Why Brick Strength Matters More Than Price

Executive summary

Brick and block pricing is easy to compare. Structural performance is not—and that’s where costly failures happen. Brick compressive strength (measured in MPa) is one of the simplest, most important indicators of whether a masonry unit is fit for its intended use. In South Africa, deemed-to-satisfy wall construction under the National Building Regulations is tied to minimum average compressive strengths for masonry units (with different thresholds for single-storey, double-storey lower storey, and free-standing walls).

Paying less per brick can look like savings—until weak units lead to cracking, water penetration, rework, delays, rejected inspections, or disputes over “defects” that are actually material selection or workmanship issues. The regulations are explicit that walls must be designed/constructed to safely sustain actions and resist water penetration where it would affect durability or health, and deemed-to-satisfy compliance is achieved by meeting SANS 10400-K’s requirements.

This article explains what MPa means, how strength is tested and certified, how to select an appropriate strength class for common applications (including walling and paving), and why higher-quality units usually reduce total lifecycle cost and risk.

What MPa means and how brick strength is tested

Compressive strength describes how much compressive stress a unit can resist before failure. Higher compressive strength generally increases the strength and stiffness of the masonry assemblage (wall system), though overall wall performance also depends on mortar, workmanship, design detailing, and support conditions.

How testing works in practice

• For clay brick (workmanship principles that still matter): Technical guidance notes that compressive strength is determined using standardized test methods (e.g., ASTM C67/C67M), with the brick oriented horizontally as it sits on the bed joint during construction.

• For concrete bricks and blocks in South Africa: AfriSam’s technical note states that the governing standard for concrete masonry units is SANS 1215, covering physical requirements and sampling for testing, and that assurance of compliance is obtained through the SABS Certification Mark showing units are produced under controlled conditions and verified through accredited testing.

• For concrete paving blocks: The Concrete Society of South Africa summarizes that SANS 1058:2012 is the current specification for concrete paving blocks and requires compliance with dimensional tolerances, abrasion resistance, absorption criteria, and performance classes (commonly expressed as 30/2.0 and 40/2.6 based on tensile splitting strength).

  
  

Why strength matters more than price

1. Structural safety and code compliance

South Africa’s wall regulations emphasize structural strength and stability: walls must be designed and constructed to safely sustain actions and limit damage (including cracking) so doors/windows still function and weather tightness is not compromised.

SANS 10400-K provides deemed-to-satisfy “packages” where minimum unit strengths are part of compliance. Examples include:

• Certain building wall scenarios: ≥3.0 MPa (hollow) and ≥4.0 MPa (solid) average compressive strength.

• Lower storey of certain double-storey scenarios: ≥7.0 MPa (hollow) and ≥10 MPa (solid) average compressive strength.

• Free-standing/retaining/parapet/balustrade walls: ≥3.0 MPa (hollow) and ≥5.0 MPa (solid) average compressive strength.

  
  

These values cannot be used in isolation: the standard ties them to other conditions (wall thickness, roof loads, storey heights, detailing, and more).

2. Durability, water resistance, and maintenance

Higher strength often correlates with improved durability because material standards set minimum strengths partly to ensure durable performance (and many units exceed minimum requirements).

Durability isn’t only about “not collapsing.” It’s about minimizing:

• Repeated repair of cracks and loose joints

• Moisture ingress and damp-related finishes damage

• Chipping/breakage during handling and installation

  
  

For paving blocks specifically, the Concrete Society of South Africa notes that while compressive strength (e.g., “25 MPa blocks”) may be structurally adequate in many cases, the tensile splitting test can better indicate performance—and strength should be increased in certain environments to improve durability.

3. Resale value and perception of quality

Buildings with visible structural cracking, damp staining, and recurring repairs tend to face buyer skepticism and valuation pushback. While resale value is influenced by many factors, better-performing masonry reduces the likelihood of defects that erode buyer confidence, especially where regulations explicitly target cracking and weather tightness as performance outcomes.

4. Legal and contract risk

The “cheap brick” problem often becomes a dispute problem:

• If unit strength or certification cannot be demonstrated, buyers may face rejections under contract specs or difficulty proving compliance.

• SANS 10400-K is explicitly positioned as the deemed-to-satisfy route for Part K compliance of the National Building Regulations.

• Choosing products that can show SANS compliance and certification reduces ambiguity during inspections and handover.

Common misconceptions about price vs performance

Misconception: “A brick is a brick—if it looks okay, it’s fine.”

Appearance does not confirm compressive strength, controlled manufacturing, or compliance testing. AfriSam notes that assurance of compliance with SANS 1215 is achieved by obtaining the SABS Certification Mark and associated testing under controlled conditions.

Misconception: “Higher MPa is always better.”

Higher MPa is often beneficial, but “best” depends on application, wall type, and design constraints. SANS 10400-K uses different minimum strengths for different wall scenarios, proving that selection is context-based—not one-size-fits-all.

Misconception: “Low-strength units only cause problems in extreme loads.”

Low-strength masonry can create practical failures long before a structural “collapse,” such as breakage during handling, crushing at concentrated bearing points, unacceptable cracking, and persistent water penetration risk. The Concrete Society of South Africa specifically highlights early handling breakage as a reason for strength development requirements in paving manufacture and selection.

Selecting the right strength for common applications

1. Practical selection table

Application (typical)	What to specify	Baseline reference
Single-storey / certain dwelling wall scenarios (deemed-to-satisfy conditions apply)	Average compressive strength ≥3.0 MPa (hollow) and ≥4.0 MPa (solid) where SANS 10400-K conditions are met	SANS 10400-K deemed-to-satisfy requirements 1
Double-storey lower storey (deemed-to-satisfy conditions apply)	Average compressive strength ≥7.0 MPa (hollow) and ≥10 MPa (solid) where SANS 10400-K conditions are met	SANS 10400-K 1
Boundary / garden / certain retaining walls (and parapets/balustrades)	Average compressive strength ≥3.0 MPa (hollow) and ≥5.0 MPa (solid), plus geometric limits and detailing requirements	SANS 10400-K (also contains specific retaining/boundary wall design limits) 1
Concrete bricks/blocks procurement baseline	Confirm SANS 1215 compliance; note minimum strength guidance (blocks ≥3.5 MPa; bricks ≥7 MPa) and seek SABS certification	AfriSam technical note on bricks/blocks 3
Interlocking paving for driveways vs industrial yards	Specify SANS 1058 compliance and the correct class (commonly 30/2.0 or 40/2.6 based on tensile splitting strength); match thickness to traffic (often 60 mm pedestrian/light use, 80 mm vehicular)	Concrete Society of South Africa summary of SANS 1058 classes + ICPI thickness guidance 5

2. Real-world product signaling: what reputable listings show

A practical indicator of “strength transparency” is whether suppliers declare strength classes and standards:

• Corobrik lists concrete bricks/blocks as SABS Certified and aligned to SANS 1215:2008, with declared strengths such as 7 or 14 MPa for cement maxi bricks and 3.5 or 7 MPa for certain concrete blocks.

• For paving, Corobrik lists an 80 mm interlocking paver to SANS 1058 with performance options like 40/2.6 and 30/2.0 (crushing/tensile MPa), aligned to heavy-duty applications.

These aren’t just “marketing specs”—they are procurement information that reduces ambiguity between design intent, site reality, and inspection.

Cost-benefit: the lifecycle view that contractors win with

“Cheaper per unit” can become more expensive when you count:

• Higher breakage (handling, stacking, loading)

• Slower productivity (sorting rejects, rework)

• Remedial works (crack repairs, damp rectification, rebuild sections)

• Inspection delays and contract deductions

  
  

When performance issues arise, it’s often hard to claim a manufacturing defect if the wrong product was selected for the application or if compliance evidence is missing. SANS 10400-K explicitly links compliance to meeting its deemed-to-satisfy requirements.

For paving manufacture and performance, the Concrete Society of South Africa notes that cheaper materials (including waste materials) may come at the expense of quality or increase costs by requiring higher cement contents to maintain performance.

Recommended specifications and what to request from a supplier

Keep these specs short and verifiable:

• Walling units: Specify the needed average compressive strength using SANS 10400-K for the wall type/storey, and require confirmation of compliance.

• Concrete bricks/blocks: Confirm SANS 1215 compliance and ask for evidence of controlled production (e.g., SABS Certification Mark / relevant documentation).

• Paving blocks: Specify SANS 1058 compliance and the correct class for the application environment (30/2.0 vs 40/2.6), plus appropriate thickness for traffic.

• Storage and handling: Store materials off the ground and cover with tarps/water-resistant protection to reduce contamination and moisture-driven defects.

Buyer checklist

Use this six-point checklist before placing an order:

1. Confirm wall type and storey (single-storey vs double-storey lower storey) and match unit strengths to SANS 10400-K deemed-to-satisfy requirements where applicable.

2. Ask for proof of compliance: concrete units to SANS 1215, and whether production is under certified/controlled conditions (SABS Certification Mark where applicable).

3. Verify the supplier declares unit strength (MPa) clearly on quotes/invoices/spec sheets (avoid “unknown strength” materials).

4. For paving, specify SANS 1058 class (30/2.0 or 40/2.6) and appropriate thickness for traffic category.

5. Plan storage: keep packs off the ground and covered to prevent contamination, saturation, and staining risk.

6. Document delivery condition and store correctly—many disputes are prevented by photos, signed delivery notes, and immediate reporting of transport damage.