Non Metallic Plaster Bases (Lath) – ASTM Standards for Testing, Installation and Performance
Similar to metal based products, non metallic plaster bases are used in stucco as well as other applications that necessitate use of a lath. ASTM standards C 933, C 847, and C 1032 are material specifications for metal plaster bases (lath) that describe physical characteristics such as gauge, opening size, weight, wire diameter, and thickness. Since these specifications are not performance based, the characteristics don’t apply to a non metallic plaster base (lath) which is fabricated from a
material such as plastic, fiberglass, etc. and has different physical properties than metal in terms of strength, elongation, etc. As a result, a task group within the ASTM C 11 committee worked to develop performance based as well as installation standards for non metallic lath. To date, the following three standards have been published and are available through ASTM.
ASTM C 1764 - Standard Test Methods for Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications
ASTM C 1787 - Standard Specification for Installation of Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications,
ASTM C 1788 - Standard Specification for Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications
With regards to types of plaster bases used with Stucco, section 6.1 of the ASTM standard below recognizes stucco can be applied to metal plaster bases installed per ASTM C 1063 or non metallic plaster bases installed per ASTM C 1787.
ASTM C 926 – 17 Standard Specification for Application of Portland Cement-Based Plaster
As a collective group, the above standards provide methods of installation, test protocol and minimum performance criteria related to wind (transverse) load, plaster embedment, fastener pull through and vertical load. Being performance driven rather than material specifications, the standards can be applied to all types of nonmetallic plaster base regardless of material composition.