How to Avoid Scaling, Spalling, and Surface Problems in Concrete

Concrete is a reliable building material, but like anything exposed to the elements, it can suffer from wear and tear. Scaling and spalling are common surface issues that concrete contractors face, especially when moisture, freezing conditions, or improper mixing and curing are involved. While they often start out as cosmetic problems, if left untreated, they can lead to deeper structural issues that compromise the structural integrity of the concrete.

The good news is that these issues are entirely preventable with the right techniques, tools, and know-how. By ensuring consistent mixing, proper curing, and using the right practices, you can avoid the costly repairs associated with scaling and spalling problems.

What Are Scaling and Spalling?

What Scaling Looks Like

Concrete scaling occurs when the top layer of the concrete surface flakes off due to stress from the freeze-thaw cycle or improper curing. This is often a cosmetic problem, meaning it doesn’t always impact the structural integrity of the concrete. But if moisture keeps entering the slab, the problem can worsen.

Scaling can manifest as small, shallow patches where the surface layer begins to peel off. If untreated, this problem can expand as moisture seeps in, which may lead to deeper surface damage.

What Spalling Looks Like

Unlike scaling, concrete spalling is a more serious issue. The spalling process happens when chunks of concrete break off, often exposing the steel reinforcement bars (rebar) underneath. Spalling concrete is usually the result of rebar corrosion, internal pressure, and moisture intrusion. Over time, spalling can compromise the concrete structure, causing ongoing deterioration and potential structural failure.

The severity of concrete spalling depends on its depth. If it reaches the steel reinforcement, it can compromise the compressive strength of the concrete and affect the overall stability of the concrete foundation.

What’s the Difference?

Why Concrete Scales and Spalls (Root Causes)

Improper Water Ratios and Poor Mixing Practices

The most common cause of scaling and spalling is improper mixing. If the water-to-cement ratio is off, the concrete will either be too watery or too dry, both of which lead to weak surfaces.

• Too much water: Excess water dilutes the mix, reducing the compressive strength of the concrete and creating a porous surface. This makes it easier for moisture to infiltrate, which can lead to spalling.

• Too little water: When there’s not enough water in the mix, the concrete becomes too dry, and the paste doesn’t bond properly with the aggregates. This weakens the overall structure and can cause surface cracking or scaling.

A consistent mix is key to a strong and durable concrete slab.

Poor Finishing Practices

Finishing concrete before the bleed water has evaporated can trap excess moisture in the surface layer, weakening the concrete. When this moisture evaporates, it leaves behind small voids or gaps, making the surface more prone to scaling.

Waiting until the bleed water has evaporated and the surface has started to set properly before finishing will ensure a stronger and more durable top layer.

Improper Curing

Concrete needs to be properly cured to retain moisture and allow the material to form a strong bond. If curing is done improperly, the concrete can dry out too quickly, causing shrinkage cracks that allow water to enter, leading to spalling concrete.

Proper curing requires that the surface be kept moist during the first few days. This helps prevent dryness and reduces the risk of water penetration, which can weaken the concrete.

Environmental Factors + Deicing Salts

Environmental conditions such as freeze-thaw cycles can also contribute to the breakdown of concrete. When moisture inside the concrete freezes, it expands, causing internal pressure that forces the concrete to crack and scale. This can cause significant damage over time.

The use of deicing salts accelerates this process by chemically reacting with the concrete, breaking down the surface and making it more prone to scaling and spalling. For the first season, avoid using deicing salts on fresh concrete to prevent these environmental factors from damaging your slab.

Why Batch Variation Leads to Weak Surfaces

With traditional drum mixers, batch variation can be a significant issue. As you pour multiple batches of concrete, the water content can vary, leading to inconsistent mix ratios. This inconsistency creates weak surface layers, especially when later batches become wetter, resulting in weak concrete that is more susceptible to surface issues.

By ensuring a consistent water-to-mix ratio, you can eliminate these weak spots, resulting in a stronger, more uniform slab. This is where the MudMixer stands out.

How to Prevent Scaling and Spalling

Get the Water-to-Mix Ratio Right

A consistent water-to-mix ratio is key to preventing weak surfaces. Traditional mixers can create batch-to-batch variation, leading to inconsistent mix ratios and, ultimately, weakened concrete. The MudMixer Evolution solves this problem with its adjustable water dial, allowing you to set and maintain the water level throughout the mixing process. This ensures that your concrete has the correct consistency every time.

Strengthen Curing Practices

Proper curing is key to long-lasting concrete.

• Keep the surface moist: During the early curing phase, ensure that the surface remains moist to prevent shrinkage cracks and water infiltration.

• Use curing blankets: In high-temperature environments, use curing blankets or membranes to maintain moisture levels in the concrete during the curing process.

Pro Tips: Explore Best Practices for Concrete Curing 

Protect New Concrete Early

• Avoid de-icing salts: For the first season, avoid using de-icing salts on freshly poured concrete to prevent moisture intrusion and freeze-thaw damage.

• Apply topical sealers: Once the curing is complete, use a topical sealer to provide an extra layer of protection against moisture and deicing chemicals.

Repair Options If You Already Have Spalling

Assess the Depth of Damage (Cosmetic vs Structural)

If spalling has already occurred on the concrete slab, assess the depth of the damage to determine the best course of action for concrete repair.

• Light Surface Scaling: Shallow, cosmetic damage can often be repaired without needing structural intervention.

• Deep Spalling with Rebar Exposure: If the damage exposes the steel rebar or the spalling is deep, this indicates possible significant damage that may require structural repair.

Signs of Spalled Concrete and What to Do

Light to Moderate Surface Repair Methods

#1 Repair mortar and patching compounds: For light surface scaling, these methods are effective at restoring the surface.

#2 Concrete overlays: Used for more extensive surface damage, overlays provide an additional layer of protection and durability.

Severe Damage or Active Corrosion

If the concrete shows signs of deep spalling and exposed rebar, or if active rebar corrosion is present, concrete replacement may be required. This is the most expensive option, but necessary for structural integrity.

Cost Considerations

How MudMixer Supports Stronger, Longer-Lasting Concrete Surfaces

The MudMixer offers several advantages that help contractors avoid surface problems like scaling and spalling:

• Consistent water ratio: The adjustable water dial provides precise control over your concrete mix, preventing weak surface layers.

• Continuous-feed design: Unlike traditional drum mixers, the MudMixer provides consistent mixing without batch-to-batch variation.

• Faster mixing: The MudMixer’s continuous-feed system speeds up the mixing process, allowing for quicker finishing and curing.

• Better control: Fewer callbacks and reduced repair risk thanks to its precise mix control.