ASTM C946-23 PDF

Overview

ASTM C946-23 is the standard practice developed by ASTM International for the construction of dry-stacked, surface-bonded walls using concrete masonry units (CMUs). This standard details the material requirements, workmanship expectations, and construction procedures for applying surface-bonded mortar to both sides of dry-stacked CMUs. The standard does not cover aspects such as grout, reinforcing, or control joints unless specifically mentioned. ASTM C946-23 facilitates more efficient masonry wall systems by eliminating conventional mortar joints, relying instead on fiber-reinforced surface bonding mortars for structural stability, weather resistance, and finished appearance.

Key Topics

• Material Specifications:

  • Concrete masonry units must be clean and meet ASTM standards such as C55, C90, or C129.
  • Surface bonding mortar must comply with ASTM C887 or equivalent specifications.
  • Leveling course mortar should meet ASTM C270, C887, or C1714/C1714M standards.
  • Shims used should be corrosion-resistant and must have a minimum compressive strength as specified.

• Workmanship and Construction Procedures:

  • Units between leveling courses are to be dry-stacked without traditional mortar on bed or head joints, set in running bond.
  • Leveling and plumbing of units is achieved with shims, mortar, or surface bonding mortar as necessary.
  • Before applying surface bonded mortar, uniformly dampen the wall to prevent excessive suction.
  • Surface bonding mortar shall be applied (trowel or spray) to a minimum specified thickness on both wall surfaces.
  • If two coats are needed, the first must reach an initial set before application of the second.

• Mixing and Application:

  • Use only clean mixing equipment and water free from harmful materials.
  • Mix the mortar according to manufacturer’s instructions, using full bag multiples to ensure homogeneity.
  • Over-mixing should be avoided to protect reinforcing fibers within the mortar.

• Curing and Protection:

  • Walls should be protected from extreme temperatures and covered from weather exposure during and after construction.
  • Fog misting within the first 24 hours is necessary to ensure proper curing.
  • Ensure tops of walls are covered with nonstaining, waterproof covers until permanent protection is in place.

Applications

The ASTM C946-23 standard provides a reliable method for constructing dry-stacked masonry walls with surface-bonded mortar, offering significant practical benefits:

• Speed of Construction: With no bed or head joints, walls can be stacked quickly and efficiently.
• Cost Efficiency: Reduces labor and material costs by eliminating traditional mortar joints and simplifying processes.
• Improved Structural Performance: The use of fiber-reinforced surface bonding mortars enhances wall integrity, crack resistance, and weather protection.
• Versatility: Suitable for use in loadbearing and nonloadbearing wall systems in residential, commercial, and institutional projects.
• Aesthetics and Durability: Surface bonding mortar provides a smooth, uniform finish and increases the wall’s durability and resistance to weather penetration.

Related Standards

For professionals and organizations implementing or referencing ASTM C946-23, several related standards and documents provide complementary technical guidance:

• ASTM C55 - Specification for Concrete Building Brick
• ASTM C90 - Specification for Loadbearing Concrete Masonry Units
• ASTM C129 - Specification for Nonloadbearing Concrete Masonry Units
• ASTM C270 - Specification for Mortar for Unit Masonry
• ASTM C887 - Specification for Surface Bonding Mortar
• ASTM C1714/C1714M - Specification for Preblended Dry Mortar Mix for Unit Masonry
• TMS 402-16 - Building Code Requirements for Masonry Structures
• TMS 602-16 - Specification for Masonry Structures
• NCMA TEK 10-2C - Control Joints for Concrete Masonry Walls

By following ASTM C946-23, construction teams can achieve efficient, high-performance dry-stacked masonry wall systems with enhanced durability and consistent quality.