Brick Classification, Properties, and Selection

Why Brick Classification Matters

Choosing the wrong brick for a job is not just a quality issue — it is a structural and safety issue. A brick that cannot handle freeze-thaw cycling will spall, weaken the wall, and create falling hazards. Understanding how bricks are classified under ASTM standards, and how to read those classifications against a project specification, is a core competency for every mason.

ASTM Standards That Govern Brick

Two ASTM standards cover most of the brick you will work with on residential and commercial projects.

ASTM C62 — Building Brick applies to solid masonry units used where appearance is not the primary concern: backup wythe, structural cores, retaining walls, and similar applications. C62 establishes three grades based on resistance to weathering:

• SW (Severe Weathering): Highest durability. Use where brick will be exposed to freezing temperatures while wet — below grade, at grade, or in regions with frequent freeze-thaw cycles.
• MW (Moderate Weathering): Intermediate durability. Suitable for above-grade exterior use in climates where freezing is infrequent or the brick is unlikely to be saturated.
• NW (Negligible Weathering): Lowest durability. Intended for interior use only, where the brick will not be exposed to weather.

ASTM C216 — Facing Brick covers brick selected primarily for its appearance in exposed wall surfaces. C216 shares the SW/MW weathering grades but adds a dimension tolerance classification:

• FBS (Face Brick Standard): The most common facing brick. Moderate variation in size and surface texture is acceptable.
• FBX (Face Brick Extra): Tighter dimensional tolerances and smoother appearance. Specified when close-tolerance coursing or a refined look is required.
• FBA (Face Brick Architectural): Intentional non-uniformity in size, texture, and color for a rustic or artistic effect. Specifications call for samples to be approved before delivery.

ASTM C902 — Pedestrian and Light Traffic Paving Brick covers brick intended for flatwork such as walkways, patios, and courtyards. Grades are designated by application (e.g., Class SX for severe exposure, Class MX for moderate exposure) rather than the SW/MW/NW system. Always check the current ASTM standard for the specific grade designations when specifying paving brick.

Physical Properties That Drive Selection

Beyond grade, several physical properties influence brick selection:

• Compressive Strength: Measured in psi, it tells you how much load the unit can carry. SW-grade building brick must meet the minimum compressive strength set out in ASTM C62.
• Water Absorption: Expressed as a percentage of dry weight. Lower absorption generally means higher durability in freeze-thaw conditions. ASTM C62 and C216 set maximum absorption limits by grade.
• Saturation Coefficient (C/B ratio): The ratio of 24-hour cold-water absorption to 5-hour boiling absorption. A lower ratio indicates the unit has more unfilled pore space to accommodate ice expansion, making it more freeze-thaw resistant. SW brick has a lower allowable saturation coefficient than MW brick.
• Dimensions: Standard modular brick is nominally 4 × 2-2/3 × 8 inches, with actual dimensions of 3-5/8 × 2-1/4 × 7-5/8 inches. The difference between nominal and actual accounts for the mortar joint.

Standard Mortar Joint and the 3/8-Inch Rule

The standard mortar joint in brick masonry is 3/8 inch. This joint thickness is built into the modular dimension system: one course of standard modular brick plus one 3/8-inch mortar joint equals 2-2/3 inches in height. When you calculate brick quantities, you always work with the nominal dimensions (which include the joint), not the actual brick face dimensions alone.

Selecting Brick for Common Applications

Always match the ASTM grade to the exposure condition:

| Application | Recommended Grade |

|---|---|

| Exterior veneer, freeze-thaw climate | SW (C216) |

| Exterior veneer, mild climate | MW or SW (C216) |

| Interior partition, no weather exposure | NW (C62) or FBS/MW (C216) |

| Paved courtyard, exterior | Class SX or MX (C902) |

| Architectural accent wall, varied texture | FBA (C216) |

When a project specification references an ASTM standard and grade, use it exactly — substituting a lower grade to save money is a code violation and a safety risk.

Safety Points

Personal Protective Equipment (PPE): Always wear safety glasses or goggles when handling brick samples, cutting brick, or working near masonry operations. Brick dust and silica particles are hazards — in dusty environments wear an N95 or higher respirator rated for silica dust. Wear work gloves to protect against abrasion and cuts from sharp edges.

Housekeeping: Broken or spalled bricks create trip and cut hazards. Keep the work area clear. Stack samples on a stable, flat surface so they cannot tip or fall.

Lifting: Standard bricks weigh 4–5 pounds each. Use proper lift mechanics — straight back, lift with the legs — when moving sample sets or full cubes of brick.