How to Replace Big Gaps of Drywall

Measure the gap with a tape measure and buy drywall of the same thickness, usually 1/2 or 5/8-inch, to fit. Trim the drywall around the gap with a utility knife so all edges around the gap have a wall stud or wall plate exposed for at least half the width (3/4-inch on most walls). Use a long steel straightedge or a framer's square to trim the dry wall evenly.

Replace any missing studs or other interior framing. If the gap results from removal of a big picture window or door, install vertical studs at 16-inch intervals toenailed with framing nails driven diagonally with a hammer to the horizontal framing above and below the gap. Fill a gap with no horizontal framing by building a new wall, with top and bottom plates and interior studs, to fit the gap. Nail that in place to studs on either side.

Cut 4-by-8-foot drywall sheets to the exact dimensions of the gap. Use as many full sheets as possible but cut panels with a utility knife or jigsaw to fit oddly-sized gaps, such as 5 feet wide or 3 feet high. Make certain there is framing on all sides to hold the new drywall panel. Set the panel in place and fasten it with drywall screws on all four corners, then add screws at 18-inch intervals on all studs and surrounding framing. Drive screws with a screw gun until the heads are just below the surface of the drywall.

Fasten self-sticking fiberglass drywall tape over all seams or joints. Press it firmly into the drywall on both sides so it secures tightly. Use a 5-inch drywall knife to spread joint compound over all screw heads and all seams. Press the compound firmly into openings or gaps to fill them completely and smooth the compound with the knife, feathering the edges to the existing surface. Let the compound dry thoroughly.

Sand the dried compound with a power sander and 120-grit sandpaper to smooth it to the drywall surface. Check for any dimples or screw heads that were not fully covered with the first coat. Spread another coat over all screwheads and seams, slightly wider than the first coat. Feather the seams to the surface of the drywall. Let that coat dry and sand again. Add a third coat if necessary to get the seams and screwheads flush with the wall so the surface is smooth and even.