ASTM C946-23

Standard Practice for Construction of Dry-Stacked, Surface-Bonded Walls

ABSTRACT
This practice covers material, workmanship, and construction procedures for applying surface bonded mortar to both sides of dry stacked concrete masonry units. Mortar shall be mixed and shall be selected in accordance with the proportion specification prescribed. Shims shall be corrosion-resistant metal or plastic with a required minimum compressive strength. Courses of concrete masonry units between the leveling courses shall be placed without mortar on the bed or head joints. Place units in running bond. Remove burrs and butt blocks tightly. Use shims, mortar, or surface bonding mortar to plum and level individual units when necessary. Use clean mixing equipment and water free of deleterious amounts of acid, alkali, and organic materials. Mix only full bag multiples of material to overcome any segregation of ingredients. Mixing time shall be kept to a minimum, as over mixing may cause damage to the fibers. Before applying surface bonding mortar, wet the wall uniformly with water to prevent excessive suction of water from the surface bonding mortar. Trowel- or spray-apply surface bonding mortar to both sides of dry-stacked concrete masonry units. When a second coat of surface bonding mortar is to be applied, the first coat shall have taken its initial set. Dampen the wall with a water mist after a specified time, but within a day of application of surface bonding mortar. The top of the walls shall be covered with a nonstaining, waterproof covering to prevent moisture from entering the wall until the top is permanently protected.
SCOPE
1.1 This practice covers material, workmanship, and construction procedures for applying surface bonded mortar to both sides of dry stacked concrete masonry units. It does not include grout, reinforcing, anchorage, or control joints since their use is essentially the same as conventional concrete masonry construction, unless specifically mentioned in this practice.  
Note 1: Design and construction procedures for conventional concrete masonry construction are found in Building Code Requirements for Masonry Structures (TMS 402-16) and Specification for Masonry Structures (TMS 602-16).  
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2023
• ICS: 91.060.10 - Walls. Partitions. Facades
• Technical Committee: C12 - Mortars and Grouts for Unit Masonry
• Drafting Committee: C12.06 - Surface Bonding

Relations

• Refers: ASTM C90-23 - Standard Specification for Loadbearing Concrete Masonry Units
• Effective Date: 01-Dec-2023
• Refers: ASTM C129-23 - Standard Specification for Nonloadbearing Concrete Masonry Units
• Effective Date: 01-Dec-2023
• Refers: ASTM C55-23 - Standard Specification for Concrete Building Brick
• Effective Date: 01-Dec-2023
• Refers: ASTM C887-19a - Standard Specification for Packaged, Dry, Combined Materials for Surface Bonding Mortar
• Effective Date: 01-Dec-2019
• Refers: ASTM C887-19 - Standard Specification for Packaged, Dry, Combined Materials for Surface Bonding Mortar
• Effective Date: 01-Jun-2019
• Refers: ASTM C270-19ae1 - Standard Specification for Mortar for Unit Masonry
• Effective Date: 01-May-2019
• Refers: ASTM C270-19a - Standard Specification for Mortar for Unit Masonry
• Effective Date: 01-May-2019
• Refers: ASTM C270-19 - Standard Specification for Mortar for Unit Masonry
• Effective Date: 01-Feb-2019
• Refers: ASTM C1714/C1714M-19 - Standard Specification for Preblended Dry Mortar Mix for Unit Masonry
• Effective Date: 15-Jan-2019
• Refers: ASTM C1714/C1714M-16 - Standard Specification for Preblended Dry Mortar Mix for Unit Masonry
• Effective Date: 15-Dec-2016
• Refers: ASTM C55-16 - Standard Specification for Concrete Building Brick
• Effective Date: 01-Dec-2016
• Refers: ASTM C90-16 - Standard Specification for Loadbearing Concrete Masonry Units
• Effective Date: 15-Jul-2016
• Refers: ASTM C90-15 - Standard Specification for Loadbearing Concrete Masonry Units
• Effective Date: 15-Dec-2015
• Refers: ASTM C270-14a - Standard Specification for Mortar for Unit Masonry
• Effective Date: 15-Dec-2014
• Refers: ASTM C129-14a - Standard Specification for Nonloadbearing Concrete Masonry Units
• Effective Date: 01-Dec-2014

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.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C946 − 23
Standard Practice for
Construction of Dry-Stacked, Surface-Bonded Walls
This standard is issued under the fixed designation C946; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope C270 Specification for Mortar for Unit Masonry
C887 Specification for Packaged, Dry, Combined Materials
1.1 This practice covers material, workmanship, and con-
for Surface Bonding Mortar
struction procedures for applying surface bonded mortar to
C1714/C1714M Specification for Preblended Dry Mortar
both sides of dry stacked concrete masonry units. It does not
Mix for Unit Masonry
include grout, reinforcing, anchorage, or control joints since
2.2 Other Documents:
their use is essentially the same as conventional concrete
TMS 402-16 The Masonry Society, Building Code Require-
masonry construction, unless specifically mentioned in this
ments for Masonry Structures
practice.
TMS 602-16 The Masonry Society, Specification for Ma-
NOTE 1—Design and construction procedures for conventional concrete
sonry Structures
masonry construction are found in Building Code Requirements for
TEK 10-2C National Concrete Masonry Association, Con-
Masonry Structures (TMS 402-16) and Specification for Masonry Struc-
trol Joints for Concrete Masonry Walls—Empirical
tures (TMS 602-16).
Method
1.2 The values stated in inch-pound units are to be regarded
Standard Practice for Bracing Masonry Walls Under Con-
as standard. The values given in parentheses are mathematical
struction, Masonry Contractors Association of America,
conversions to SI units that are provided for information only
and are not considered standard.
1.3 This standard does not purport to address all of the
3. Storage
safety concerns, if any, associated with its use. It is the
3.1 Deliver and store surface bonding mortar in original
responsibility of the user of this standard to establish appro-
containers off the ground to prevent contact with water. Protect
priate safety, health, and environmental practices and deter-
from rain with suitable covering.
mine the applicability of regulatory limitations prior to use.
3.2 Store concrete masonry units off the ground to prevent
1.4 This international standard was developed in accor-
contamination by mud, dust, and materials likely to cause
dance with internationally recognized principles on standard-
staining or other defects, and protect from rain.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
4. Materials and Manufacture
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 4.1 Concrete masonry units shall be clean and shall meet the
requirements of either Specifications C55, C90, or C129. The
2. Referenced Documents
surface to receive surface bonding mortar shall be free of paint,
oil, efflorescence, or foreign materials that interfere with
2.1 ASTM Standards:
bonding.
C55 Specification for Concrete Building Brick
C90 Specification for Loadbearing Concrete Masonry Units
4.2 Surface bonding mortar shall meet the requirements of
C129 Specification for Nonloadbearing Concrete Masonry
Specification C887. If the dry mix contains hard lumps, it shall
Units
not be used.
4.3 Leveling course shall be bedded with a mortar meeting
This practice is under the jurisdiction of ASTM Committee C12 on Mortars and
Specification C270, Specification C887, or Specification
Grouts for Unit Masonry and is the direct responsibility of Subcommittee C12.06 on
C1714/C1714M.
Surface Bonding.
Current edition approved June 1, 2023. Published June 2023. Originally
approved in 1981. Last previous edition approved in 2018 as C946 – 18. DOI:
10.1520/C0946-23. Available from The Masonry Society, www.masonrysociety.org
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from the National Concrete Masonry Assn. (NCMA), 13750 Sunrise
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Valley Drive, Herndon, VA 20171, http://www.ncma.org.
Standards volume information, refer to the standard’s Document Summary page on Available from Masonry Contractors Association of America (MCAA), 1481
the ASTM website. Merchant Drive, Algonquin, IL 60102, http://www.masoncontractors.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C946 − 23
4.4 Shims shall be corrosion-resistant metal or plastic with 7. Mixing Surface Bonding Mortar
a minimum compressive strength of 2000 psi (13.8 MPa), or
7.1 Use clean mixing equipment and water free of deleteri-
steel protected from corrosion by a coating of zinc at least 0.8
ous amounts of acid, alkali, and organic materials.
2 2
oz/ft (2.4 gm/mm ), or by a coating of cadmium or zinc of
7.2 Surface bonding mortar shall be mixed according to the
equivalent corrosion resistance.
manufacturer’s instructions and used within the time recom-
mended by the manufacturer.
5. Leveling Courses
7.3 Mix only full bag multiples of material to overcome any
5.1 Leveling courses, when needed, are to provide a smooth
1 segregation of ingredients while in the package.
surface level within ⁄4 in. (6.35 mm) in 20 ft (6.1 m), for dry
stacking concrete masonry units. Leveling courses shall be
7.4 Mixing time shall be kept to a minimum, as over-mixing
located whenever a vertical difference greater than ⁄2 in. (12.7
may cause damage to fibers in Specification C887 mortar.
mm) in 10 ft (3.0 m) occurs within one course. Leveling
7.5 Hand Mixing:
courses are usually located on the first course above the
7.5.1 Place water in the mixing container.
foundation, because footings are not normally placed in a level
7.5.2 Slowly add the dry surface bonding material.
condition, and at each floor level.
7.5.3 Mix thoroughly.
5.2 When Specification C270 mortar or surface bonding
7.6 Machine Mixing:
mortar is used a leveling course, concrete masonry units shall
7.6.1 Place water in mixer.
be set in a full bed of mortar, laid to a line with the top surface
7.6.2 Add the surface bonding material to the operating
level, as defined in 5.1, and butted together with no mortar in
mixer.
the hea
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C946 − 18 C946 − 23
Standard Practice for
Construction of Dry-Stacked, Surface-Bonded Walls
This standard is issued under the fixed designation C946; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers material, workmanship, and construction procedures for applying surface bonded mortar to both sides of
dry stacked concrete masonry units. It does not include grout, reinforcing, anchorage, or control joints since their use is essentially
the same as conventional concrete masonry construction, unless specifically mentioned in this practice.
NOTE 1—Design and construction procedures for conventional concrete masonry construction are found in Building Code Requirements for Masonry
Structures (TMS 402-16) and Specification for Masonry Structures (TMS 602-16).
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C55 Specification for Concrete Building Brick
C90 Specification for Loadbearing Concrete Masonry Units
C129 Specification for Nonloadbearing Concrete Masonry Units
C270 Specification for Mortar for Unit Masonry
C887 Specification for Packaged, Dry, Combined Materials for Surface Bonding Mortar
C1714/C1714M Specification for Preblended Dry Mortar Mix for Unit Masonry
2.2 Other Documents:
TMS 402-16 The Masonry Society, Building Code Requirements for Masonry Structures
TMS 602-16 The Masonry Society, Specification for Masonry Structures
TEK 10-2C National Concrete Masonry Association, Control Joints for Concrete Masonry Walls—Empirical Method
This practice is under the jurisdiction of ASTM Committee C12 on Mortars and Grouts for Unit Masonry and is the direct responsibility of Subcommittee C12.06 on
Surface Bonding.
Current edition approved June 1, 2018June 1, 2023. Published July 2018June 2023. Originally approved in 1981. Last previous edition approved in 20102018 as
C946 – 10.C946 – 18. DOI: 10.1520/C0946-18. 10.1520/C0946-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from The Masonry Society, www.masonrysociety.org
Available from the National Concrete Masonry Assn. (NCMA), 13750 Sunrise Valley Drive, Herndon, VA 20171, http://www.ncma.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C946 − 23
Standard Practice for Bracing Masonry Walls Under Construction, Masonry Contractors Association of America, 2012
3. Storage
3.1 Deliver and store surface bonding mortar in original containers off the ground to prevent contact with water. Protect from rain
with suitable covering.
3.2 Store concrete masonry units off the ground to prevent contamination by mud, dust, and materials likely to cause staining or
other defects, and protect from rain.
4. Materials and Manufacture
4.1 Concrete masonry units shall be clean and shall meet the requirements of either Specifications C55, C90, or C129. The surface
to receive surface bonding mortar shall be free of paint, oil, efflorescence, or foreign materials that interfere with bonding.
4.2 Surface bonding mortar shall meet the requirements of Specification C887. If the dry mix contains hard lumps, it shall not be
used.
4.3 Leveling course shall be bedded with a mortar meeting either Specification C270 or , Specification C887, or Specification
C1714/C1714M.
4.4 Shims shall be corrosion-resistant metal or plastic with a minimum compressive strength of 2000 psi (13.8 MPa), or steel
2 2
protected from corrosion by a coating of zinc at least 0.8 oz/ft (2.4 gm/mm ), or by a coating of cadmium or zinc of equivalent
corrosion resistance.
5. Leveling Courses
5.1 Leveling courses, when needed, are to provide a smooth surface level within ⁄4 in. (6.35 mm) in 20 ft (6.1 m), for dry stacking
concrete masonry units. Leveling courses shall be located whenever a vertical difference greater than ⁄2 in. (12.7 mm) in 10 ft (3.0
m) occurs within one course. Leveling courses are usually located on the first course above the foundation, because footings are
not normally placed in a level condition, and at each floor level.
5.2 When Specification C270 mortar or surface bonding mortar is used a leveling course, concrete masonry units shall be set in
a full bed of mortar, laid to a line with the top surface level, as defined in 5.1, and butted together with no mortar in the head joints.
Bed joints shall be struck flush. If the cores are to be grouted, no mortar shall be placed in the space to receive grout.
5.3 Allow the levelling mortar to set sufficiently so no movement breaks the bond while dry stacking units in subsequent courses.
6. Dry-Stacking Concrete Masonry Units
6.1 Courses of concrete masonry units between the leveling courses shall be placed without mortar on the bed or head joints. Place
units in running bond. Remove burrs and butt blocks tightly.
6.2 Use shims, mortar, or surface bonding mortar to plumb and level individual units when necessary.
6.3 Check the wall every fourth course to be certain it is plumb and level. If any course is out of level by more than ⁄2 in. (12.7
mm) in 10 ft (3.0 m), another leveling course shall be built.
6.4 Cut masonry units to fit openings. Minimum length of cut piece used in the wall sha
...