Finding cracks in concrete basement walls is common, but they can lead to bigger problems if left untreated. Even small openings can allow water, insects, and soil gases to enter your home. While some cracks are caused by normal settling, others may point to shifting soil or drainage issues around the foundation.
In this guide, we’ll walk through a proven method for sealing non-structural cracks using epoxy injection, along with practical guidance from Hugo Sanchez, a contractor featured on This Old House. Sanchez shows how this approach fills concrete cracks from the inside out for a longer-lasting repair.
Do Cracks in Walls Indicate a Structural Problem?
Not all cracks in concrete walls are cause for alarm. In many cases, small hairline cracks are simply the result of normal shrinkage as the concrete cures. These are typically cosmetic and don’t affect the home’s structural integrity.
Wider cracks, however, especially those that grow over time or appear alongside shifting soil, can signal foundation movement. Vertical or diagonal cracks are often caused by settling, while horizontal cracks may indicate more serious pressure from soil pushing against the wall.
Even when a crack isn’t structural, it can still create problems. Any opening in a foundation wall can allow water, insects, and even radon gas to enter the basement, leading to moisture damage and poor indoor air quality.
If you notice large, recurring cracks, bowing walls, or signs of ongoing movement, it’s best to consult a structural engineer. These conditions may point to a more serious issue that requires professional evaluation.
Why Epoxy Injection Is Better Than Surface Patching
Traditional masonry patching products, such as hydraulic cement, can fill cracks in concrete walls and stop minor leaks at first. But these materials are rigid, so they don’t flex as the foundation naturally expands and contracts over time.
That lack of movement is where problems start. As the wall shifts with seasonal changes or settling soil, the patch can lose its bond and the crack may reopen. In many cases, homeowners end up repeating the repair after just a few years.
Epoxy injection offers a more durable solution because it addresses the crack at its source. Rather than covering the surface, the epoxy is injected deep into the crack, where it bonds the concrete back together. Once cured, it creates a continuous seal that helps prevent water intrusion and holds up better to minor movement.
For long, narrow cracks in poured concrete walls, especially those that leak during heavy rain, this method provides a longer-lasting repair than surface patching alone.
Before You Start Concrete Repairs
Before injecting epoxy, make sure the crack is clean, dry, and accessible along its full length. Use a wire brush and vacuum to remove any loose concrete, dust, or old filler that could prevent the epoxy from bonding properly.
Moisture is especially important to check. If the crack is damp, the epoxy may not adhere as intended. In some cases, you can dry the area with a heat gun or hair dryer, but if water continues to seep in, it’s best to wait until the wall has fully dried.
It’s also important to plan the repair from bottom to top. Because epoxy is injected in stages, working upward helps ensure the crack fills completely and reduces the risk of trapping air inside the wall.
How To Repair a Basement Wall Crack Using Epoxy Injection
Epoxy injection systems seal cracks by bonding the concrete back together from the inside out. The process involves installing surface ports, sealing the crack, and then injecting epoxy so it fills the entire void.
Step 1: Clean the Crack Thoroughly
Use a wire brush to remove loose concrete, paint, and old filler from the crack. Then vacuum away all dust and debris to ensure a clean bonding surface.
Step 2: Mark Port Locations
Place injection ports along the crack, spacing them about 12 inches apart. These ports will allow you to deliver epoxy evenly along the full length of the crack.
Step 3: Attach the Injection Ports
On the This Old House episode “Stone Cold Pavers,” masonry contractor Hugo Sanchez says that these ports allow low-viscosity epoxy to inject deep into cracks, ensuring the repair penetrates beyond the surface.
Expert Tip: Injection ports are designed to deliver epoxy through the full depth of the crack, not just to seal the wall face.
Step 4: Seal the Surface of the Crack
Mix the two-part epoxy sealer and spread it over the crack, covering the area about 1 inch on either side. Be sure to seal around each port, leaving only the opening exposed.
This surface seal acts as a barrier, allowing pressure to build inside the crack during injection so the epoxy can fully penetrate the void.
Step 5: Inject the Epoxy
Load the epoxy cartridge into a caulk gun and begin injecting at the lowest port. Work slowly and steadily to allow the material to flow deep into the crack.
Although you can’t see the epoxy inside the wall, it travels through the interior of the crack and fills the void behind the surface.
Step 6: Work Up the Wall
Continue injecting epoxy until it begins to appear at the port above. This indicates that the crack has been filled between the two ports.
Pro Tip: Sanchez says that once epoxy reaches the next port, plug the lower one and continue working upward to fully fill the crack.
Repeat this process until the entire crack has been filled.
Step 7: Allow the Epoxy to Cure
Let the epoxy cure fully before removing the ports. This typically takes at least 48 hours, depending on the product and conditions.
Sanchez notes that properly injected epoxy can achieve compressive strengths exceeding those of the original concrete, making it a structural repair rather than just a surface fix.
Step 8: Remove the Ports and Finish the Surface
Once the epoxy has cured, cut off the injection ports with a hacksaw. If desired, apply a thin layer of patching compound over the area for a smoother finish.
When To Call a Pro for Foundation Cracks
Epoxy injection is an effective repair for many non-structural cracks, but it’s not the right solution for every situation.
If you notice cracks that are wider than 1/4 inch, growing over time, or accompanied by bowing walls or uneven floors, the issue may be structural. Horizontal cracks, in particular, can indicate pressure from soil outside the foundation and should be evaluated by a professional.
Recurring water intrusion is another sign that a deeper problem may be at play. Poor drainage, hydrostatic pressure, or foundation movement can reopen cracks, even after they’ve been sealed.
In these cases, a structural engineer or foundation specialist can diagnose the underlying issue and recommend a long-term solution, which may include drainage improvements, wall reinforcement, or exterior waterproofing.
