ASTM C933-23

Standard Specification for Welded Wire Lath

ABSTRACT
This specification covers welded wire lath, flat or self-furring, with or without backing, designed for use as a base to receive Portland cement-based interior plaster and exterior stucco. Welded wire lath shall be fabricated from cold-drawn, galvanized steel wire, conforming to the referenced specification. The wire shall be zinc-coated and the backling shall be attached to the lath to prevent accidental removal during shipping, handling, or installation. The thickness of the embedment of the lath and plaster shall be measured from the back plane of the back wire, exclusive for furring, to the backing or surface of the substrate.
SCOPE
1.1 This specification covers welded wire lath, flat or self-furring, with or without backing, designed for use as a base to receive portland cement-based interior plaster and exterior stucco.  
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 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: 30-Sep-2023
• ICS: 77.140.65 - Steel wire, wire ropes and link chains
• Technical Committee: C11 - Gypsum and Related Building Materials and Systems
• Drafting Committee: C11.02 - Specifications and Test Methods for Accessories and Related Products

Relations

• Replaces: ASTM C933-18 - Standard Specification for Welded Wire Lath
• Effective Date: 01-Oct-2023
• Referred By: ASTM C1063-23 - Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster
• Effective Date: 01-Oct-2023
• Referred By: ASTM C841-23 - Standard Specification for Installation of Interior Lathing and Furring
• Effective Date: 01-Oct-2023
• Referred By: ASTM C1780-23a - Standard Practice for Installation Methods for Cement-based Adhered Masonry Veneer
• Effective Date: 01-Oct-2023

Overview

ASTM C933-23: Standard Specification for Welded Wire Lath is an internationally recognized standard developed by ASTM International. This specification covers the requirements for welded wire lath, both flat and self-furring varieties, used as a supportive base for Portland cement-based interior plaster and exterior stucco applications. The standard outlines the composition, dimensions, physical properties, packaging, marking, and quality assurance characteristics necessary to ensure the structural performance and reliability of welded wire lath in both residential and commercial construction projects.

Welded wire lath, according to ASTM C933-23, is fabricated from cold-drawn, galvanized steel wire. It can be supplied with or without factory-attached backing materials such as water-resistive barriers. These barriers, when present, enhance the performance of the lath in demanding stucco and plaster installations.

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Key Topics

• Material Requirements:
  Welded wire lath must be manufactured from cold-drawn, zinc-coated (galvanized) steel wire that complies with specific ASTM and federal standards for thickness, coating, and durability.

• Construction & Dimensions:

  • Openings within the lath are restricted to a maximum of 2 x 2 inches (51 mm x 51 mm).
  • Reinforcement may be added parallel to the lath’s long dimension, improving strength and durability.
  • The lath may include self-furring crimps that project from the back, providing space for plaster embedment.
  • Standard dimensions are strictly defined to ensure compatibility with various wall assemblies.

• Water-Resistive Barrier Backing:
  When provided, the factory-attached backing must adhere securely to the lath and meet specified requirements for water resistance and bursting strength. This backing is critical in exterior stucco systems to manage moisture and prevent detachment during shipping or installation.

• Packaging & Marking:
  Bundles or rolls of welded wire lath are to be visibly and permanently marked with details such as manufacturer, country of origin, product description, mesh size, and wire thickness, ensuring traceability and compliance verification.

• Inspection, Sampling, and Rejection:
  The standard includes guidelines for sampling and inspecting products, as well as procedures for identifying and reporting nonconforming materials.

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Applications

Welded wire lath specified by ASTM C933-23 plays a vital role in modern construction by providing a stable base for Portland cement-based plasters and stucco. Key applications include:

• Exterior Stucco Systems:
  Providing necessary reinforcement and anchorage for cement-based stucco on building exteriors, enhancing durability and resistance to cracking.

• Interior Plaster Walls and Ceilings:
  Serving as a supportive grid that helps plaster or render bond securely to substrates in both residential and commercial interiors.

• Masonry Veneer Base:
  Used as an intermediate layer to support thin masonry or stone veneer installations over wood or steel framing.

This standard ensures that welded wire lath components perform reliably, readily integrating with industry best practices for moisture management and structural stability.

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Related Standards

• ASTM A641/A641M: Standard Specification for Zinc-Coated (Galvanized) Carbon Steel Wire, referenced for material quality and galvanization requirements.
• ASTM C11: Terminology Relating to Gypsum and Related Building Materials and Systems, used for consistent language and definitions.
• ASTM E2556/E2556M: Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers, applicable to optional factory-attached backings.
• Federal Specification UU-B-790: Building Paper for water-resistant backing material.

For additional details, consult the latest version of ASTM C933-23 and the above referenced standards to ensure compliance, safety, and performance in all applications involving welded wire lath systems.

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: C933 − 23
Standard Specification for
Welded Wire Lath
This standard is issued under the fixed designation C933; 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 4. Materials and Manufacture
4.1 Welded wire lath shall be fabricated from not less than
1.1 This specification covers welded wire lath, flat or
0.0625 in. (1.588 mm), cold-drawn, galvanized steel wire,
self-furring, with or without backing, designed for use as a base
to receive portland cement-based interior plaster and exterior conforming to Specification A641/A641M.
4.1.1 Diameter tolerance for galvanized wire shall be in
stucco.
accordance with Specification A641/A641M.
1.2 The values stated in inch-pound units are to be regarded
4.1.2 The wire shall be zinc-coated (galvanized) in accor-
as standard. The values given in parentheses are mathematical
dance with Specification A641/A641M.
conversions to SI units that are provided for information only
4.1.3 If provided, the factory-attached water-resistive bar-
and are not considered standard.
rier shall conform to Federal Specification UU-B-790 or
1.3 This international standard was developed in accor-
ASTM Specification E2556/E2556M. The water-resistive bar-
dance with internationally recognized principles on standard-
rier shall be either absorptive or water resistant. The water-
ization established in the Decision on Principles for the
resistive barrier shall have a bursting strength of not less than
Development of International Standards, Guides and Recom-
that required to maintain integrity under normal hand- or
mendations issued by the World Trade Organization Technical
machine-application pressures.
Barriers to Trade (TBT) Committee.
4.1.4 If provided, the factory-attached water-resistive bar-
rier shall be attached to the lath to prevent accidental removal
2. Referenced Documents
during shipping, handling or installation. Attachment of the
2.1 ASTM Standards:
water-resistive barrier shall allow lapping of wire-to-wire and
A641/A641M Specification for Zinc–Coated (Galvanized)
water-resistive barrier to water-resistive barrier of not less than
Carbon Steel Wire
one mesh at ends and edges and shall permit full embedment,
C11 Terminology Relating to Gypsum and Related Building
in not less than ⁄4 in. (6 mm) of plaster, of not less than
Materials and Systems
one-half of the total length and width of the wire.
E2556/E2556M Specification for Vapor Permeable Flexible
4.1.5 The thickness of the embedment of the lath and plaster
Sheet Water-Resistive Barriers Intended for Mechanical
shall be measured from the back plane of the back wire,
Attachment
exclusive of furring, to the water-resistive barrier or surface of
2.2 Federal Specifications:
the substrate.
UU-B-790 Building Paper, Vegetable Fiber: (Kraft,
5. Dimensions and Permissible Variations
Waterproofed, Water Repellent and Fire Resistant)
5.1 Openings and Stiffening:
3. Terminology
5.1.1 Lath shall be welded at all intersections of wire to
3.1 Definitions of terms used in this standard shall be in
form openings not more than 2 in. by 2 in. (51 mm by 51 mm).
accordance with Terminology C11.
5.1.2 Reinforced lath shall be permitted to be reinforced
continuously and parallel to the long dimension of the lath at
This specification is under the jurisdiction of ASTM Committee C11 on
intervals of not more than 6 in. (150 mm). Wires used for this
Gypsum and Related Building Materials and Systems and is the direct responsibility
purpose shall range from 0.072 in. to 0.1205 in. (1.9 mm to
of Subcommittee C11.02 on Specifications and Test Methods for Accessories and
3.1 mm). Reduction of the size of the openings to less than
Related Products.
Current edition approved Oct. 1, 2023. Published November 2023. Originally 2 in. by 2 in. (51 mm by 51 mm) shall also be permitted.
approved in 1980. Last previous edition approved in 2018 as C933 – 18. DOI:
5.1.3 Self-furring crimps on self-furring lath shall project
10.1520/C0933-23.
not less than ⁄4 in. (6 mm) from the plane of the back of the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
lath.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
5.2 Thickness—The nominal thickness shall be ⁄8 i
...

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: C933 − 18 C933 − 23
Standard Specification for
Welded Wire Lath
This standard is issued under the fixed designation C933; 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*Scope
1.1 This specification covers welded wire lath, flat or self-furring, with or without backing, designed for use as a base to receive
portland cement-based interior plaster and exterior stucco.
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 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:
A641/A641M Specification for Zinc–Coated (Galvanized) Carbon Steel Wire
C11 Terminology Relating to Gypsum and Related Building Materials and Systems
E2556/E2556M Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers Intended for Mechanical Attachment
2.2 Federal Specifications:
UU-B-790 Building Paper, Vegetable Fiber: (Kraft, Waterproofed, Water Repellent and Fire Resistant)
3. Terminology
3.1 Definitions of terms used in this standard shall be in accordance with Terminology C11.
4. Materials and Manufacture
4.1 Welded wire lath shall be fabricated from not less than 0.0625 in. (1.588 mm), cold-drawn, galvanized steel wire, conforming
to Specification A641/A641M.
4.1.1 Diameter tolerance for galvanized wire shall be in accordance with Specification A641/A641M.
4.1.2 The wire shall be zinc-coated (galvanized) in accordance with Specification A641/A641M.
This specification is under the jurisdiction of ASTM Committee C11 on Gypsum and Related Building Materials and Systems and is the direct responsibility of
Subcommittee C11.02 on Specifications and Test Methods for Accessories and Related Products.
Current edition approved Oct. 1, 2018Oct. 1, 2023. Published October 2018November 2023. Originally approved in 1980. Last previous edition approved in 20142018
as C933 – 14.C933 – 18. DOI: 10.1520/C0933-18.10.1520/C0933-23.
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 Standardization Documents Order Desk, Bldg. 4 Section D, 700 Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C933 − 23
4.1.3 The If provided, the factory-attached water-resistive barrier shall conform to Federal Specification UU-B-790 or ASTM
Specification E2556/E2556M. The water-resistive barrier shall be either absorptive or water resistant. The water-resistive barrier
shall have a bursting strength of not less than that required to maintain integrity under normal hand- or machine-application
pressures.
4.1.4 The If provided, the factory-attached water-resistive barrier shall be attached to the lath to prevent accidental removal during
shipping, handling or installation. Attachment of the water-resistive barrier shall allow lapping of wire-to-wire and water-resistive
barrier to water-resistive barrier of not less than one mesh at ends and edges and shall permit full embedment, in not less than ⁄4
in. (6 mm) of plaster, of not less than one-half of the total length and width of the wire.
4.1.5 The thickness of the embedment of the lath and plaster shall be measured from the back plane of the back wire, exclusive
of furring, to the water-resistive barrier or surface of the substrate.
5. Dimensions and Permissible Variations
5.1 Openings and Stiffening:
5.1.1 Lath shall be welded at all intersections of wire to form openings not more than 2 by 2 in. (512 in. by 2 in. (51 mm by
51 mm).
5.1.2 Reinforced lath shall be permitted to be reinforced continuously and parallel to the long dimension of the lath at intervals
of not more than 6 in. (150 mm). Wires used for this purpose shall range from 0.0720.072 in. to 0.1205 in. (1.9(1.9 mm to 3.1 mm).
Reduction of the size of the openings to less than 2 by 2
...