Spalling Concrete and How to Fix It

Spalling or spalled concrete is frequently encountered when coating or lining a concrete substrate.

High Performance Coatings

Concrete Spalling: Understanding, Preparing, and Repairing with Modern Solutions

Concrete spalling is a common challenge that contractors and facility managers face when maintaining or renovating concrete structures. Understanding how to properly identify, prepare, and repair spalled concrete is crucial for ensuring long-lasting results and successful coating applications.

What is Concrete Spalling?

A spall within a concrete surface is technically defined as "a fragment, usually in the shape of a flake, detached from a larger mass by a blow, by the action of weather, by pressure, or by expansion within the larger mass." These defects are categorized by size:

Small spalls: Roughly circular depressions not greater than 20 mm in depth and 150 mm in any dimension
Large spalls: May be circular, oval, or elongated, measuring more than 20 mm in depth and 150 mm in greatest dimension

When spalling occurs, it's essential to address it properly before applying any coating or lining to ensure optimal adhesion and performance.

Pre-Repair Assessment: The Foundation of Success

Before jumping into repairs, a thorough evaluation of the concrete substrate is crucial. This assessment should include:

Visual Inspection

Detailed examination of the cleaned concrete surface
Documentation of spall locations and sizes
Identification of patterns that might indicate underlying issues

Damage Assessment

Physical damage evaluation
Chemical damage or attack identification
Contamination detection
Concrete defects and curing issues
Moisture concerns
Structural integrity evaluation
Reinforcing steel condition assessment

Surface Preparation: Following Industry Standards

Proper surface preparation is the key to successful concrete repair and coating applications. Two critical industry standards guide this process:

SSPC-SP13/NACE 6 Surface Preparation of Concrete

This standard outlines the required degree of cleanliness for concrete surfaces prior to coating or repair application.

ICRI 310.2R Selecting and Specifying Concrete Surface Preparation

This document governs the level of profile required and provides acceptable means and methods to achieve various surface conditions. The ICRI CSP (Concrete Surface Profile) coupons offer visual representations of required surface profiles, complementing the technical specifications.

Choosing the Right Repair Material

Product selection is critical to repair success. Consider these factors when selecting repair materials:

Project-specific service conditions and exposures
Required application thicknesses
Curing schedules and timeline constraints
Compatibility with subsequent coating or lining materials
Environmental conditions during and after application

The CSA Cement Advantage: A Modern Solution

Calcium sulfoaluminate (CSA) cements represent a significant advancement in concrete repair technology. These materials, such as Tnemec's Series 217 MortarCrete, offer several key advantages:

Rapid Strength Development

CSA cements typically achieve near-target 28-day strength in as little as 24 hours, making them ideal for projects requiring quick return to service.

Low Shrinkage Properties

The unique chemistry of CSA cements results in minimal shrinkage during curing. While requiring a higher water-to-cement ratio than Portland cement, CSA cements consume most of this water during hydration, significantly reducing bleed water and associated shrinkage issues.

Environmental Benefits

CSA cements are more environmentally friendly than traditional Portland cements:

Clinker is softer, requiring less energy for grinding
Lower kiln temperatures needed: 1250°C (2250°F) versus 1500°C (2700°F) for Portland cement
Reduced carbon footprint in manufacturing

Application Versatility

Products like Series 217 MortarCrete offer:

Application thickness range from 1/4 inch to 4 inches in a single lift
High chemical resistance compared to other cementitious repair mortars
Ability to accept coatings and linings after just 12 hours at 75°F
Excellent performance in various exposure conditions

Concrete Repair and Resurfacing Blog

Best Practices for Concrete Repair Success

Always start with proper assessment - Understanding the extent and cause of damage is crucial
Follow surface preparation standards - Use SSPC/NACE and ICRI guidelines as your roadmap
Select materials based on project requirements - Consider all factors including timeline, exposure, and subsequent coatings
Consider CSA cements for time-sensitive projects - Their rapid cure and high early strength can significantly reduce downtime
Document your work - Keep records of materials used, application conditions, and any challenges encountered

Conclusion

Successful concrete spall repair requires a systematic approach combining proper assessment, surface preparation, and material selection. Modern CSA cement-based products offer significant advantages for many applications, particularly where rapid return to service is critical. By following industry standards and selecting appropriate materials, contractors can ensure durable, long-lasting repairs that provide an excellent substrate for protective coatings and linings.

References

AMPP (2021) SSPC-SP13/NACE 6 Surface Preparation of Concrete
ICRI (2021) 310.2R-2013 Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays and Concrete Repair
Tnemec (2004) StrataShield Installation & Application Guide Resinous Flooring
Tnemec (2021) Tnemec Series 217 MortarCrete Product Data Sheet

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