the evidence of a taper. Get the mud as smooth as possible so it blends in with the rest of the wall.
Once the third pass is done, you can add texture to the wall if there is a need. Follow this with a layer of primer. The paint comes last. Don't paint right over the mud, because it will absorb a lot of the hue and make an odd color.