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Fluid/Liquid-Applied Air & Moisture Barriers

A quality air and vapor barrier membrane helps create an efficient exterior wall system by preventing air, and any accompanying moisture, from infiltrating the structure’s interior. Air vapor barriers come in two forms with various applications: fluid and sheet-applied air barriers.

Some of the factors that architects and builders often consider when deciding between sheet-applied and fluid-applied weather barriers include:

  • Managing water vapor with an air barrier
  • Building geometry
  • Substrate materials
  • Project conditions
  • Weather conditions
  • Climate
  • Time

Read on to learn more about liquid-applied air barrier systems, like Sto Fluid-Applied Air and Moisture Barriers and StoGuard Detail Components, and the benefits and concerns of these systems.

Fluid-Applied Membrane Air Barriers

A fluid-applied membrane air barrier is a monolithic coating that bonds to the exterior sheathing without fasteners. A high-performing fluid-applied vapor barrier contributes to energy-efficient, durable, and healthy residential, commercial, and institutional environments.

The Benefits of Fluid-Applied Air Barriers

Fluid-applied air and water-resistive barriers provide many benefits that save money and time and help preserve the integrity and health of a building:

Allows for Complex Detailing

A liquid air barrier efficiently adheres to and waterproofs various wall conditions (e.g., penetrations, fasteners, repair locations, and detail wall openings) and conforms to uneven substrates. In contrast, sheet-applied air and moisture barriers require cutting, folding, lapping, and sealing.

A liquid vapor barrier quickly and easily adapts to complex architectural substrate geometry.

Fast Application

A qualified installer can quickly spray or roll the air and water-resistive barrier membrane onto the wall substrate to save money and time.

A spray-applied vapor barrier does not require a primer, which saves even more time.

Air Barrier

A fluid-applied water resistive barrier (WRB) stops air leakage, reduces energy costs and condensation, and improves occupant comfort.

Moisture Barrier

A liquid-applied vapor barrier creates a seamless moisture barrier by minimizing installation errors that can cause tears, holes, or lap joints.

Wind Barrier

A liquid-applied WRB provides structural and full adherence, for rigidity and stability against severe wind events.


A liquid moisture barrier will not lose its effectiveness when exposed to outdoor elements during and after construction. Checking with the manufacturer’s recommendation for length of exposure.

Lessens Repairs

A fluid-applied moisture barrier membrane protects the rough openings and sheathing from weather damage during and after construction, which lessens replacement or repair expenses.


Safe to use, V.O.C. compliant water-based air and vapor barriers are easily cleaned up.

Rainwater Barrier

Liquid-applied barriers for pressure-moderated or pressure-equalized wall design will reduce the risk of rainwater penetration through the wall assembly.

Problems with Fluid-Applied Air Barriers

Fluid-applied air barriers require a professional-quality application and dry conditions to ensure their performance.

Requires Skilled Labor

A fluid-applied air and moisture barrier typically requires experienced and professional installers capable of applying the barrier, as they need to use a specialized spray gun, at a constant, steady rate to ensure consistent thickness and adequate coverage at detail interfaces.

The air and barrier’s performance depends on hiring qualified and skilled installers that carefully follow the manufacturer’s instructions, which is a complex task with today’s shortage of skilled labor.

Sto Gold Coat, Sto AirSeal, Sto VaporSeal do not have to be spray applied. They can also be applied with a roller. Therefore, the skill level required for application is not a problem. Sto ExtraSeal, in particular, is a trowel-applied product.

Sto Detail Components and Fluid-Applied Air and Moisture Barriers

The StoGuard® System includes vapor permeable air barrier or impermeable fluid-applied membranes, depending on climate and wall design: Sto Gold Coat®, Sto ExtraSeal®, Sto AirSeal®, and Sto VaporSeal™ – all function as waterproof air barriers when used with StoGuard Detail Components.

StoGuard Detail Components

StoGuard detail components, in combination with Sto fluid-applied membranes, provide durable, continuous water and air-resistive barriers at critical areas like movement joints, penetrations, substrate transitions, transitions to rough openings, roofing, and below-grade air barriers. Builders typically apply Sto Detail components and then overcoat them with the fluid-applied membrane.

Sto RapidGuard™

Single-component, vapor-permeable Sto RapidGuard® is an above-grade wall construction multi-use air barrier and waterproof material. Easy-to-use, flexible, and fast-drying Sto RapidGuard® provides high-quality air and moisture protection on CMU, concrete, brick masonry, gypsum sheathing, wood, galvanized metal, and cement-based sheathings.

Applications: seal rough openings, seams, sheathing joints, cracks, and transitions.

StoGuard® Conformable Membrane

Self-adhered StoGuard Conformable Membrane (in 4-inch, 6-inch, and 9-inch widths) features an aggressive no-primer adhesive and a facing membrane that offers 1470 percent elongation. The high-elongation facer membrane readily conforms to complex shapes found on the building enclosure. Only apply StoGuard Conformable Membrane at a temperature above 20°F.

Applications: Sheathing joints and corners, dynamic joints, seams, static joints, penetrations, and flashings and rough opening protections.

StoGuard® Fabric

Tough StoGuard® Fabric (in 4-inch, 6-inch, and 9-inch widths) saturates with Sto Gold Coat®, Sto AirSeal®, or Sto VaporSeal® to produce a flexible, waterproof flashing material and sheathing joint treatment.

Applications: Penetrations, sheathing joints and corners, flashing, and rough opening protections.

StoGuard® RediCorner

Preformed StoGuard® RediCorner fabric installs quickly on the rough openings of a sheathing joint’s inside and outside corners. Builders can use it as part of the StoGuard® assembly with either Sto Gold Coat®, StoGuard® VaporSeal™, or Sto EmeraldCoat®.

Sto Gold Fill®

Ready-mixed, trowel-applied Sto Gold Fill® embeds StoGuard Mesh to create a waterproof composite material.

Applications: Penetrations, rough opening protections, and sheathing joints and corners.

StoGuard® Mesh

Builders can use self-adhesive, glass fiber, StoGuard® Mesh with Sto Gold Fill®, Available in 4.25- and 9.5-inch widths.

Sto Detail Mesh

Builders can use coated glass fiber Sto Detail Mesh with Sto Gold Fill to treat sheathing joints and flash rough openings.

Sto Fluid-Applied Air and Moisture Barriers

Sto Gold Coat® Permeable Vapor Barrier

Vapor-permeable, ready-mixed, and flexible Sto Gold Coat® is a flexible fluid-applied membrane designed for installation on most commonly used substrates. It can be used as part of StoTherm, StoPowerwall, StoQuik and StoVentec wall systems, and is suitable for use behind most exterior claddings including rainscreen, metal, wood, stone, brick, and masonry. It applies with a roller or sprays directly to vertical above-grade wall sheathing and concrete masonry, and functions as a waterproof air barrier when used with StoGuard Detail Components.

Sto ExtraSeal® Vapor Permeable Membrane

Vapor-permeable, trowel or spray-applied Sto ExtraSeal® is a portland cement-based moisture and air-resistant barrier that is applied over prepared above-grade concrete and concrete masonry (CMU) walls beneath StoPowerwall® and other Sto-listed ASTM C926 stucco brown coats. In addition, it provides substrate water and air leakage resistance.

Sto AirSeal®

Sto AirSeal® is a flexible, fluid-applied membrane designed for installation to commonly used substrates beneath most exterior claddings. It can be used as part of StoTherm, StoPowerwall, StoQuik and StoVentec wall systems, and is suitable for use behind most exterior claddings including rainscreen, metal, wood, stone, brick, and masonry. Sto AirSeal® features 500% elongation and meets ASTM C1305 Low Temperature Crack Bridging requirements. The unique rheology of Sto AirSeal is optimized for high-build installation.

Sto VaporSeal™

Sto VaporSeal® is a Class 1 Vapor Retarder designed for spray or roller installation to most commonly used substrates. It can be used as part of StoTherm, StoPowerwall, StoQuik and StoVentec wall systems, and is suitable for use behind most exterior claddings including rainscreen, metal, wood, stone, brick, and masonry. Sto VaporSeal® features 500% elongation and meets requirements of ASTM C1305.

Why Choose Sto Fluid-Applied Air and Moisture Barriers Products?

Sto’s roller or spray-applied family of fluid/liquid-applied air barrier products give architects and builders a superior solution to their weather barrier design and application challenges. Our easy-to-apply products save money and time during the application process and maintain their integrity for the builder’s lifetime.

Contact our Sto professionals today for more on fluid-applied air and moisture barriers and detail components.

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