How to Fix Structural Cracks in Walls

Before beginning any repairs, it’s crucial to determine whether the crack is a cosmetic issue or a sign of a deeper structural problem. Here’s how you can assess cracks:

• Hairline cracks (less than 1/16 inch wide): Often occur due to minor settlement, temperature fluctuations, or drying shrinkage in plaster or drywall. These cracks are usually non-structural and can be repaired with simple patching.
• Vertical cracks: If found in foundation walls, these cracks could indicate normal settlement. However, if they continue to widen over time, they may suggest foundation movement.
• Diagonal cracks: Usually found near windows, doors, or corners. Small diagonal cracks may be due to normal settling, but large or widening ones could indicate foundation shifting or structural stress.
• Horizontal cracks: These are the most concerning, especially in foundation walls. They often indicate excessive pressure from soil or water buildup and may require professional intervention.
• Stair-step cracks in brick or masonry walls: These often occur when part of the foundation moves while another remains stable. If they are large, they could be a sign of significant structural problems.
• Cracks wider than 1/4 inch: Large or widening cracks should be monitored closely. If they continue to expand, professional assessment is recommended.

When to Call a Structural Engineer

• If cracks are wider than 1/4 inch or continue to grow over time.
• If doors and windows become misaligned or hard to open/close.
• If you notice multiple cracks appearing at once.
• If horizontal or stair-step cracks are found in foundation walls.
• If water seepage or bulging walls accompany the cracks.

Once you’ve assessed the severity of the crack, the next step is preparing it for repair. Proper preparation ensures that the repair materials adhere correctly and that the problem does not recur.

1. Clean the crack: Use a wire brush or vacuum to remove loose debris, dust, and dirt. A clean surface allows the repair material to bond effectively.
2. Widen the crack (if necessary): For deep cracks, use a chisel and hammer to slightly enlarge the opening. This creates a V-shaped groove, which helps the repair material grip better.
3. Remove loose material: After chiseling, remove any additional debris with a vacuum or compressed air.
4. Dampen the area (for masonry or concrete repairs): Lightly misting the crack with water helps prevent the repair compound from drying too quickly and cracking again.

The right repair material depends on the type of wall and the severity of the crack. Below are the best materials for different situations:

For Concrete Walls

• Epoxy or Polyurethane Injection: Best for deep, non-moving cracks. Epoxy injections restore strength, while polyurethane is flexible and ideal for waterproofing.
• Hydraulic Cement: Expands as it sets, making it great for sealing active leaks in foundation walls.

For Masonry (Brick or Stone) Walls

• Cement-Based Mortar: Suitable for filling deep cracks in brick or block walls.
• Flexible Masonry Sealant: Ideal for smaller cracks that need some flexibility to accommodate movement.

For Drywall or Plaster Walls

• Joint Compound and Mesh Tape: Perfect for repairing small to medium-sized drywall cracks.
• Elastomeric Caulk: Flexible and great for small cracks that may expand or contract.

The application process depends on the type of material you are using.

For Concrete Walls (Epoxy or Polyurethane Injection)

1. Install injection ports along the crack at intervals of 6 to 12 inches.
2. Seal the surface with epoxy paste to prevent leakage during injection.
3. Inject the epoxy or polyurethane starting from the bottom and working upward.
4. Allow the material to cure before removing the injection ports.

For Masonry Walls (Brick, Block, or Stone)

1. Mix a cement-based mortar if using a traditional repair.
2. Apply the mortar into the crack using a pointing trowel.
3. Smooth the surface and mist with water periodically for proper curing.

For Drywall or Plaster Walls

1. Apply joint compound over the crack using a putty knife.
2. Embed fibreglass mesh tape over the compound.
3. Apply multiple layers of compound, sanding between coats for a smooth finish.
4. Prime and paint for a seamless look.

Addressing the underlying cause of the crack is crucial to prevent it from reappearing.

1. Fix foundation issues:
   • If cracks result from foundation settlement, you may need underpinning.
   • Improve grading around your home to direct water away from the foundation.
2. Control moisture:
   • Install proper drainage and downspouts to prevent water buildup near the foundation.
   • Use a dehumidifier in humid areas to minimize expansion/contraction cracks.
3. Reinforce walls (if necessary):
   • For severe foundation cracks, carbon fibre strips or wall anchors can provide additional strength.
4. Regularly inspect for new cracks:
   • Monitor existing cracks and take action if they grow or new ones appear.

• Take photos and measure the width of the crack.
• Check back in a few months to see if the crack has grown.

• Are doors and windows sticking or not closing properly?
• Do you see cracks in interior drywall or ceilings?
• Is your floor uneven or sloping?
• Have you noticed gaps between walls and ceilings?

If multiple signs appear, the foundation may be shifting, and professional assessment is recommended. Contact Mainmark today. 

• Look for water stains or signs of mold near the cracked areas.
• Ensure proper drainage around your home to prevent excessive moisture buildup.
• If water is seeping into cracks, it can lead to further damage.

• If the cracks are large, widening, or accompanied by other structural warning signs, call a foundation expert or structural engineer.
• A professional assessment by a Mainmark expert can determine whether repairs are necessary and what steps should be taken.