A brick wall is only as strong as the weakest brick in it. Yet on most Bangladeshi construction sites, bricks are accepted or rejected on nothing more than a glance and a knock — a habit that has quietly caused cracked plaster, damp walls, and premature masonry failure in buildings that otherwise met every structural drawing to the letter.
Brick quality control is not a formality; it is a field discipline, and it takes about fifteen minutes per truckload to get right.This guide walks through exactly how a site engineer verifies brick quality before allowing a single unit into the wall, referencing the classification and test requirements used in Bangladeshi practice under BNBC 2020 and BDS 208:2009 (Specification for Common Building Clay Bricks), alongside the visual and physical checks every mason and engineer should know by heart.
Why Brick Quality Control Matters More Than It Gets Credit For
Bricks carry compressive load, resist moisture penetration, and hold plaster and render without cracking — three jobs that a poorly burnt or under-fired brick simply cannot do. A batch of under-strength or high-absorption bricks will not fail the day the wall goes up; it fails two monsoons later, as efflorescence stains the plaster, mortar joints erode, and hairline cracks start telegraphing through the finish coat. By then, the remedy is demolition and rebuilding, not a warranty claim against the brick supplier. Catching the problem at the truck, before the bricks are laid, is the only point in the process where rejection actually costs less than acceptance.
Classification of Bricks Used in Bangladeshi Construction
Before checking quality, an engineer needs to know which class of brick the specification actually calls for, since acceptance criteria change with class. Bangladeshi practice — closely aligned with BDS 208:2009 and the technical specifications referenced under BNBC — recognizes four broad grades:
| Brick Class | Avg. Compressive Strength | Water Absorption (24 hr) | Typical Use |
|---|---|---|---|
| First Class | 105–140 kg/cm² (≈10–14 N/mm²) minimum | Not more than 15–20% by dry weight | Load-bearing walls, exposed brickwork, and RCC infill panels |
| Second Class | 70–100 kg/cm² (≈7 N/mm²) minimum | Not more than 22% | Plastered walls, internal partitions, non-critical work |
| Third Class | 35–70 kg/cm² | 20–25%, high efflorescence risk | Temporary structures, low-rainfall areas only — avoid in RCC frame infill |
| Picked Jhama (over-burnt, vitrified) | 170–210 kg/cm² average | Not more than 15% | Foundation soling, road sub-base, coarse aggregate in lean concrete |
For any structural or load-bearing masonry — including the infill panels between RCC columns that dominate mid-rise construction in Dhaka — first-class brick is the only grade an engineer should be approving without a formal waiver on record.
Step-by-Step Field Procedure for the Site Engineer
Every incoming truckload should go through this sequence before it is unloaded into the storage stack. None of these checks needs a laboratory; all but one can be done on-site in under twenty minutes with a bucket of water, a weighing scale, and two bricks.
Step 1 — Visual and Dimensional Inspection
Pull ten random bricks from different points in the load, not just the top layer. Check for:
- Uniform, deep red or copper colour with no black or grey under-burnt patches
- Sharp, true rectangular edges — no rounded corners or warping
- No visible cracks, chips, embedded pebbles, or lime nodules
- Consistent size within tolerance of the standard modular dimension used by the supplier (typically 240 × 115 × 70 mm or the local kiln's stated size)
Step 2 — The Ringing Sound Test
Strike two bricks together edge-to-edge. A well-burnt brick produces a clear, sharp metallic ring. A dull, thudding sound signals an under-burnt or cracked brick that will underperform in compressive strength regardless of what the lab report says.
Step 3 — The Scratch (Hardness) Test
Drag a fingernail firmly across the brick face. A properly fired brick will show no visible scratch mark. If the nail leaves a groove, the brick is under-burnt and will not meet the minimum compressive strength.
Step 4 — The Drop Test
Lift a brick to about one metre and let it fall onto hard ground. A good brick should not break into fragments; at most, it should split cleanly into two pieces. Bricks that shatter fail this test outright.
Step 5 — Water Absorption Test
This is the single most predictive field test available without a lab, and it should be run on every new supplier or every major delivery, not just once per project.
- Weigh a dry brick sample and record the mass (W1).
- Fully submerge it in clean water for 24 hours.
- Remove, wipe off surface water with a damp cloth, and weigh again within three minutes (W2).
- Calculate absorption: [(W2 − W1) / W1] × 100
First-class bricks intended for structural or exposed work should not exceed roughly 15–20% absorption by dry weight. Bricks absorbing much less than about 10% can also be a problem — they may not bond properly with mortar — so absorption is checked for a reasonable range, not just a ceiling.
Step 6 — Efflorescence Test
Stand a brick on end in a dish with about 25 mm of water and let it stand in a warm, ventilated space until the water is fully absorbed or evaporated. Refill and repeat once. Inspect the exposed surface:
- Nil — no visible deposit — acceptable
- Slight — deposit covers under 10% of the surface — acceptable for most work
- Moderate — 10–50% coverage — acceptable only for non-critical, plastered work
- Heavy or Serious — over 50% coverage, with surface powdering — reject the batch
Efflorescence is a direct warning sign of soluble salt content in the clay, and it is the single biggest cause of stained, deteriorating exterior plaster in coastal and low-lying areas of Bangladesh.
Step 7 — Compressive Strength (Lab Verification)
Field tests screen out obviously bad batches, but structural acceptance still needs a formal crushing test. Send a representative sample (typically 5–8 bricks per lot) to an accredited lab, following procedures aligned with ASTM C67 or the equivalent BDS method. Record both the average strength and the lowest individual result — a single weak brick in the sample often points to inconsistent kiln temperature across the batch, which means the whole lot deserves closer scrutiny, not just the tested pieces.
Step 8 — Soundness Check on Fracture
Break one brick from the sample and examine the broken face. It should show a homogeneous, compact texture with no visible air holes, lime lumps, or layering. A fractured surface with grit, voids, or laminations indicates poor clay preparation and predicts poor long-term durability even if the crushing test passes.
Common Site Mistakes That Let Bad Bricks Through
- Sampling only the top of the stack — suppliers sometimes load better bricks on top; always pull samples from the middle and bottom of the truck.
- Skipping the water absorption test on repeat suppliers — kiln quality varies batch to batch, even from the same source.
- Accepting third-class brick for RCC frame infill to save cost, without a documented design waiver from the structural engineer.
- Ignoring efflorescence in the dry season — the salts are still present in the clay; they simply have not yet been triggered by moisture.
- Relying only on a lab report from the supplier without independent site verification, especially the ringing and scratch tests, which take seconds and catch batch-to-batch inconsistency, a monthly lab certificate will miss.
Quick Reference: Acceptance Criteria Summary
| Test | Tool Needed | Pass Criteria (First Class) |
|---|---|---|
| Ringing sound | None | Clear metallic ring |
| Scratch/hardness | Fingernail | No visible mark |
| Drop test | None (1 m height) | No shattering; clean split at most |
| Water absorption | Weighing scale, water tank | ≤15–20% by dry weight |
| Efflorescence | Dish, water | Nil to slight |
| Compressive strength (lab) | Compression testing machine | ≥105 kg/cm² average |
Frequently Asked Questions
What is the minimum compressive strength of first-class brick under Bangladeshi practice?
First-class brick is generally expected to achieve an average compressive strength of at least 105 kg/cm² (roughly 10–10.5 N/mm²), with no individual test result falling significantly below that average.
How long should a water absorption test run?
The standard immersion period is 24 hours in clean water at room temperature, with the sample weighed immediately before submersion and again within a few minutes of removal and surface drying.
Can bricks with moderate efflorescence still be used?
Moderate efflorescence is generally tolerated only in non-critical, fully plastered internal work. For exposed brickwork, exterior walls, or any structural application, nil-to-slight efflorescence should be the acceptance threshold.
Is a supplier's lab certificate enough to accept a delivery?
A certificate confirms one sample from one point in time. Site-level checks — ringing sound, scratch test, and a spot water absorption test — should still be run on every major delivery, since kiln output quality can vary considerably batch to batch.
Why do low water absorption bricks also raise concern?
Bricks with unusually low absorption (well under 10%) may bond poorly with mortar, since the brick needs to draw some moisture from the mortar to achieve a proper mechanical key. Extremely dense, low-absorption units sometimes need pre-wetting before laying.
This article is part of an ongoing series on construction quality control referenced to BNBC 2020 by the engineering team at BNF Engineers Ltd. For related reading, see our articles on precast versus cast-in-situ pile foundations under BNBC 2020, and use our rebar weight calculator for reinforcement takeoffs.
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