Ova

How to fix cracks in concrete?

Published in Concrete Repair 6 mins read

Repairing cracks in concrete typically involves cleaning the affected area, selecting an appropriate filler material based on the crack's characteristics, and applying it carefully to restore integrity and appearance.

Understanding Concrete Cracks

Before beginning any repair, it's crucial to assess the type and cause of the crack. Concrete cracks can arise from various factors, including shrinkage during curing, soil settlement, heavy loads, or freeze-thaw cycles. Understanding the crack type helps in choosing the most effective repair method.

Types of Cracks and Their Solutions

Different cracks require different approaches. Below is a guide to common crack types and their recommended repair solutions:

Crack Type Description Recommended Repair
Hairline Cracks Very narrow (less than 1/16 inch), surface-level, often cosmetic. Concrete caulk, latex patching compound, or a thin layer of concrete resurfacer.
Dormant Cracks Stable, showing no signs of widening, narrowing, or movement. Epoxy injection, cementitious patching compounds, or rigid crack fillers.
Active Cracks Cracks that open and close due to temperature changes or shifting. Flexible sealants such as polyurethane caulk or elastomeric fillers designed to accommodate movement.
Structural Cracks Wide (over ¼ inch), deep, or showing significant vertical displacement, often indicating underlying structural issues. Requires professional assessment and specialized repair methods like epoxy injection, rebar installation, or foundation repair.

Step-by-Step Guide to Concrete Crack Repair

For non-structural cracks, many repairs can be a DIY project. Always prioritize safety by wearing appropriate protective gear, such as gloves and eye protection.

1. Assessment and Preparation

Proper preparation is key to a durable repair.

  • Identify the crack type: As discussed above, determine if the crack is hairline, dormant, active, or potentially structural. This dictates your choice of repair material.
  • Clean the crack thoroughly: Use a wire brush, chisel, or stiff broom to remove all loose debris, dirt, dust, and old sealant from within the crack. A shop vacuum can be very effective for removing fine particles. For deeper cracks, consider widening them slightly with a chisel and hammer to create an inverted "V" or "U" shape; this provides better adhesion for the repair material.
  • Ensure the crack is dry: Most repair materials require a dry surface for proper adhesion. Allow adequate drying time, or use a heat gun if necessary, to ensure no moisture remains.

2. Choosing the Right Repair Material

The selection of your repair material is critical for the longevity and effectiveness of the fix.

  • Concrete Caulk/Sealant: Excellent for hairline to moderate non-structural cracks (up to ½ inch wide) in driveways, patios, and sidewalks. It offers flexibility to tolerate minor concrete movement. Look for polyurethane or silicone-based options.
  • Epoxy Crack Fillers: Best for dormant, rigid cracks that require high strength and permanent bonding. They create a strong, durable, and often waterproof seal.
  • Polyurethane Sealants: Similar to caulk but typically used for active cracks or areas needing more flexibility than epoxy. They provide an elastomeric (stretchy) seal that can withstand movement.
  • Cementitious Patching Compounds: Suitable for wider, non-moving cracks or spalled (chipped) areas. These are mortar-based and designed to match the texture of concrete.

3. Applying the Repair Material

The application method varies slightly depending on the chosen material. Here's a common approach, particularly for caulk and sealants:

For Concrete Caulk/Sealant (e.g., Polyurethane or Silicone)

  1. Clean out the crack: As mentioned in the preparation step, ensure the crack is thoroughly cleaned of all loose debris, dirt, and dust.
  2. Install sand or backer rod: For deeper cracks, install sand or a backer rod into the void. This fills the lower portion of the crack, limiting the amount of caulk needed and preventing it from sinking too deep. Push the backer rod down so that there's enough depth remaining for the caulk, typically a maximum of ½-inch from the surface.
  3. Apply the caulk: Using a caulk gun, carefully apply the caulk into the crack. Maintain steady pressure and a consistent bead, ensuring good contact with both sides of the crack. Fill the crack slightly proud (above) the surface.
  4. Smooth out the caulk: Immediately after application, smooth out the caulk using a wet finger, a trowel, or a specialized tooling tool. Dipping your tool or finger in soap and water acts as a lubricant, preventing the caulk from sticking and allowing for a clean, professional finish. Remove any excess material.

For Epoxy or Cementitious Compounds

  • Epoxy Injection: Often requires specialized equipment. Follow manufacturer's instructions for mixing (typically two-part formulas), setting up injection ports, and carefully injecting the epoxy until the crack is filled.
  • Cementitious Patching: Mix the compound according to the manufacturer's directions. Trowel the mixture firmly into the crack, ensuring it's well-compacted. Smooth the surface to match the surrounding concrete.

4. Curing and Finishing

Once the material is applied, proper curing is essential for maximum strength and durability.

  • Allow for full curing: Follow the manufacturer's instructions for curing times. This can range from a few hours to several days, depending on the product and environmental conditions.
  • Protect the repair: Shield the repaired area from foot traffic, vehicle loads, moisture, and extreme temperatures during the curing process.
  • Final touches: Once cured, some repairs may benefit from applying a concrete sealer over the entire slab to enhance durability and provide a uniform appearance.

When to Call a Professional

While many minor cracks are DIY-friendly, certain situations warrant professional expertise:

  • Cracks wider than ¼ inch, or those showing significant vertical displacement (one side is higher than the other).
  • Cracks that are growing rapidly or appear in critical structural elements such as foundations or load-bearing walls.
  • Multiple interconnected cracks forming a "spiderweb" pattern, which could indicate deeper structural issues.
  • If you are unsure about the crack's cause, severity, or the appropriate repair method.

Preventing Future Cracks

Proactive measures can help minimize future concrete cracking:

  • Proper Subgrade Preparation: Ensure the ground beneath the concrete is well-compacted and properly graded before pouring.
  • Control Joints: Install control joints (grooves) in concrete slabs during installation to allow for planned expansion and contraction.
  • Drainage: Maintain proper drainage around concrete slabs to prevent water accumulation and soil erosion beneath the concrete.
  • Avoid Overloading: Do not subject concrete surfaces to loads beyond their design capacity.
  • Sealing: Periodically apply a quality concrete sealer to protect against moisture penetration, freeze-thaw damage, and general wear.