For the last three installments in this continuing series (parts four through six), we discussed gypsum-based sheathing. Prior to that, we discussed wood-based sheathing and the uses, purpose and environmental characteristics of sheathing materials. This month, we'll take a look at cement-based sheathing.

sheathing materials. This month, we'll take a look at cement-based sheathing.

Essentially, there are two types of cement-based sheathing:

• Cement
  
  
• Fiber-cement

Cement-based

Made from aggregated Portland cement reinforced with glass-fiber mesh on both sides of a cement-board panel, cement-based sheathing is most effective where moisture resistance is the top priority. Considered "water-durable," cement-based sheathing is highly resistant to moisture damage and will not rot, delaminate, bend or warp. This impervious-to-moisture aspect of cement-based sheathing makes it an ideal substrate for EIFS, ceramic tile, thin brick and more.

Being incombustible, cement-based sheathing also offers fire-resistance/performance and is suitable for both combustible (residential) and non-combustible (commercial) applications.

Fiber-cement based

A reinforced cement-board panel also, fiber-cement is denser than standard cement-board panels and has water durability. Added to the aggregated Portland cement is cellulose for reinforcing.

Hybrid

Euroform Products Ltd. offers through its exclusive distributor Architectural Products Inc., of Lincoln, R.I., (www.architecturalproducts.com) a type of fiber-cement sheathing the company calls Versaroc Cement Bonded Particle Board. Light gray in color, Versaroc is composed of mineralized wood particles and Portland cement. This combination of wood and cement combines the strength and workability of wood with the durability and resistance values of cement that include:

• Fire-resistance
  
  
• Moisture-resistance
  
  
• Resistance to rot, vermin, decay and impact

Flat and smooth on both surfaces, Versaroc is composed of:

• 71 percent Portland cement
  
  
• 19 percent mineralized wood fiber
  
  
• 9 percent water
  
  
• 1 percent bonding chemicals

This hybrid combination contains no formaldehyde, volatile organic compounds and is non-toxic. Because of its mass and density, it has strong sound attenuation (airborne noise reduction) abilities. During the manufacturing process, the wood particles are mineralized with non-toxic chemical agents to provide fire resistance. Then, they are added to the Portland cement matrix to provide the panels with strength and flexibility.

Versaroc is offered in two panel sizes:

• 4 feet wide by 8 feet long
  
  
• 4 feet wide by 10 feet long

In thicknesses of 5/16, 3/8 and 1/2 inch, the edges are square. The 3/4-, 7/8-, 11⁄8-, 11⁄4- and 11⁄2-inch thick panels used as sub-flooring, have a tongue-and-groove edge, and are available with a primer/sealer. Versaroc can be used for both interior and exterior applications for floors, walls, ceilings and as a general-purpose building panel. Dimensionally stable, its surfaces are non-directional and can be:

• Sawn
  
  
• Planed
  
  
• Sanded
  
  
• Drilled
  
  
• Routed
  
  
• Nailed and/or screwed

Without a sealant, it remains stable and will not delaminate when immersed in water ("thickness-swell" test). Panel weight varies from 2 pounds per square foot to 6.25 pounds per square foot depending on panel thickness. With a density of 77 pounds per cubic-foot, its acoustical performance is in a range of 30 to 35 sound transmission co-efficient. Designated as a non-combustible building material (per ASTM E136), it has surface burning characteristics of:

• Flame Spread: 0
  
  •
• Smoke Developed: 0

Versaroc can be installed as a substrate material over wood or metal framing. Countersunk, self-tapping screws are used for light gauge metal framing and screws, nails or staples for wood framing. With L/360 as the allowable "Limiting Deflection," Versaroc can withstand wind-loads ranging from 75 to 150 mph:

Thickness @16"oc @24"oc
3/8" 120 mph 75 mph
1/2" 150 mph 90 mph
3/4" 150 mph 150 mph

It is useful as a substrate material for modular or on-site construction and installs much like fire-treated wood sheathing. Being resistant to water/the freeze-thaw cycle/impact/sound transmission/mold/fungus/termites and vermin, Versaroc Cement Bonded Particleboard possesses all that is desirable in a cement-based sheathing product.

Other cement-based sheathing products include:

• Hardibacker (jameshardie.com)
  
  
• PermaBase (nationalgypsum.com)
  
  
• HUILON Fiber Cement Board (qshuilong.en.alibaba.com)

In part eight, we'll conclude this series all about sheathing with a look at the fourth type of sheathing product: plastic/foam-based.