Architectural Record BE - Building Enclosure

Fluid Applied Air/Moisture Barriers for Moisture Control and Mold Prevention in Wall Construction

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Advertorial course provided by Sto Corp
Continuing Education

Learning Objectives - After this course, you should be able to:

  1. Know the components of fluid applied air/moisture barriers
  2. Compare the advantages of fluid air/moisture barriers with building wraps and other moisture barriers
  3. Identify design considerations when incorporating fluid applied air/moisture barrier systems into wall assemblies


Fluid applied air/moisture barriers are effective and economical means of controlling moisture in wall assemblies. Moisture control assists in preventing mold growth in wall assemblies. Fluid applied air/moisture barriers also offer performance advantages over building wraps and traditional asphalt- impregnated felt or paper moisture barriers. They can be used in all types of wall construction over wood, gypsum and cement-based sheathings. They can also be used over prepared concrete and concrete masonry units. They generally consist of three components (Figures 1a and 1b on page 204):

  1. A spray- or trowel-appliedjoint treatment for filling sheathing joints, spotting fasteners, and protection of rough openings, corners and other changes of plane in sheathed wall construction.
  2. Areinforcing mesh or tape used in conjunction with the joint treatment to reinforce sheathing joints, corners, and changes of plane, and for repair of minor cracks in concrete or concrete masonry wall construction.
  3. Awaterproof coating applied by spray, roller or brush to prepared sheathing, concrete or concrete masonry wall surfaces.

When properly applied to sound supporting construction, these components function together as an air barrier and seamless moisture barrier in the wall assembly. Some of the advantages of a fluid applied air/moisture barrier include:

Effectively blocks air leakage
  • Increases occupant comfort
  • Reduces energy costs by reducing heating and cooling loads
  • Reduces risk of condensation caused by air leaks through the wall construction
Seamless moisture barrier
  • no tears, holes, or lap joints that can compromise performance in service
  • reduces risk of installation errors
Protects sheathing and rough openings from weather damage during and after construction
  • minimizes risk of weather damage to sheathing and associated repair or replacement costs
Simple installation procedures
  • No special tools or skills required; reduces labor costs
  • Does not tear or lose its effectiveness with exposure to weather during construction or while in service
Structural/fully adhered
  • Rigid and stable under air pressure loads, does not tear or blow off the wall with wind
Distinct colors
  • Facilitates job site inspection and quality control
Water based
  • Safe to use, easy clean-up, VOC-compliant
Provides opportunity for pressure equalized or pressure moderated wall design
  • Minimizes risk of rain water penetration through wall assembly
Doubles as air barrier and moisture barrier in wall assembly
  • Efficient use of materials


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Originally published in Architectural Record.