If the damaged wall has more than one hole in it, it is better to replace the entire drywall sheet than to replace a section. This will give more structural integrity to the wall, as well as hide any seams.
Check your blueprints to make sure there are no electrical wires running behind the area being cut. If there are, don’t cut too deep with the drywall knife.
For small holes, just use the mud and mesh method instead of cutting out the drywall.
After applying joint compound, use mesh tape versus drywall tape to cover the seams. It is harder to conceal a seam with tape. Plus, mesh creates a stronger bond between the old and existing drywall pieces.
Using a level, measure a straight line across the top and bottom of the damaged section. Then use a drywall knife to cut across those lines, stopping at studs that are past the broken areas. Continue cutting down the drywall adjacent to the studs until the entire section is removed.
If your damaged piece is on a corner wall, try to preserve the drywall covering the corner stud.
There are generally two ways to marry two pieces of drywall together. One way is to bisect the undamaged piece of drywall at the stud, so half the stud is exposed, then butt the undamaged and new drywall together on that stud. However, this takes time and a steady hand. A more time-efficient way is to add a new stud to the existing stud. This method eliminates the need to cut the existing drywall in a straight line and gives the new drywall a stronger anchor. Cut a 2x4 board to size and nail it to the existing stud.
After marrying the new and old studs, measure the hole and cut a corresponding piece of drywall. When cutting drywall, measure out the appropriate length, score the drywall with a box cutter, bend and pop. Then cut the remnants off the back. Place the drywall ends in the center of a stud as it will ensure a strong bond and seamless wall. Use drywall screws about every 8 to 12 inches to attach the drywall to the studs.
If the gap between the existing and new drywall is greater than 1/8 inch, use quick-drying joint compound, also known as mud to fill the gap. Thoroughly mix the drywall compound to the consistency of creamy peanut butter. Cover all the screw dimples and gaps with mud. Then apply mesh across the gaps. The mud and mesh ensures a tight seal between the gaps and creates a seamless and blank canvas for paint. Let the mud and mesh sit for an hour then add a second layer of mud. Let dry completely.