U-STUCCO™ XPX

High-Performance Insulating Fire-Resistant Coating for Next-Generation Wall Systems

Product Description

U-STUCCO™ XPX is a factory-blended, ultra-lightweight, fiber-reinforced, Portland cement–based mineral plaster / stucco engineered to deliver integrated fire resistance, thermal insulation, water resistance, vapor permeability, acoustic performance, and long-term durability as a high-performance mineral envelope layer. Designed for both new construction and retrofit applications, U-STUCCO™ XPX is suitable for use over ICF, ICCF, SIP, Rockwool assemblies, AAC, CMU, tilt-up and precast concrete, 3D-printed concrete, and steel or wood frame wall systemswith fiber cement board sheathing.

Conforming to ASTM C926 for Portland cement plaster application, XPX may serve as a scratch coat, brown coat, top coat, or interior plaster when sealed with water-based sealant or paint. It also functions as a high-performance base coat compatible with third-party cementitious or acrylic finish systems, providing flexibility in façade design and specification.

Compatible Substrates & Wall Systems

Suitable for new construction and renovation projects over:

ICF, ICCF, SIP, Rockwool, AAC, CMU, Tilt-Up Concrete, Precast, 3D-Printed Concrete, Steel & Wood Frame Systems w/ Fiber Cement Board Sheathing

Recommended Uses

• Fire-resistant exterior wall systems

• ICF & SIP building envelopes

• Steel fireproofing coating

• EPS / XPS/ Poly Iso fire protection layer

• Retrofit fire-resistant coating over existing stucco

Composition Standards

ASTM C150 – Portland Cement

ASTM C330 / C332 – Lightweight Aggregates

ASTM C926 – Application of Portland Cement–Based Plaster

Fire Performance Standards

U-STUCCO™ XPX is a non-combustible, mineral-based plaster that forms a continuous fire-resistant barrier when applied at ½ inch thickness or greater. When incorporated into properly designed wall assemblies, XPX supports compliance with NFPA 285 and related façade fire propagation standards. Fire performance aligns with:

ASTM E84 – Surface Burning Characteristics

ASTM E136 – Non-Combustibility

NFPA 285 – Multi-story wall assembly fire propagation

ISO 22899-1 – Jet Fire (Oil & Gas)

AS 5113 / AS 1530 – Australian façade fire testing

At 1-inch thickness, testing has demonstrated resistance to extreme heat exposure up to 3000°F (≈1650°C) for more than 2 hours, depending on assembly configuration.

Thermal Performance

XPX delivers R-2.2 per inch thermal resistance (ASTM C518), contributing continuous exterior insulation while helping reduce thermal bridging at framing members, fasteners, structural transitions, and attachment points. When used with EPS, XPS, ICF, or mineral wool insulation systems, XPX enhances overall wall assembly R-values and supports compliance with California Title 24 energy requirements. Its ultra-lightweight, fiber-reinforced formulation replaces traditional multi-coat scratch and brown systems and can be applied up to 1 inch in a single pass, improving construction efficiency while significantly reducing dead load on the structure.

Water Resistance & Vapor Permeability

The hydrophobic mineral formulation provides water resistance over AAC, CMU, ICF, ICCF, and masonry substrates while maintaining vapor permeability of 32 perms, allowing wall assemblies to resist bulk water intrusion while retaining drying capability. This balance supports long-term moisture durability without trapping vapor within the assembly.

Acoustic Performance

At 1-inch thickness, XPX provides sound absorption performance of up to 42 dB, contributing to airborne noise reduction in residential, multi-family, commercial, and institutional applications.

Mold / Mildew & Environmental Performance

The inorganic, VOC-free composition does not provide a nutrient source for mold or mildew, contributing to improved hygro-thermal stability and long-term durability in interior and exterior wall assemblies. XPX is composed of predominantly inorganic materials and incorporates post-consumer recycled content, supporting sustainable building practices.

Application Methods

Apply by hand trowel or mechanical plaster spray equipment.

Application Temperature

Ambient and substrate temperatures must be between +40°F (5°C) and +95°F (35°C) during application and curing. Avoid installation under extreme wind, freezing conditions, direct sunlight, or when temperatures are expected to fall below recommended limits during curing.

Substrate Preparation

All substrates must be structurally sound, clean, dry, and free of dust, dirt, mold, oil, grease, silicones, curing compounds, paint, or other contaminants that may impair adhesion. All loose, deteriorated, or poorly bonded material shall be removed prior to application.

Major cracks, voids, holes, or surface irregularities must be properly repaired and allowed to cure before applying U-STUCCO™ XPX. Highly porous or absorptive substrates, including concrete and masonry, should be pre-dampened with clean water to control suction and prevent premature moisture loss.

The product is designed to adhere directly to approved substrates to create a monolithic bond between the plaster and the substrate surface. Proper adhesion to the substrate is required to achieve the intended structural integrity and performance characteristics.

A code-compliant water-resistive barrier (WRB) shall be installed and properly flashed in accordance with applicable building codes and manufacturer requirements. Although U-STUCCO™ XPX is water-resistant and hydrophobic, it is not intended to function as the primary water-resistive barrier within the wall assembly.

Metal lath installations must comply with ASTM C1063 requirements and be securely fastened to the supporting structure.

U-STUCCO™ XPX shall not be applied directly over paper and metal lath assemblies. An exception is permitted when U-STUCCO™ XPX is installed over existing cured stucco surfaces as part of a retrofit fire-resistant coating system, provided the existing substrate is sound, clean, and properly prepared.

Highly absorptive, dense, smooth, or non-absorptive substrates may require surface conditioning, bonding preparation, or project-specific evaluation. For unusual substrate conditions, contact U-STUCCO™ USA Technical Support.

All substrate preparation and installation must comply with applicable building codes, ASTM standards, and U-STUCCO™ installation guidelines.

Limitations

• Ambient or substrate temperature is below 40°F (5°C) or above 100°F (38°C)

• Substrate is frozen, excessively hot, or saturated with water

• Rain, freezing temperatures, or strong winds are expected during application or curing

Do not apply to frozen substrates or surfaces containing frost or ice.

Protect freshly applied material from rain, freezing conditions, rapid drying, and direct sunlight until adequately cured.

Only U-STUCCO™ USA approved additives may be used with this product. Do not add cement, lime, sand, paint, or other materials.

Always perform a job site mock-up or test area prior to full installation to verify compatibility, coverage, and finish appearance.

Wall assemblies incorporating U-STUCCO™ XPX must be designed in accordance with applicable building codes, ASTM standards, and project-specific fire performance requirements. The overall fire rating of the wall assembly depends on substrate configuration, insulation materials, building system, and installation method.

Mixing Instructions

Pour the entire U-STUCCO™ XPX 35.2 lb (16 kg) bag into a suitable mixing container. Add a minimum of 3.7 gallons (14 liters) of clean, cool potable water. If using a hose, allow the water to run briefly first to remove hot water from the line.

Mix mechanically using a plastering mixer only for approximately 5 minutes at low speed until a homogeneous, smooth consistency is achieved. Allow the mixture to rest for 1 minute, then re-mix for an additional 1 minute before application. Do not over-mix the material.

If the material appears too dry after the initial 5-minute mixing cycle, additional water may be gradually added to improve the consistency, but the total water ratio must never exceed 3.9 gallons (15 liters) per bag. Because U-STUCCO™ is hydrophobic, it does not absorb water as quickly as traditional stucco products, which is normal. Before adding additional water, allow the material 2–3 minutes to begin absorbing the initial water.

For true and consistent performance, the entire bag must be mixed at once. Never mix partial quantities such as half bags or small portions. Do not split a bag into multiple buckets. The full contents of each bag must be mixed together in a large plaster mixer using the specified water ratio.

The correct consistency should resemble whipped cream. When a trowel is dipped into the mixture and flipped upside down, the material should remain bonded to the trowel or drip very slowly.

For reference, see the mixing videos available on the U-STUCCO™ YouTube channel.

Application

Thoroughly dampen concrete and masonry substrates, if necessary, prior to applying U-STUCCO™ XPX. The material may be applied by hand trowel or plaster pump to a minimum thickness of approximately 1/2 inch (12 mm)and up to a maximum thickness of 1 inch (25 mm) in a single pass.

Using a trowel or plaster pump, apply U-STUCCO™ XPX to the properly prepared surface. Always float the material uniformly to create a consistent surface suitable for the application of a finish coat.

A sand or smooth finish may typically be achieved within 2 to 6 hours after application, depending on substrate type, application thickness, ambient temperature, and relative humidity. Finish timing may vary based on site conditions and installer technique.

Various surface textures may be achieved using different finishing techniques. Allow U-STUCCO™ XPX to dry thoroughly before applying acrylic primers, coatings, or finish systems.

Read the entire product label before using this product. All materials must be installed in compliance with local building codes, ASTM C926, ASTM C1063, and U-STUCCO™ USA specifications.

Finishing

U-STUCCO™ XPX may be integrally colored using mineral powder pigments (sold separately) added during the mixing process. If no pigments are added, the natural color of U-STUCCO™ is off-white.

Whether integrally colored or left in its natural color, all U-STUCCO™ surfaces must be sealed using a breathable, water-based sealer to enhance surface durability, water resistance, and long-term performance.

As an alternative to integral coloring, U-STUCCO™ may be painted using breathable, water-based paints or coatings specifically designed for mineral or cementitious substrates. Solvent-based coatings are not recommended.

Painting or sealing shall only be performed after the material has cured for a minimum of 7 days from the date of application, depending on ambient temperature, humidity, and substrate conditions.

Proper curing must be confirmed prior to the application of sealers or coatings to ensure optimal adhesion and long-term performance.

Coverage

Approximate coverage is based on uniform application thickness under ideal conditions with no material waste. 

35.2 lb (16 kg) Bag Coverage:

Working Time

U-STUCCO™ XPX provides an approximate working time of up to 60 minutes after mixing, depending on ambient temperature, relative humidity, substrate conditions, and job site environment. Higher temperatures and lower humidity levels may reduce working time. Mix only the amount of material that can be applied within this period.

Packaging

U-STUCCO™ XPX is supplied in moisture-resistant multi-layer bags.

Package Weight: 35.2 lb (16 kg) bags

Pallet Configuration: 40 bags per pallet

Container Capacity: 1,600 bags per 40-ft container

Storage Requirements: Pallets should be stored off the ground in a dry, covered location and protected from rain and moisture.

Storage temperature must be maintained above 40°F (5°C).

Health & Safety

U-STUCCO™ XPX may cause irritation to eyes and skin upon contact. Appropriate personal protective equipment (PPE), including dust masks, gloves, and eye protection, should be worn when handling or mixing the material.

In case of eye contact, flush immediately with clean water and seek medical attention if irritation persists. Wash exposed skin thoroughly with soap and water after handling the product.

For detailed information regarding safe handling, storage, and disposal, refer to the Safety Data Sheet (SDS).

Keep out of reach of children.

Quality Management

U-STUCCO™ Green Building Materials are manufactured under ISO 9001 quality management standards. Product performance and quality control are monitored in accordance with EN 998-1 requirements and verified through internal laboratory testing conducted by U-STUCCO™ USA, LLC.