System Overview:
The Western One-Pass® System is a code-recognized exterior stucco wall assembly utilizing Western One-Pass cement plaster in conjunction with approved weather-resistive barriers, metal lath, and compatible finish systems.

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Recognized under IAPMO UES ER-382, the system is uniquely formulated to function across multiple stucco assembly types, including one-coat, conventional scratch-and-brown, and monolithic cement plaster applications up to 7/8-inch thickness where permitted.

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Unlike traditional plaster systems limited to a single application method, the Western One-Pass System provides a universal exterior plaster solution adaptable to commercial, custom residential, and residential construction.

The system may incorporate the optional Crack Resistant System (CRS) and may be configured with fire-resistance-rated and NFPA 285-compliant wall assemblies in accordance with ER-382.

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System Intent and Performance:
The Western One-Pass System is engineered to:

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• Provide a cementitious basecoat application ranging from 3/8-inch minimum to 7/8-inch maximum thickness in accordance with ER-382 and approved lath configurations.

• Function as a one-coat stucco system when applied at 3/8-inch to 1/2-inch thickness over approved lath assemblies.

• Function as a conventional scratch-and-brown stucco system when applied in multiple lifts.

• Permit monolithic cement plaster applications up to 7/8-inch thickness where approved by ER-382.

• Comply with IAPMO UES ER-382 as a code-recognized exterior plaster assembly.

• Integrate with a range of architectural finish systems, including cementitious and acrylic coatings.

• Incorporate optional performance-enhancing components, including the Crack Resistant System (CRS) and Premium Acrylic Finish systems.

• Provide multiple fire-resistance-rated wall assemblies in accordance with ER-382.

• Allow NFPA 285-compliant wall configurations when constructed in accordance with approved assemblies under ER-382.

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When configured with the Crack Resistant System (CRS), the assembly incorporates a reinforced basecoat layer with embedded alkali-resistant mesh designed to enhance crack resistance characteristics and surface durability.

The Western One-Pass System is not structural and does not eliminate cracking resulting from structural movement.

System Components:
Basecoat:

• Western One-Pass (factory premixed, fiber-reinforced cement plaster).

• Minimum thickness: 3/8-inch over approved lath assemblies.

• Maximum thickness: Up to 7/8-inch in accordance with ER-382 and approved lath configurations.

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Weather-Resistive Barrier (WRB):

• Code-approved weather-resistive barrier installed in accordance with ER-382 and applicable building code requirements.

• Metal Lath & Accessories:

• Metal lath complying with ASTM C847.

• Installation in accordance with ASTM C1063.

• Control joints and expansion joints shall comply with project specifications and architectural plans prepared by the design authority or, in the absence of specific design direction, ASTM C1063 and ER-382 requirements.

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Exterior Finish Options:

• WBP Exterior Stucco Finish

• WBP Premium Acrylic Finish + PAF Primer

• Exterior finish coatings by approved listees recognized within IAPMO UES ER-382

• Premium Acrylic Finish assemblies requiring 7-, 10-, or 15-year warranty tiers shall incorporate PAF Primer in accordance with WBP installation requirements.

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Optional Enhancement: Crack-Resistant System (CRS):

• The Crack Resistant System (CRS) consists of BPS Armor CRS reinforcing basecoat and alkali-resistant fiberglass mesh installed at a minimum 1/16-inch embedment thickness.

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When incorporated into the Western One-Pass System, CRS elevates the assembly to the reinforced warranty tier in accordance with the warranty schedule. CRS enhances crack resistance performance but is not structural reinforcement.

Typical System Configuration:
The Western One-Pass System may be configured in multiple assembly types in accordance with ER-382:

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One-Coat Configuration:

• Approved structural substrate.

• Code-compliant weather-resistive barrier.

• Self-furred metal lath mechanically fastened in accordance with ASTM C1063.

• Western One-Pass applied at 3/8-inch to 1/2-inch thickness.

• Optional Crack Resistant System (CRS), when specified.

• Selected exterior finish coating.

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Conventional Scratch-and-Brown Configuration:

• Approved structural substrate.

• Code-compliant weather-resistive barrier.

• Metal lath installed in accordance with ASTM C1063.

• Western One-Pass scratch coat (minimum 3/8-inch).

• Western One-Pass brown coat (minimum 3/8-inch).

• Scratch & Double Back Method allowed (where the brown coat is applied shortly after the scratch coat, specifically when the latter has obtained sufficient rigidity).

• Optional CRS.

• Selected exterior finish.

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Monolithic Configuration:

• Approved structural substrate.

• Code-compliant weather-resistive barrier.

• Approved lath configuration per ER-382.

• Western One-Pass applied up to 7/8-inch thickness in a single application where permitted.

• Optional CRS.

• Selected exterior finish.

• Continuous insulation boards, where permitted under ER-382, may be incorporated within the assembly.

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Substrate Requirements:
Substrates shall comply with ER-382 and applicable building codes. Permitted substrates under ER-382 include walls of:

• Concrete

• Masonry

• Wood structural panel wall sheathing

• Fiberboard

• Light-frame construction covered with gypsum board

• Foam plastic insulation board

• Mineral wool insulation board

• Insulated concrete forms (ICFs)

• Similar approved substrates in accordance with ER-382

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Light-frame wall assemblies shall utilize wood studs with a minimum specific gravity of 0.50 or minimum 0.035-inch-thick (No. 20 gage) steel studs spaced a maximum of 24 inches on center.
Application of cement plaster shall be performed over substrates prepared in accordance with Section 3.2.3 of ER-382.
Substrates shall be structurally sound, properly braced, and free of conditions that may adversely affect system performance.

 

Environmental Conditions:
Components shall not be installed when surface or ambient temperatures are below 40°F (4.4°C) or above 100°F (38°C).
All cementitious components require a minimum of forty-eight (48) hours moist curing. Extended curing may be required under conditions of heat, wind, or low humidity.
Protect installed materials from freezing, rapid drying, or inclement weather until adequately cured.

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System Limitations:
The Western One-Pass System:

Is not structural.

• Does not eliminate cracking caused by structural movement.

• Requires proper control joint placement in accordance with ASTM C1063 or as specified by the project designer or architectural specification.

• Must be installed in accordance with ER-382 and WBP installation requirements.

• Requires installation by qualified applicators.

• System performance is dependent upon compliance with WBP installation guidelines and integration within approved stucco assemblies.

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Code and Standards:
The Western One-Pass System is recognized and evaluated under:​

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• IAPMO UES ER-382

• 2024, 2021, 2018 & 2015 International Building Code (IBC)

• 2024, 2021, 2018 & 2015 International Residential Code (IRC)

• 2025 & 2022 California Building Code (CBC)

• 2023 Florida Building Code (FBC)

• Applicable ASTM Standards:

• ASTM C926 — Application of Portland Cement-Based Plaster

• ASTM C1063 — Installation of Lathing and Furring to Receive Portland Cement-Based Plaster

• ASTM C847 — Metal Lath

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System Positioning:
The Western One-Pass System provides a universal, code-recognized exterior plaster solution capable of functioning across one-coat, conventional, and monolithic stucco assemblies within a single evaluated platform. By combining thickness versatility (3/8" to 7/8"), third-party evaluation under ER-382, fire-resistance-rated assembly options, NFPA 285 compliance capability, and integration with the Crack Resistant System (CRS), Western One-Pass offers a consolidated exterior plaster approach adaptable to commercial, custom residential, and residential construction. Through proper system configuration, the assembly may be tailored to meet project-specific objectives related to durability, crack resistance, fire performance, and extended warranty coverage while maintaining full compliance with ER-382.

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Warranty Schedule Matrix:
The warranty schedule matrix is based on finish configuration and incorporation of the Crack Resistant System (CRS). Warranty duration is dependent upon compliance with WBP installation requirements and proper integration of system components as defined in this Technical Data Sheet and ER-382. Western One-Pass basecoat assemblies are classified within the premium basecoat tier. Refer to the current Western Blended Products Warranty Schedule for specific configuration requirements and available warranty terms.