31st Jan 2024 -

With any material exposed to the elements, concrete is susceptible to damage over time. Cracks, crumbling and erosion can occur because of factors like weather, ground movement and improper installation. Performing timely repairs is essential for maintaining structural integrity and preventing further deterioration.  

This article provides practical guidance on repairing common defects using mortar and cement products. Proper repair techniques, materials selection, surface prep and application are covered in detail. With the right methods and products, wall foundations, concrete paving slabs and other elements can be restored to an attractive, long-lasting state.

What is the issue with repairing concrete?

Repairing cracked, crumbling or deteriorating concrete often presents some common challenges. Being aware of these potential issues and the remedies can help ensure successful repairs. 

1. Bonding problems

New patching mortar mix not adhering properly to the old concrete is a frequent challenge. If you do not clean the surface thoroughly, the patch cannot bond properly. Solutions include thoroughly cleaning the concrete with a wire brush and chiselling out the interface. Use a grinder or acid etch to roughen the surface below for new mortar. Also, use concrete bonding agents before patching to tackle the issue. 

2. Cracks reappearing

Cracks that return after repairs indicate issues like ongoing ground movement, improper surface prep or an unstable substrate. To solve the problem, start by identifying the main cause. After that, enlarge the crack and shape the edges. This will create a stronger area for the repair. Plus, you can use flexible patching compounds like epoxy injections for subgrade reinforcement. Install expansion or control joints nearby to isolate forces and add steel reinforcements in certain patches.

3. Patching spalling

Concrete spalling is when the surface pops off in flakes or chunks, often from water damage. Spalling repairs require meticulously chiselling or chipping away all loose material until only solid remains. In addition, applying a bonding agent to integrate with the substrate. Also, patching with a polymer-modified cementitious compound that withstands weathering.

4. Matching appearance

Differences in texture, colour, and overall appearance between patchwork and original concrete are common eyesores. Resolutions include using colouring additives and mortar tinting pigments to closely match existing shades. Also, other solutions include imprinting or texturing the patches to simulate the surrounding surface. Plus, you can conceal repairs with cladding, stucco, stone or overlay tiles.

5. Curing problems

The cement-based mortar needs proper moisture and time to cure and gain full strength. Prevent drying too quickly by misting repaired areas, tenting or plastic-wrapping repairs. This contains moisture and allows adequate cure time before traffic or water exposure. 

Which is the best concrete for repair work?

Using the right type is important for achieving the strongest, longest-lasting repairs. Here are some guidelines for selecting the optimal concrete mix. 

Ready mix concrete 

  • The easiest repair option, requiring only water addition on-site.
  • Contains polymers and aggregates engineered for bonding with old concrete.
  • Shrinkage-compensated to minimise cracking.
  • Best for surface-level repairs up to 40mm deep.

Fibre concrete

  • Contains synthetic fibres (polypropylene or glass) that increase flexural strength and impact resistance.
  • Allows it to flex slightly without cracking. This makes it ideal for repairing slabs and structures that experience movement or vibration.
  • Used for structural repairs where steel rebar has corroded.

High-strength concrete

  • Formulated with low water-cement ratio for extremely high compressive strength. Typically, it is 4000 pounds per square inch (psi).
  • Ideal for rebuilding damaged supports, columns, beams and foundational elements that require enhanced load capacity.

Latex-modified concrete

  • Contains latex polymer emulsion for incredible bond strength and flexibility.
  • Excellent adhesion properties make it the go-to choice for applying concrete overlays to an existing slab.
  • Increased resilience allows application as thin as 6mm overlays.

Flowable micro-concrete

  • Flowable, grout-like consistency injects easily into damaged areas and cracks.
  • High-strength, ultra-fine components fill voids for structural strengthening.
  • Used to gravity-feed cracks and damaged spots before applying surface-level patches.

How to repair concrete: Step-by-step guide

The arm of a construction worker wearing a bright orange glove holding a cement float for a concrete repair wall job.

Here is a step-by-step guide on repair work, including tools to use and how to mix concrete. 

Step 1 - Gather tools and materials

Safety gogglesCement
Wire brushDust mask
Margin trowelStiff-bristle brush
BucketChisel and hammer

Step 2 - Assess the damage

Look at the whole area to understand the type of damage. This could be cracks, chips, holes, spalling or crumbling. Decide if small, surface-level patching is enough or if deeper repair is necessary. Sound out hollow or damaged areas. Consider whether cavity repair requires additional reinforcing.

Step 3 - Mark out repair area

Use a chalk line or straight board to mark cut lines around the entire damaged area. Extend the outline 50-75mm to encapsulate weak edges prone to further cracking. Lines should form a rectangular shape. Be sure to avoid thin and irregular shapes.

Step 4 - Cut out repair area

Make repeated passes with the masonry chisel and hammer or power chisel along cut lines. You should aim for a depth of 13mm or the depth of damage. Use a chisel with a wide blade to undercut cavity edges by 13mm to prevent future cracking. Be sure to clean away all chipped concrete until only solid, stable material remains.

Step 5 - Clean the cavity

Use a hand wire brush or powered wire wheel to scrub the repair area. Remove all loose crumbs and chunks, exposing bare, rough concrete for maximum bonding. Clear away dust, oils, curing compounds or coatings from the original pour. Make sure to clean the rebar thoroughly if exposed. 

Step 6 - Apply bonding agent

Apply bonding agent evenly to all repair surfaces using a brush or roller, following product instructions.  Work compound fully into roughened concrete. Extend the bonding agent 50mm beyond the repair edges. Allow the area to cure fully before placement of fresh mixture.

Step 7 - Mix repair compound

With a cement mixer or hand mixing, mix the amount of concrete with lime mortar and cement mixture. Add water gradually until you achieve a workable consistency. However, it is important to not overwater. Only blend an amount that you can place within 15-20 minutes before the mix begins to set.

Step 8 - Moisten concrete substrate

Use a pump sprayer to lightly dampen the cavity before filling. Do not saturate the area, just mist the fresh patch because it should not dry too prematurely.

Step 9 - Fill the cavity

Fill the repair area about 13mm deep with concrete, tamping with a trowel float to compress. Build up thin layers when repair is over 50mm deep. You need to fully compact each layer. Next, fill the cavity fully to the surface, overfilling slightly to allow for consolidation. Mound mix above the surface to promote downward packing and blending.

Step 10 - Shape and blend edges

Use a trowel angled about 30 degrees from the surface to smooth the patch and integrate it with the surrounding concrete. Blend and feather edges into old concrete to prevent cold joints. Texture and finish surface to match existing concrete.

Step 11 - Allow proper cure time

Mist the surface lightly with small amounts of water for 3-7 days to slow moisture loss as concrete cures. Avoid heavy loads or vibration near repair for the recommended time per specifications. Protect fresh concrete from freezing, rain and water while gaining strength.

How long does concrete last?

With proper installation, correct mix and diligent maintenance, concrete should last 50 years or more. Several factors impact its durability.

Concrete quality

  • Higher-strength concrete made with a low water-cement ratio will be denser and last longer. Be sure to aim for at least 4000 psi.
  • Using higher-quality ingredients like ordinary Portland cement, clean aggregates and minimal mixing water increases durability.

Environmental exposure

  • Concrete is more durable in hot, dry climates than in colder climates with freezing and thawing cycles that harm it.
  • In northern areas, salt used for deicing can corrode rebar and erode concrete from the inside. Therefore, more deterioration can occur.

Loading conditions

  • A residential path or driveway made with strong concrete will last longer than an industrial floor. The industrial floor has lots of traffic and heavy equipment.

Maintenance frequency

  • Performing routine maintenance like sealing, cleaning and making minor repairs as soon as issues appear extends service life significantly. 

6 concrete maintenance tips

  • Cure new concrete thoroughly for at least 7 days. Use wet burlap or plastic sheets to prevent premature moisture evaporation. 
  • Reseal exterior concrete every 2-3 years with a suitable silane or silicone-based sealer. This will protect against moisture and chloride intrusion, which corrodes concrete from the inside over time.
  • Perform crack repairs promptly using epoxy injection or suitable cementitious fillers. They prevent further damage from freeze-thaw cycles penetrating cracks.
  • As soon as possible, remove oil, grease, or chemical stains to prevent the concrete pores from absorbing them. Use cleaning agents made specifically for concrete.
  • Address all spall, pit and damaged areas early before additional erosion occurs. Make repairs to restore the integrity and appearance.
  • Maintain proper drainage and slope around foundations and slabs. Water should drain fully away and not penetrate the concrete to prevent settlement cracks.

Order concrete and mortar repair materials today

We offer various mortar mixes, ready-to-use cement, and concrete repair materials at Building Materials Nationwide. Our extensive selection encompasses top-notch products that excel in durability and performance, ensuring effective solutions for various repair construction projects.

To find a trustworthy supplier, explore the advantages of opening a trade account with us. You gain access to trade account management service, fast UK delivery options and competitive trade pricing. We provide ready mix mortar, cement and reinforced concrete materials for your projects to help you succeed. Sign up for instant access or contact us to ask any questions.

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