by Jim Moody on May 5, 2016

Pros and Cons of 3 Cement Board Wall Systems

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The metal lath/scratch coat method of preparing a surface for masonry has traditionally been the go-to for many installers. Recently, however, manufacturers have been developing complete wall solutions using cement board. For many applications, these engineered wall systems are faster, easier, and cleaner than traditional lath methods.

As with any process, there are benefits as well as drawbacks to introducing cement board to the building envelope as part of a thin brick or stone veneer design. Below, we explore the pros and cons of three of these exterior cement board wall systems using the PermaBase product from our partners at National Gypsum Company

1. Cement Board Masonry Veneer Wall System (CBMV)

CBMV offers a complete solution for installation of adhered veneers in residential and low-rise commercial applications. For exteriors, CBMV allows the installer to incorporate a water-management system with manufactured or natural stone and thin brick veneers.

Benefits/Pros

  • Engineered system that allows a faster installation while providing superior quality control
  • Performance and longevity are increased through the use of polymer modified adhesive mortars (designed for hanging materials) rather than S&N mortars (developed for stacking materials)
  • Extremely durable with an increased resistance to impact and inclement weather
  • Approved for use in ASTM C 1780; additionally, cement board is cited as an approved substrate for this system by the Masonry Veneer Manufacturers Association
  • Appropriate for all climates and resists the growth of mold and mildew
  • Faster, easier and cleaner than traditional metal lath/scratch coat method
  • IBC/IRC Compliant. Meets ASTM C 1325
  • PermaBase is approved as a substrate for direct applied finishes, tile, stone, and thin brick in exterior applications, as outlined in ICC-ES Evaluation Report ESR-1510

 

Limitations/Cons

  • Sheathing selection and installation varies according to type of wall construction
  • Code-approved water/air resistive barrier must be installed to protect the cavity

2. Cement Board Stucco Wall System (CBSS)

As with CBMV, CBSS is ideal for residential and low-rise commercial applications. CBSS provides a drainage system to help prevent water from penetrating behind cladding in framed construction. It complies with ASTM D 226, protecting approved sheathings and structural components and helping to evacuate incidental water. 

 Benefits/Pros

  • Appropriate for all climates and resists the growth of mold and mildew
  • Extremely durable with an increased resistance to impact and inclement weather
  • Acrylic polymers provide more resistance to fading, cracking and peeling
  • Engineered system that allows a faster installation while providing superior quality control
  • 15-year exterior warranty—the industry’s best

 

Limitations/Cons

  • Follow finish material manufacturer’s instructions for proper installation
  • Treat joints in PermaBase with mesh tape and base coat
  • Thin veneer construction can reveal planar irregularities in framing
  • Minor cracking at joints may become visible in finished exterior surfaces.
  • When exterior finishes are applied directly to PermaBase: Reinforcing mesh must be embedded in the basecoat (consult exterior finish manufacturer for additional installation requirements)
  • Conventional Portland Cement plaster systems: self-furring metal lath must be used over PermaBase and fastened to studs
  • Code-approved water/air resistive barrier must first be installed to protect the cavity

 

3. Continuous Insulation 

Continuous insulation offers a complete engineered solution for required structural performance. Including PermaBase as a component in this system reinforces the building and provides the ability to incorporate an effective water-management system.

 Benefits/Pros

  • Engineered system that allows a faster installation while providing superior quality control
  • Helps mitigate the loss of heat and/or air conditioning by insulating the studs (reduces thermal bridging)
  • Helps eliminate leakage of air and moisture
  • Appropriate for all climates and resists the growth of mold and mildew
  • Provides added dimensional stability
  • Helps prevent compromising of Water/Air Resistive Barrier (WRB) as assembly components shift
  • 15-year exterior warranty—the industry’s best

 

Limitations/Cons

  • Sheathing selection and installation varies according to type of wall construction
  • Code-approved water/air resistive barrier must first be installed to protect the cavity

 

General Code Requirements (Check to verify requirements in your area)

There are some basic code requirements when installing movement joints designed to accommodate the expansion and contraction of long walls.

Such vertical movement joints are typically spaced at maximum 20' - 25' O.C. horizontally, at interior corners, at changes in wall plane, and where thin stone contacts different materials or wall systems.  

The Masonry Code for thin adhered veneer, Par. 12.3.2.2 states: "Wall area limitations - Height, length and area of adhered masonry veneer shall not be limited EXCEPT as required to control restrained differential movement stresses between veneer and backing." The movement joint is simply an uninterrupted, empty, vertical joint (3/8" wide) filled with backer rod and sealant.

 

These pros and cons are a great guide to get started, but specifications and details on how to design and construct individual systems should be obtained from the adhering material or veneer manufacturer. For more information on incorporating PermaBase into exterior cement board wall systems, visit permabase.com/exteriors or contact us at Trowel Trades Supply.

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