How to Make Simple Knife Cuts to Drywall
In most cases, drywall is cut by scoring through the paper on the finish side (the one with white paper) using a sharp drywall knife.
As soon as you notice the blade dulling, turn it around or replace it. Blades are cheap. Once that side is scored, bending the drywall away from the cut breaks the gypsum core. Cut the brown paper on the back of the board at the break to complete the cut. The cut gypsum is usually ragged, but a pass or two with a drywall rasp cleans it up nicely. There’s no point in cutting drywall precisely—cutting it about ¼-inch short makes it easier to fit, and the gaps will be filled with joint compound. For crosscutting, guide the knife with a 4-foot drywall square to ensure accuracy. To cut along the length, snap a chalk line as a guide.
Making Saw Cuts to Drywall
There are times you’ll have to use a drywall saw. For example, if you need to cut out for a door, you’ll need to make the two vertical cuts with a saw. Then, connect the ends of those cuts with a regular knife cut and snap the piece out. The saw cuts can be made with either a drywall saw that resembles a regular carpenter’s handsaw, or with a wallboard jab saw. If you buy only one saw, make it the jab saw. Tip: It’s easiest and most accurate to hang the drywall before cutting out door and window openings. Use the studs on the side of the opening to guide the saw cuts, and the bottom of the header to guide the knife cut.
How to Cut Out Drywall for Electrical Boxes
It’s important to lay out the location of electrical boxes and rough plumbing carefully.
Draw the cut on the drywall about 1/8-inch larger in all dimensions than the outside of the box. You can skip this step, but for the cleanest cut, score the drywall with a knife. Then, push the jab saw through from the front of the board and cut along the layout lines.
It’s harder than you might think to accurately lay out for cutting electrical boxes. For speed and accuracy, pros make these cuts with a drywall router instead.
Drywall routers are small handheld routers that use 1/8-inch-diameter self-guided bits. The center of the box is marked on the board, and the rough wiring is pushed well back into the box (be sure the circuits are turned off). Then the board is screwed in place with just a few perimeter screws. With the bit set about ½-inch deeper than that drywall thickness, the router is turned on and plunged into the center of the box. The cut is made by cutting to one side until the bit contacts the electrical box, then the bit is carefully hopped over to the outside of the box. Running the router around the box in a counterclockwise direction will cleanly cut it out.
Cuts for doors and windows can also be made with a router. When the router is guided by the inside of the opening, the cut is made in the clockwise direction. Once all the boxes and openings are cut out, the rest of the screws needed to hold the sheet up are driven.
Tools Needed:
Tape measure and pencil Chalk line Drywall knife and blades Wallboard jab saw Drywall square Drywall rasp Drywall saw Drywall router
