How to Fix Cracks in Concrete: DIY & Professional Repair Tips Explained

Introduction

Concrete is one of the most durable materials used in Australian homes, from driveways and patios to foundations and garage floors. However, over time, even the toughest concrete can develop cracks due to weather changes, soil movement, heavy loads, or poor installation. Cracks not only affect the appearance of your property but can also signal deeper structural issues if left untreated.

In this complete guide, we’ll walk you through how to fix cracks in concrete, covering both DIY repair methods and professional solutions. You’ll also learn about different types of cracks, causes, repair products, and cost considerations to help you make the best decision for your home.

Whether you’re patching a small crack yourself or considering expert help for larger repairs, this resource will give you all the knowledge you need.

What Causes Cracks in Concrete?

Concrete is one of the most durable and widely used building materials for Australian homes, especially in driveways, patios, and foundations. However, cracks in concrete are almost inevitable over time due to environmental conditions, material behaviour, and external stresses. Understanding what causes concrete cracks helps homeowners not only repair but also prevent them in the future. Below are the most common reasons why cracks form.

Shrinkage Cracks

Shrinkage cracks typically occur as concrete cures and loses moisture. As the water evaporates, the slab contracts, and if it lacks adequate control joints or reinforcement, thin hairline cracks form on the surface. These cracks are usually cosmetic and don’t pose a structural risk. However, they can allow water ingress, which may cause further deterioration, especially in outdoor slabs exposed to rain and garden irrigation. Applying a concrete sealer can minimise shrinkage crack issues.

Settlement Cracks

Settlement cracks are more serious and develop when the soil beneath a concrete slab shifts, compresses, or erodes. In Australia, reactive clay soils are particularly prone to movement due to moisture fluctuations. These cracks are often wider, uneven, and can compromise the slab’s integrity. A professional assessment is usually recommended, as repairing settlement cracks may require underpinning or slab stabilisation techniques rather than just surface patching.

Temperature Changes

Concrete naturally expands in hot weather and contracts in colder conditions. Without proper expansion or control joints, this constant thermal movement puts stress on the slab, eventually leading to cracks. Australian driveways and patios exposed to high summer temperatures are especially vulnerable. Preventative measures include installing joints at the correct spacing and using reinforcement mesh to distribute stress evenly.

Heavy Loads and Traffic

Concrete is strong but not indestructible. Driveways, garage floors, and workshop slabs bear the brunt of heavy vehicles, machinery, and daily wear and tear. When loads exceed the concrete’s design capacity, cracks can develop. Overloading is a common issue for residential driveways where large utes, caravans, or boats are parked. Reinforced concrete with adequate thickness can reduce the likelihood of load-related cracks.

Poor Installation or Materials

Improper installation practices and substandard materials are another leading cause of premature cracking. Using the wrong concrete mix, insufficient reinforcement, or poor finishing techniques weakens the slab from the start. If the base layer isn’t compacted properly or drainage is ignored, the slab may shift or deteriorate quickly. Hiring reputable concreters and ensuring compliance with Australian building standards is essential to long-term durability.

Types of Concrete Cracks and Their Severity

Understanding the different types of cracks in concrete is crucial for deciding whether you can handle the repair yourself or if you should call in a professional. Not all cracks pose the same risk—some are minor surface blemishes, while others may signal structural concerns that need urgent attention. Below are the most common types of cracks homeowners encounter and how severe they typically are.

Hairline Cracks

Hairline cracks are the most common and usually appear as very fine, surface-level lines. They often occur due to normal curing and shrinkage of concrete as it dries and loses moisture. While they may look concerning, they are generally cosmetic and do not affect the structural integrity of the slab. These cracks can often be sealed with DIY concrete fillers or patching compounds to prevent moisture from seeping in and causing further deterioration. For Australian homeowners, particularly in coastal or humid areas, sealing hairline cracks promptly is important to protect against moisture damage and salt exposure.

Vertical or Diagonal Cracks

Vertical or diagonal cracks are more serious because they often indicate underlying soil movement or foundation settlement. These cracks can vary in width, and if they widen over time, it’s a clear sign of shifting beneath the slab. Left untreated, they may compromise the stability of the structure, especially in driveways, garage floors, or home foundations. In such cases, it is best to consult a structural engineer or licensed concreter to assess whether reinforcement, underpinning, or slab replacement is necessary.

Expansion Cracks

Concrete naturally expands in hot weather and contracts when it cools. If proper control joints are not installed during construction, this thermal movement can cause expansion cracks along slab edges or joints. While these cracks are not typically a sign of structural failure, they can widen over time. The good news is that expansion cracks are manageable with flexible sealants or fillers designed to absorb movement. Using high-quality joint sealants helps protect the slab from water ingress and further cracking.

Wide Cracks (>5mm)

When cracks exceed 5 millimetres in width, they often signal more significant issues, such as soil instability, poor sub-base preparation, or heavy load damage. Wide cracks are rarely just cosmetic and usually require professional repair. Attempting to fill them with standard DIY products may provide temporary relief but will not address the root cause. In Australia, where clay soils can swell and shrink dramatically with moisture changes, wide cracks are a common concern for homeowners. Professional solutions may involve epoxy injections, slab jacking, or even partial replacement of the concrete section.

Assessing Whether to DIY or Call a Professional

Before attempting any concrete crack repair, homeowners need to carefully evaluate the damage. While some cracks can be handled with basic DIY kits, others indicate structural or soil-related issues that require professional expertise. Knowing when to tackle it yourself and when to call in help can save time, money, and long-term stress.

Size of the Crack

The width of the crack is often the first and most important indicator. Hairline cracks under 1–2mm wide are typically cosmetic and can be sealed using DIY crack fillers or patching compounds. These are common in driveways, patios, and garage floors. However, once cracks exceed 5mm in width, they may suggest soil movement, heavy loading, or inadequate reinforcement. Larger openings also allow more water infiltration, which can weaken the slab and encourage further damage.

Depth and Spread

Another factor is how deep and extensive the crack is. Surface-level cracks that don’t extend far below the surface are generally safe to repair at home with polyurethane sealants or resurfacing products. On the other hand, deep cracks that run through the slab may compromise structural integrity. In such cases, epoxy injections or slab stitching might be required—techniques best handled by licensed concrete repair professionals.

Location of the Crack

Where the crack appears is just as critical as its size. A small crack in an outdoor path may only be a cosmetic issue, while a crack in a foundation wall, basement floor, or load-bearing slab is a red flag. These locations bear significant weight, and damage here may indicate shifting soil or inadequate support. Attempting DIY in such areas could mask the problem instead of fixing it, leading to expensive future repairs.

Identifying the Cause

Finally, homeowners should consider the underlying cause of the crack. Shrinkage cracks from curing are often harmless, but settlement or movement-related cracks are much more serious. If you cannot determine why the crack appeared, it’s best to consult an expert. Professionals can perform soil testing, structural assessments, and moisture checks to prevent the issue from recurring.

Pro tip for Australian homeowners: If a crack is wider than 5mm or deeper than 10mm, it should always be inspected by a professional. DIY solutions are best for minor surface damage, but bigger structural concerns need expert attention to ensure safety and long-term durability.

DIY Concrete Crack Repair: Step-by-Step Guide

Repairing cracks in concrete yourself can save time and money if the damage is minor and non-structural. By using the right tools, materials, and techniques, you can restore your driveway, patio, or slab while preventing water intrusion and further deterioration. Below is a step-by-step concrete crack repair guide tailored for homeowners.

Tools and Materials Needed

Before starting the repair, gather the essential tools and products:

• Wire brush – to scrub away dirt and loose concrete.
• Chisel and hammer – for widening cracks when necessary.
• Shop vacuum or air blower – to remove dust and debris.
• Concrete crack filler (epoxy, polyurethane, or liquid filler for hairline cracks).
• Trowel or putty knife – for spreading and smoothing filler.
• Caulking gun – if using tube-based sealants.
• Safety gear – gloves, goggles, and a dust mask to protect yourself during chiseling and filling.

Step 1 – Clean the Crack

A proper repair begins with a clean surface.

1. Use a wire brush to scrub away dirt, algae, and loose fragments inside the crack.
2. For stubborn debris, chip away lightly with a chisel.
3. Remove dust and particles using a shop vacuum or compressed air blower.

Why this matters: Dust and debris prevent the filler from bonding properly, leading to premature cracking or failure.

Step 2 – Widen the Crack (If Needed)

Hairline cracks are often too narrow for filler to penetrate deeply. Widening helps improve adhesion.

1. Hold a chisel at a 45-degree angle and gently chip along the crack edges.
2. Aim for a “V-shaped groove” so the filler can lock into place.
3. Avoid over-chiseling – you only need to make the gap wide enough for the sealant.

Pro tip: For cracks larger than 3–5mm, widening is usually not necessary.

Step 3 – Apply Concrete Filler

Now it’s time to fill the crack using the appropriate product:

• For hairline cracks (<3mm): Use a liquid filler or patching compound that seeps into fine lines.
• For wider cracks (>3mm): Use epoxy or polyurethane sealant, which offers strong bonding and flexibility.

Application method:

1. Insert a caulking gun nozzle into the crack and slowly squeeze filler inside.
2. For small surface cracks, pour liquid filler directly into the groove.
3. Ensure the filler reaches the full depth, not just the surface.

Why epoxy/polyurethane? Epoxy provides structural strength, while polyurethane is flexible and resists expansion/contraction from temperature changes.

Step 4 – Smooth and Seal

Once the filler is applied, smooth the surface:

1. Use a trowel or putty knife to level the filler with the surrounding concrete.
2. Feather the edges so the repair blends seamlessly with the slab.
3. For exterior slabs, consider applying a concrete sealer after curing to protect against moisture, salt, and weathering.

Step 5 – Allow Proper Curing

Curing time is crucial for long-lasting repairs.

• Follow the manufacturer’s instructions (curing may range from 2 hours to 48 hours).
• Protect the repaired area from foot or vehicle traffic until fully hardened.
• In outdoor areas, shield the crack from rain or direct sun with a tarp while curing.

Pro tip: Applying too much filler at once can cause shrinkage or cracking. Always layer for deeper repairs.

✅ Final Word: By following these DIY crack repair steps, you can restore small to medium-sized concrete cracks effectively. However, if cracks are wider than 5mm or show signs of structural damage, consulting a professional is the safest option.

DIY Fixes for Specific Areas

Not all concrete cracks are the same, and where the damage occurs often determines the best repair method. Driveways, garage floors, and patios each face unique stressors—such as heavy vehicle weight, exposure to oil and chemicals, or constant weather changes. Below is a detailed guide on how to tackle cracks in these specific areas.

Fixing Cracks in Driveways

Driveways endure the most wear and tear because of constant traffic, heavy loads, and exposure to rain and heat. To repair cracks effectively:

1. Thorough cleaning – Use a pressure washer or stiff wire brush to remove loose concrete, dirt, weeds, and oil stains. A clean base is critical for filler adhesion.
2. Filling with durable products – Opt for epoxy-based fillers or polymer-modified repair compounds. These are designed for strength and resist crumbling under vehicle weight.
3. Sealing the surface – After the filler cures, apply a concrete sealer across the repaired area or the whole driveway. This prevents water seepage, which can cause the crack to reopen during Australia’s wet and dry seasonal cycles.

Pro tip: For cracks larger than 10mm, consider saw-cutting and patching with fresh concrete for a long-lasting solution.

Fixing Cracks in Garage Floors

Garage floors experience a different set of challenges, including oil spills, chemical exposure, and occasional heavy impacts from tools or machinery. Here’s how to fix cracks in this setting:

1. Preparation – Sweep and vacuum the crack thoroughly. For deep cracks, use a chisel to slightly widen the space for better filler penetration.
2. Choosing the right filler – Polyurethane-based fillers are ideal since they resist oils, fuels, and chemicals better than standard epoxy.
3. Application – Fill the crack carefully, slightly overfilling, then level with a trowel or putty knife. Smooth out the surface so it blends seamlessly with the surrounding slab.

Pro tip: Once repairs are done, consider applying an epoxy coating across the garage floor. It not only hides old cracks but also protects against future damage.

Fixing Cracks in Patios or Outdoor Slabs

Patios and outdoor slabs face constant weather exposure—harsh sunlight, heavy rain, and natural ground movement. Cracks here need flexible repairs:

1. Flexible fillers – Use products specifically designed for outdoor use, such as polyurethane sealants that expand and contract with temperature changes.
2. Resurfacing option – If the patio has multiple cracks or an uneven look, applying a resurfacing compound over the entire slab can restore a fresh, uniform finish.
3. Sealing for longevity – A quality sealer helps repel water, prevents staining, and reduces the chance of new cracks forming.

Pro tip: Add a slip-resistant sealer to patios for safety in wet conditions.

Professional Concrete Crack Repair Options

While DIY methods work for minor surface cracks, more severe or structural damage often requires professional repair. Experts use specialized techniques and equipment to restore strength, prevent further deterioration, and improve the concrete’s lifespan. Here are the most common professional options:

Epoxy Injection

Epoxy injection is ideal for structural cracks that compromise the stability of concrete. Professionals inject a high-strength epoxy resin into the crack under pressure, filling deep voids and bonding the concrete back together. This method restores the structural integrity of foundations, walls, and slabs while preventing moisture infiltration.

Polyurethane Foam Injection

Polyurethane foam is highly flexible and expands when injected, making it suitable for cracks exposed to moisture or movement. The foam fills gaps and creates a watertight seal while allowing the concrete to adjust to thermal expansion and contraction. It’s a preferred solution for basements, driveways, and areas prone to water exposure.

Slab Jacking or Mudjacking

When cracks are caused by uneven or sunken slabs, professionals may use slab jacking (also called mudjacking). A grout mixture or polyurethane foam is injected beneath the slab, lifting and leveling the surface back into place. This technique is commonly used for driveways, sidewalks, and garage floors, restoring both function and appearance without complete slab replacement.

Concrete Resurfacing

For widespread cracks and surface damage, contractors may recommend resurfacing. This process involves applying a thin overlay of cement-based material to the slab’s surface, creating a smooth, uniform finish. Resurfacing not only hides cracks but also enhances durability and improves the overall aesthetics of patios, driveways, or walkways.

Costs of Concrete Crack Repair in Australia

Repairing cracks in concrete can vary widely in cost depending on whether you take the DIY route or hire professionals. Small hairline cracks are inexpensive to repair using DIY fillers, while larger structural issues often require expert intervention. On average, homeowners in Australia can expect DIY kits to cost between $20–$100, whereas professional services such as crack injections or slab jacking can run into the hundreds or even thousands. Factors like location, crack severity, accessibility, and whether the repair is cosmetic or structural also play a significant role in final costs.

Concrete Crack Repair Costs in Australia

Preventing Future Cracks in Concrete

Preventing cracks is always more cost-effective than repairing them later. One of the most effective strategies is sealing your concrete regularly. A quality sealer protects against moisture penetration, chemical spills, and freeze-thaw cycles that can weaken the surface over time. Just as important is ensuring proper drainage around your home, since water pooling near slabs or foundations can cause soil movement and eventual cracking. Avoid placing heavy loads or overloading driveways, garage slabs, or patios, as excess weight can stress the surface. Incorporating control joints during installation also allows natural expansion and contraction without damaging the slab. Finally, don’t overlook landscaping—tree roots and shifting soil are common causes of cracks. Properly maintaining garden beds and avoiding large trees too close to foundations will help reduce these risks. By combining sealing, drainage, load management, and soil care, homeowners can significantly extend the life of their concrete surfaces.

Eco-Friendly and Long-Term Solutions

Homeowners can now protect their concrete while also caring for the environment by choosing eco-friendly repair and maintenance methods. A simple step is to opt for low-VOC concrete sealants, which provide strong protection against moisture and weathering without releasing harmful chemicals into the air. For resurfacing projects, recycled concrete materials are a sustainable option, reducing waste and lowering the demand for new raw materials. In driveways and outdoor spaces, permeable concrete is another long-term solution, allowing rainwater to pass through and reducing issues like pooling, erosion, and slab damage. For structural or wider cracks, professional eco-friendly fillers available in Australia can restore integrity while minimising environmental impact. By combining these practices, homeowners not only extend the lifespan of their concrete surfaces but also contribute to a more sustainable future—achieving durability, safety, and environmental responsibility in one approach.

Common Mistakes to Avoid in DIY Concrete Repair

While DIY concrete repair can save money, homeowners often make mistakes that compromise the results. One common error is failing to clean cracks thoroughly before applying filler—dirt, dust, and moisture prevent materials from bonding properly. Another issue is using the wrong type of filler; for instance, flexible sealants are suited to driveways and outdoor areas, while rigid fillers are better for indoor slabs. Many also ignore underlying soil or drainage problems, which leads to recurring cracks even after patching. Overfilling cracks without smoothing the surface can cause unsightly bumps and uneven finishes. Finally, attempting to repair structural cracks—those wider than 5mm or affecting foundations—without professional input can worsen the problem and create safety risks. By avoiding these mistakes and recognising when expert help is needed, Australian homeowners can achieve durable, effective repairs and protect their property’s long-term value.

Step-by-Step Maintenance Checklist for Homeowners

Keeping concrete in good condition requires consistent care. Use this simple maintenance checklist to prevent small issues from becoming costly repairs:

• Inspect driveways & patios (Every 3 months): Walk around your home to check for new cracks or signs that existing ones are widening. Early detection helps prevent structural damage.
• Clean cracks & reseal (Annually): Use a pressure washer to remove dirt, debris, and mildew. Apply a high-quality concrete sealant to protect against moisture and weathering.
• Check for drainage issues (Bi-annually): After heavy rain, observe whether water pools near slabs or foundations. Redirect water flow with gutters, downspouts, or landscaping adjustments.
• Professional inspection (Every 2–3 years): Hire an expert to assess foundations, retaining walls, and larger cracks. Professional input ensures that underlying soil or structural concerns are addressed.

Following this checklist helps Australian homeowners extend the lifespan of their concrete surfaces while avoiding costly future repairs.

FAQs – Fixing Cracks in Concrete

How do I know if a concrete crack is serious?

If it’s wider than 5mm, growing over time, or in a load-bearing area, get it checked by a structural engineer.

Can I repair concrete cracks myself?

Yes, small cracks can be fixed with DIY fillers. Larger or structural cracks need professional repair.

How long will a repair last?

With proper materials, DIY repairs can last 3–10 years. Professional epoxy injection often lasts decades.

Is sealing concrete necessary after fixing cracks?

Yes, sealing prevents water infiltration, which is a major cause of recurring cracks.

Can termite or tree roots cause concrete cracks?

Yes, both can push against slabs, causing cracks that may reappear unless the source is addressed.

Conclusion

Concrete cracks are a common issue for Australian homeowners, but with the right approach, they don’t have to be costly or overwhelming. Minor cracks can often be managed with simple DIY kits, while larger or structural cracks should be addressed by professionals to ensure long-term stability.

By understanding the causes, choosing the right repair method, and taking preventive measures, you can keep your concrete driveways, patios, and floors looking great and functioning safely for years to come. For more guidance, check resources from Cement Concrete & Aggregates Australia (CCAA) and building advice from Your Home – Australian Government.

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