ASTM C1063: Installation of Lathing and Furring Standard
ASTM C1063 is the primary American standard governing the installation of lathing and furring used as a base for portland cement plaster (stucco) systems. Published by ASTM International, the standard establishes dimensional tolerances, fastener schedules, substrate preparation requirements, and inspection criteria that apply across residential and commercial stucco applications in the United States. Compliance with C1063 is referenced directly in the International Building Code and is enforced through local permitting and inspection processes in jurisdictions nationwide.
Definition and scope
ASTM C1063, titled Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster, defines the minimum performance requirements for the lathing substrate layer that supports all subsequent coats in a portland cement plaster assembly. The standard is published and maintained by ASTM International and undergoes periodic revision; the most recent edition in wide circulation is the C1063-21 revision.
The scope of C1063 covers:
- Vertical and soffit surfaces on both interior and exterior assemblies
- Metal lath types, including expanded metal lath, sheet lath, and rib lath
- Wire fabric lath, including welded wire and woven wire configurations
- Gypsum board lath used as a plaster base in interior applications
- Furring channels and systems that create a planar substrate over irregular structural surfaces
The standard does not govern the composition or application of the plaster coats themselves — those are addressed by companion documents including ASTM C926 (Application of Portland Cement-Based Plaster) and ASTM C897 (Aggregate for Job-Mixed Portland Cement-Based Plasters).
Within the stucco repair and installation service landscape, C1063 functions as the foundational installation reference. Work that deviates from C1063 requirements at the lathing stage is a primary source of system failures including delamination, cracking, and moisture infiltration.
How it works
C1063 structures installation requirements through a sequential set of specifications tied to substrate type, lath category, and structural framing geometry.
1. Substrate assessment and preparation
Before lath installation begins, framing members must meet maximum spacing requirements. C1063 specifies that wood framing for exterior lath shall not exceed 16 inches on center for most expanded metal lath applications, though 24-inch spacing may be permitted with heavier lath weights meeting the standard's minimum weight thresholds (generally 3.4 lb/yd² for horizontal applications and 2.5 lb/yd² for vertical).
2. Weather-resistant barrier (WRB) installation
C1063 requires that a weather-resistant barrier — compliant with ICC International Building Code Section 1404 requirements — be installed over the structural sheathing before lath is applied on exterior assemblies. The WRB provides a drainage plane and secondary moisture barrier independent of the stucco itself.
3. Lath selection and orientation
Lath must be installed with the long dimension perpendicular to the framing members. For expanded metal lath, the standard specifies that the diamond mesh cups must face upward to enhance plaster keying. Vertical laps between lath sheets must be made on stud lines; horizontal laps require a minimum 1-inch overlap at all points.
4. Fastener schedules
Fasteners must penetrate structural framing by a minimum depth specified in the standard — typically 1 inch into wood framing. Fastener spacing along each framing member is set at 6 inches on center for most applications. The use of undersized, incorrect-gauge, or inadequately penetrating fasteners is among the most commonly cited C1063 deficiencies identified during building inspection.
5. Corner and transition detailing
Cornerite (corner reinforcement strip), casing beads, control joints, and expansion screed must be installed per C1063's dimensional and placement requirements before the scratch coat is applied. Control joints are required at intervals not exceeding 144 square feet in area and at any point where the substrate changes material.
6. Inspection hold point
In jurisdictions that adopt C1063 by reference — including those using the IBC or IRC — a lath inspection is typically a required hold point before plaster application begins. The inspection confirms fastener schedule compliance, WRB installation, and proper accessory placement.
Common scenarios
C1063 applies across a range of installation contexts encountered in both new construction and remediation work, all of which are represented in the stucco repair listings accessible through this resource.
- New exterior stucco on wood-framed residential construction: The most common application. Requires compliance with framing spacing, WRB, and metal lath weight requirements.
- Re-stucco over existing failed assemblies: When existing lath is removed to the structural substrate, C1063 governs the full reinstallation sequence for the new lath layer.
- Commercial tilt-up and masonry substrates: Furring systems are required when the structural surface exceeds flatness tolerances; C1063 provides the furring channel specifications for these conditions.
- Soffit applications: Rib lath or self-furring lath is required for horizontal overhead plaster surfaces; minimum lath weight increases to 3.4 lb/yd² per the standard's soffit provisions.
- Interior plaster bases: Where portland cement plaster is used in wet interior areas (commercial kitchens, locker rooms, pools), C1063 applies to the lath substrate even on interior vertical surfaces.
For an overview of how this standard fits into the broader stucco service sector, the how to use this stucco repair resource page describes the professional categories and scope of work addressed across the site.
Decision boundaries
Understanding when C1063 applies — and when adjacent standards govern instead — is essential for contractors, inspectors, and project owners.
| Condition | Applicable Standard |
|---|---|
| Lath and furring installation for portland cement plaster | ASTM C1063 |
| Portland cement plaster mix design and application | ASTM C926 |
| Gypsum plaster application (interior, non-portland) | ASTM C842 |
| Aggregate specifications for job-mixed plaster | ASTM C897 |
| Exterior cladding water-resistive barrier requirements | IBC Section 1403–1404 |
C1063 vs. local amendments: Many jurisdictions — including California (governed by the California Building Code, Title 24) — adopt C1063 by reference but impose additional requirements for seismic zones, including enhanced fastener schedules and supplemental shear transfer details. Local code amendments supersede the base C1063 standard where they are more restrictive.
C1063 vs. proprietary systems: Manufacturer-specified EIFS (Exterior Insulation and Finish Systems) and synthetic stucco assemblies are not governed by C1063. Those systems follow individual ICC Evaluation Service Reports (ICC-ES) and their own installation specifications. C1063 applies only to portland cement-based plaster base systems.
Inspection authority: The International Code Council publishes the model codes that reference C1063. Enforcement authority rests with local Authority Having Jurisdiction (AHJ) building departments. Disputes over C1063 compliance during construction are resolved through the AHJ's plan review and inspection process, not through ASTM directly.
References
- ASTM International – ASTM C1063-21 Standard Specification for Installation of Lathing and Furring
- ASTM International – ASTM C926 Application of Portland Cement-Based Plaster
- International Code Council – International Building Code (IBC)
- California Department of General Services – California Building Standards Code, Title 24
- ICC Evaluation Service (ICC-ES) – Evaluation Reports for Building Products