How to prevent concrete from cracking when it's drying

Concrete cracking is one of the biggest challenges on construction sites, and we’re sure you’ve seen it a few times in your career. Even well-executed pours can develop unwanted cracks during curing, leading to reduced durability, water ingress, and long-term maintenance problems. Understanding how to stop concrete cracking when drying is essential, not only to improve concrete performance but also to reduce costly work later down the line.

This guide explains the science behind drying shrinkage, the factors that accelerate cracking, and the strategies that significantly minimise risk. It also covers how to repair cracking concrete if cracks do form.

Why does concrete crack?

Concrete doesn’t simply “dry”, it goes through a process called hydration, where cement reacts with water to create a hardened mixture. As hydration progresses, moisture gradually leaves the concrete, causing it to shrink. This reduction in volume creates tensile stresses, especially where concrete is restrained by subgrade, reinforcement, or formwork. When those stresses exceed the concrete's tensile capacity, cracks begin to appear.

For large slabs, long pours, and structural elements, this restraint is unavoidable. The objective is to limit shrinkage and manage areas where cracks occur.

Drying shrinkage vs Plastic shrinkage

There are two main forms of shrinkage-driven cracking that affect new concrete. As concrete goes through its early setting and long-term drying stages, it can shrink in different ways, and each type of shrinkage creates its own pattern of cracks. These are:

• Plastic shrinkage cracking: Occurs within the first few hours. When surface evaporation exceeds the bleeding rate (the process where water rises to the surface of the poured concrete), the top layer shrinks and tears before the concrete has any tensile strength. These cracks are usually short, shallow, and random.
• Drying shrinkage cracking: Develops over months or years as moisture slowly evaporates from hardened concrete. This can cause wider cracks that interact with reinforcement or extend through the slab.

Environmental and material factors that increase concrete cracking

Environmental exposure and mix composition play a major role in early and long-term cracking. High temperatures, low humidity, wind, and poor moisture retention accelerate shrinkage, while unsuitable water–cement ratios or aggregate choices further increase stress within the concrete.

Evaporation, temperature, and wind

Harsh environmental conditions can increase cracking risk, which includes things like high temperatures, low humidity, direct sunlight, wind acceleration and surface moisture loss. Once evaporation rates go beyond 0.2 lb/ft²/hr, the chances of plastic shrinkage cracking increase. Warm temperatures above 28°C and wind speeds over 7 m/s can almost double evaporation rates, making early protection essential.

Water–cement ratio

Excess water is the leading cause of shrinkage-related cracking. High water–cement ratios make weaker, more permeable concrete with greater drying shrinkage. For structural concrete, a water-to-cement ratio of 0.35–0.45 is common. Higher ratios increase:

• Total shrinkage
• Carbonation (the reaction of carbon dioxide in the environment with calcium hydroxide in the cement) and long-term strength loss
• Susceptibility to early cracking

Cement content and aggregate selection

Because paste shrinks and aggregates don’t, mix designs with too much cement content or insufficient aggregate volume shrink more. 

Larger, well-graded aggregates, such as quartz, granite, and limestone, restrain shrinkage more effectively than softer stones, such as sandstone, which can absorb more water. This is because hard, dense aggregates provide a rigid internal structure that resists movement as the cement paste dries and contracts. Softer, more porous aggregates take in extra water, and when that water evaporates, it increases the total amount of shrinkage that the concrete experiences, making cracking more likely.

How to stop concrete cracking when drying

Preventing cracks during concrete curing requires an approach that combines multiple areas, like controlling moisture loss, optimising mix performance, and limiting internal stresses as the concrete hardens. By integrating the right admixtures, curing methods, reinforcement strategies, and joint planning, you can reduce plastic and drying shrinkage. 

This section outlines effective techniques used for stopping concrete from cracking while it dries.

Change the concrete mix design

There are a few ways you can change the mix design. One is by reducing the water content. Minimising the total water content is the most direct way to reduce shrinkage. It’s best to rely on superplasticisers for workability rather than adding water on site.

Another way is to lower cement content and use SCMs. With this, you increase the aggregate volume and incorporate SCMs such as fly ash, slag, or calcined clay to reduce paste content without losing performance. SCMs reduce the heat of hydration and long-term shrinkage.

It’s also important that you choose the right aggregates. Use well-graded, large aggregates to help meet drying shrinkage limits (≤0.075%).

Use Shrinkage-Reducing Admixtures (SRAs)

Shrinkage-reducing admixtures modify pore water surface tension, substantially lowering capillary stresses. At recommended dosages (around 1–2% by cement weight), SRAs can reduce drying shrinkage by up to 50%, helping you and your project!

SRAs are especially valuable for:

• Long-span slabs
• Exposed concrete floors
• High-performance mixes
• Structures in hot or windy climates

They integrate naturally into most mix designs and can complement other crack-control methods.

Effective curing

Proper curing ensures continuous hydration and limits cracking at the early stages. Concrete should be kept moist for 7–28 days, depending on environmental conditions.

Professional curing options include:

• Water-based or solvent-based curing compounds
• Wet burlap, mats, or continuous misting
• Temporary coverings such as polyethylene sheets

Wet curing is highly effective for slabs and exposed surfaces, while curing compounds are excellent for large areas or rapid application.

In hot or windy environments, it’s important to:

• Put up windbreaks
• Provide shade
• Schedule pours for early morning or late afternoon
• Cover the concrete immediately after finishing

These reduce evaporation and improve hydration by limiting airflow across the surface and lowering surface temperature through shade. Scheduling pours for cooler times of day means the concrete starts curing under gentler conditions, giving hydration a better chance to progress before heat and wind intensify. Covering the concrete immediately traps moisture at the surface, keeping it available for hydration and preventing the fast drying that can cause early shrinkage.

Apply evaporation retarders in critical conditions

Evaporation retarders are usually sprayed on fresh concrete to form a thin film that reduces moisture loss during the plastic stage. They sit on the surface of freshly placed concrete and slow the rate at which water escapes, giving the mix time to settle, bleed, and gain strength at this early stage. They are great when:

• Temperatures exceed 28°C
• Evaporation exceeds 0.2 lb/ft²/hr
• Wind speeds are high

These products help to stop early plastic shrinkage before finishing and curing are complete. 

Structural solutions that help stop concrete cracking

Beyond mix design and curing, structural measures also play a vital part in managing shrinkage. Reinforcement, fibres, and well-planned control joints distribute stresses throughout the slab and dictate where cracks can safely form.

Use reinforcement and fibres

Using steel reinforcements can be one way to help stop concrete cracking. Rebar and mesh distribute shrinkage stresses and reduce crack widths. However, proper placement is crucial, making sure that reinforcement near the top third of slabs controls crack distribution.

Steel and synthetic fibres provide microstructural restraint, helping to reduce plastic and drying shrinkage cracks. Typical dosage ranges are:

• steel fibres: 9–12 kg/m³
• synthetic macrofibres: 1.8–2.4 kg/m³

Install control joints correctly

It’s important to install control joints correctly because they force shrinkage cracks to form in predictable, controlled lines. Without joints, slabs will crack randomly. Here are some best practice tips for joint spacing:

• Joints should be spaced at 20–30 times the slab thickness.
• For 100 mm slabs, spacing should be 2–3 m.
• In warmer climates, reduce spacing to mitigate thermal movement.

Saw joints between 4–12 hours after placement. This means it’s late enough to avoid ravelling, but early enough to prevent uncontrolled cracking.

Subgrade and placement considerations

A stable, uniformly compacted subgrade and controlled placement conditions make sure that the concrete cures evenly and retains consistent support. Poor preparation or temperatures that are too extreme when you lay the concrete can cause tension, settlement, or rapid moisture loss, which can eventually lead to cracking.

Prepare a stable, well-compacted subgrade

Proper support is essential because settlement cracks usually originate from badly compacted or poorly drained subgrades. If the ground beneath a slab is uneven, loose, or retains too much water, the concrete can settle unevenly as it cures, creating tension that leads to cracks. To avoid this, make sure of the following:

• Removal of organic material: Roots, vegetation, or topsoil can decompose over time, leaving voids under the concrete. These voids create weak spots that can lead to uneven settlement and cracks. For example, pouring a slab over leftover tree roots may cause the slab to sink as the roots decay.
• Uniform compaction: Evenly compacted soil means that the slab is fully supported consistently. If some areas are loosely compacted, the concrete above them can settle more than the surrounding areas, resulting in cracking.
• Installation of a granular subbase (100 mm or more): A well-graded granular layer, such as crushed stone or gravel, improves load distribution and drainage. This reduces the risk of differential settlement and water-related damage.
• Adequate drainage provisions: If water accumulates under or around a slab, it can soften the subgrade and increase settlement, leading to cracks. Proper drainage channels or slopes help water move away from the concrete. For example, outdoor patios with poor drainage often develop cracking near downspouts or low spots where water collects.

Optimise placement and finishing conditions

For the best results, schedule pouring concrete when the weather will best aid your project. This includes laying in temperatures of 10°C–21°C, and avoiding pouring in extreme heat or cold weather to reduce the chance of thermal stresses and rapid evaporation. Once you’ve poured your concrete, begin the curing process as quickly as you can. Excessive finishing can delay curing and increase plastic shrinkage risk.

How to repair cracking concrete

Even when every precaution is taken, minor cracking can still develop, unfortunately. This is because concrete naturally shrinks and responds to environmental stresses, and even the best mix design and curing methods can’t completely eliminate all cracking. The good news is that most minor cracks are manageable, and there are effective ways you can treat them. Here are a few ways to do so:

• Epoxy injection for structural cracks: Low-viscosity epoxy injection can help restore the structure and prevent water from entering. This is suitable for cracks that run through the depth of the concrete or compromise load-bearing performance.
• Polymer-modified and epoxy repair mortars: For wider surface cracks or spalls, use trowel-grade polymer or epoxy mortars to rebuild the concrete section and restore durability.
• Joint sealants for non-structural cracks: Elastomeric sealants prevent moisture ingress in hairline or non-structural cracks

Monitoring cracks for movement, widening, or moisture penetration helps determine whether repairs are necessary.

Get the right support for crack-free concrete today

Achieving durable, high-performance concrete starts with using the right techniques and materials. Whether you're pouring new slabs, managing complex site conditions, or repairing defects, having access to trusted professional-grade products makes all the difference.

For specialist solutions, explore our full range of concrete repair products designed for remediation tasks. If you need tailored guidance for your project, our team is here to help. Contact us today, and we’ll support you with expert advice.