The Best Way to Fix Deep Wall Cracks

Remove dust and debris from the edges of the crack, using a taping knife. If there are any loose chunks of wall inside the crack, carefully remove these as well. A screwdriver or other long, skinny object often makes an ideal tool.

Apply a very thin coat of compound with the taping knife, running it directly over the crack. Do not try to force the compound into the crevice, as a thick application will typically not set correctly and may be difficult to smooth out. While you can fix minor ridges with sanding paper, making sure that all of the compound coats are as thin as possible will save you a fair amount of time, and may limit the coats you have to apply. Work with the compound, spreading it out until it is even, using the edge of the taping knife to fade the compound into the rest of the wall.

Cut a piece of drywall tape and lay it flat against the crack, making sure that the entire crevice is covered and the tape is pressed into the wet compound by running the taping knife firmly over it.

Take a small amount of compound and apply it to the tape, making sure that you smooth out the edges so there is no line between the undamaged wall and the compound. Let the compound dry according to the manufacturer's directions.

Sand the area lightly with fine sanding paper. Apply another thin coat of compound, spreading it evenly and smoothing out the edges. Let it dry. Keep repeating this process until the deep crack is repaired. You may need two to three more coats of compound. Make sure to sand the patch lightly between each coat to make sure the finished application is even. After your final coat, sand the area again with fine sanding paper until it is smooth. Run your hand over the area to check for any differences between the patch and the rest of the wall.

Paint the area with primer and allow it to dry. Next, finish fixing the deep wall crack by painting over the patch with paint that matches the rest of the wall. Ideally, you should use a can of paint left over from painting the wall in the first place. If you do not have this available, take a paint chip to your local hardware store and purchase a small can of touch-up paint. If you simply buy the paint based on the name of the color, you run the risk of having a slightly different shade of the same paint, which can make your patching job stand out.