There's no exact method for determining how serious a wall crack is without hiring an expert to examine the wall, but you might be able to analyse the crack and surrounding area to determine whether it's likely a surface blemish or a larger problem. Houses usually settle during the first few months and even years after construction, so minor wall cracks are likely. However, gaping cracks, separation, and horizontal crack lines might be signs that the issues are more severe.

How to determine the severity of Cracks

Horizontal Cracks

To determine how serious a wall crack might be, it's best to examine the shape of the crack and the direction it runs on the wall. If the crack is vertical and starts near the apex where the wall and ceiling meet, it might be a sign that it was created when the foundation settled after construction. Vertical cracks run in the same direction as drywall, generally making them less serious. If the crack is horizontal or runs at a jagged 45-degree angle, it might mean there's a more serious problem such as severe foundation shifting or water damage. Surface-blemish cracks can often be repaired with drywall putty, sanding tools, and a fresh coat of paint. More severe cracks usually require professional help to determine the exact cause and might include some reconstruction to prevent further damage.

Stair-Step Cracks

A stair-step crack looks like a flight of stairs and runs in both vertical and horizontal directions across the wall. The continuous pattern usually follows the grout or cement lines between cinder blocks. Stair-step cracks in cinder block foundation walls—usually found in unfinished basements—are a result of soil settling beneath the centre of the wall. The only sure way to tell if the issue is serious is to hire an engineer to perform soil tests and core drill tests to determine what repairs are needed.

Doors and Windows

Another way to test the seriousness of a wall crack is to open and close internal doors to bedrooms and bathrooms, and evaluate whether the doors stick. If so, ensure the sticking isn't a result of paint, faulty hardware or cracked wood. If you determine there's nothing obstructing the swinging motion of the door, it might be a sign of a moderate to severe foundation change, often resulting in wall cracks.

Visible Nails

Study the wall area surrounding the crack and look for nail heads or screw heads that might be visible on the surface of the wall. The nail or screw might not have damaged the drywall, but it has likely pulled away from the wooden stud beneath. This phenomenon is often known as "nail pops" or "nail popping" and might be a sign of structural problems. Nail pops are frequently associated with more serious wall cracks and often signal significant drywall shear movement.

The Fix

Concrete Walls

To repair a concrete wall, you will need an epoxy repair kit. The epoxy will create a watertight seal in the crack. Begin your repair by tapping 3-inch finish nails partially into the crack every 12 inches; these nails will attach injection ports. Epoxy comes in two parts, A and B, which you need to mix just before using. Mix equal parts of the epoxy on a scrap piece of wood with a putty knife. Apply a small amount of mixed epoxy on each injection port tab; attach each port against the wall by covering each of the finish nails with one port.

Spread mixed epoxy over the crack, extending 1 inch on either side of the crack. Cover the flange of each injection port with epoxy as well. You can use a paintbrush dipped in mineral spirits to feather the epoxy at the edges. Allow it to cure for six to 10 hours. Using a caulk gun, inject liquid concrete repair into the ports, starting at the bottom, until the liquid oozes from the port. Plug each port before moving to the next. Allow it to cure for at least five days, then cut the port flush with the wall with a hacksaw.

Fixing Drywalls

Fixing a crack in drywall is the easiest of the three wall types you are likely to encounter in your home. Use a utility knife to cut a 1/8 inch to 1/4 inch V-notch along the length of the crack. Vaccum up loose material. Cover the crack with either mesh joint tape or joint compound and paper tape, followed by a thin layer of joint compound, extending about 2 inches on each side of the tape. Let it dry.

Apply a second coat of joint compound, feathered approximately 6 to 7 inches on either side of the crack. Allow it to dry overnight. Sand lightly until smooth. The wall is ready for paint or wallpaper.

Plaster Wall Patching

Treat minor cracks in plaster similar to a drywall crack, with joint compound. However, if the plaster is pulling away from the lath, you first need to shore up the wall with a two-step process that includes a conditioner spray followed by adhesive.

Start by drilling holes with a 3/16-inch masonry bit that will penetrate the plaster but not the wood lath, every three inches along the length of the crack. Vaccum the dust and debris from the holes. Spray the adhesive conditioner into each hole. Allow dwell time as per the manufacturer's instructions. Inject the adhesive into each hole, beginning at the lowest point of the wall. Clean up excess adhesive with a damp sponge. Immediately attach plaster rings with a drill to pull the plaster tight against the wall. Allow to cure as per the manufacturer's instructions. Remove the plaster rings. Hide the holes and original crack with a coat of joint compound. Lightly sand, then apply a second coat of joint compound. Sand smooth when dry.

Repairing Deep Cracks

If cracks in drywall or plaster are deeper than a 1/4 inch, you will have better success if you first fill the crevices with a filler compound prior to taping with joint compound. Mix the compound as per the manufacturer's instructions. Fill in the crack until it is flush with the existing wall. Cover with tape and joint compound, as outlined previously, to achieve a smooth wall.

Signs of Structural Damage

Concrete walls, especially those in a foundation, are load-bearing walls. Although you can patch minor cracks, major fissures can be a sign of poor structural integrity. A horizontal crack that stretches the length of a wall as well as bulging is a tell-tale sign of serious damage. Cracks of this nature should be repaired only by a professional.