NOTE This standard governs the materials, lath and furring, accessories, mixing, application, and curing of portland cement-based plaster (stucco) for exterior cladding and interior finish. (1.1)

NOTE Portland cement plaster is a field-applied cementitious cladding built up in successive coats over a rigid base. Its weather performance depends less on the plaster itself than on the assembly behind it: the weather-resistive barrier, the drainage plane, the lath attachment, and the accessories that terminate, drain, and relieve the cladding. This standard treats the stucco as one layer of a coordinated wall assembly and binds the decisions that most often drive moisture and cracking claims. (1.2)

NOTE Stucco is a reservoir cladding that absorbs and stores water; it is not a barrier system, and the assembly behind it must be designed to drain. (1.3)

NOTE The three coat-system families covered here are three-coat hard-coat, two-coat over rigid substrates, and one-coat fiber-reinforced proprietary systems. (1.4)

NOTE Three-coat systems consist of a scratch coat, a brown coat, and a finish coat applied over metal or fiber-cement lath, and are the default for cladding over framed walls. (1.4.1)

NOTE Two-coat systems consist of a basecoat (combined scratch and brown) and a finish coat applied directly over a rigid, absorptive substrate such as concrete or concrete masonry. (1.4.2)

NOTE One-coat systems are proprietary factory-blended fiber-reinforced basecoats applied at nominal 3/8 in. thickness in a single pass, followed by a finish coat, and are evaluated under a product evaluation report rather than ASTM C926 coat thicknesses. (1.4.3)

NOTE The following are outside this standard and are governed elsewhere. (1.5)

NOTE Coordination with adjacent assemblies is required where stucco terminates against other work. (1.6)

NOTE Sealant joints at casing beads, control joints, and penetrations shall be specified and detailed under Joint Sealants. (1.6.1)

NOTE Cold-formed steel stud framing that receives lath shall comply with Cold Formed Metal Framing for gauge, spacing, and deflection limits. (1.6.2)

NOTE Thermal insulation within the wall cavity behind stucco shall be specified under Building Thermal Insulation. (1.6.3)

NOTE Materials, lath and furring, accessories, mixing, application, and curing shall comply with the latest adopted edition of each of the following unless a specific edition is cited or an adopted building code mandates a particular edition. (2.1)

NOTE Plastering quality depends on applicator skill, controlled mixes, and disciplined curing far more than on material selection alone, so qualification and mock-up requirements carry real weight. (4.1)

NOTE Single-source responsibility reduces the interface risk between basecoat, finish, and accessories. (4.2)

NOTE Field quality control verifies that the as-built assembly matches the approved mock-up. (4.3)

NOTE Portland cement plaster cures by hydration, so application temperature and moisture control directly govern strength and crack resistance. (5.1)

NOTE The weather-resistive barrier requirement behind stucco varies by climate zone, and getting it wrong is a common source of code non-compliance. (5.2)

NOTE Coat thickness and the number of coats are the backbone of stucco performance; thin or skipped coats are a direct cause of cracking and water intrusion. (6.1)

NOTE Curing intervals between coats allow shrinkage to occur before the next coat locks the surface, which is why fast-tracking the schedule causes cracking claims. (6.2)

NOTE Material selection binds the mix chemistry; loose specifications let contractors over-sand weak coats or under-lime brittle coats. (7.1)

NOTE The basecoat mix shall be either a factory pre-blended bagged product or job-mixed to the cement-lime-aggregate proportions of ASTM C926 Table 1 for the selected base. (7.2.1)

NOTE The finish coat type shall be selected for the project appearance, exposure, and recoating intent. (7.3.1)

NOTE The finish texture shall be specified by name and confirmed by an approved sample panel; texture names alone without a sample shall not be relied upon for acceptance. (7.3.5)

NOTE Water-repellent admixture improves the cladding's resistance to absorption but is not a substitute for the drainage plane. (7.4)

NOTE The plaster base anchors the stucco; lath type and attachment determine whether the cladding deflects and cracks under load. (8.1)

NOTE Lath and furring installation shall comply with ASTM C1063, which governs the fastener schedule, stud spacing limits, and accessory installation. (8.2)

NOTE Stud spacing limits imposed by ASTM C1063 prevent over-deflection of the lath and the basecoat cracking that follows. (8.3)

NOTE Accessories terminate, drain, and relieve the cladding; their selection and placement are where most stucco moisture defects originate. (9.1)

NOTE A weep screed is the drainage and termination accessory at the base of an exterior stucco wall over framing; omitting or blocking it is among the leading causes of moisture intrusion claims. (9.2.1)

NOTE Control joints relieve drying shrinkage and thermal movement; without them, panel cracking is not a defect but an inevitability. (9.3.1)

NOTE Corner beads reinforce and straighten outside corners; casing beads form a clean, sealable termination where stucco meets dissimilar materials. (9.4.1)

NOTE Application sequence and workmanship determine whether the coats bond and cure as a monolithic cladding. (10.1)

NOTE Application over different substrates requires substrate-specific preparation. (10.2)

NOTE Crack control and continuity at penetrations limit the entry points for water. (10.3)

NOTE Cementitious materials lose performance when exposed to moisture or contamination before use. (11.1)

NOTE The warranty allocates responsibility for early-life cracking and water intrusion to the installer and, where applicable, the system manufacturer. (12.1)

NOTE Stucco repairs depend on matching the original color, texture, and source, so a small reserve of finish material and an accurate record prevent visible patches. (13.1)