In the last two parts of this on-going series all about sheathing, we've been discussing gypsum-based sheathing products. In part four, we discussed the two basic types of surface reinforced gypsum sheathing: paper-faced and glass-mat faced. We also discussed the newest entry into the gypsum-based sheathing category: gypsum/cellulose.

Last month, we took an in-depth look at USG's gypsum/cellulose, core-reinforced sheathing product Fiberock Aqua-Tough Sheathing. This month, we'll take a look at the newest products in paper- and glass-mat faced gypsum sheathing.

StructGuard TS

As an alternate to plywood and/or OSB, Temple-Inland introduced StructGuard TS-a gypsum-based sheathing product meant to compete directly with wood-based sheathing. The product utilizes Temple-Inland's TemShield anti-microbial mold protection system. Without limiting permeability, the faces are designed to resist moisture penetration and the enhanced mold-resistant core resists the development of mold and mildew. It was tested for resistance to:
  • Water absorption (less than 6 percent for both 1/2 and 5/8 inch thick per ASTM C473)
  • Water penetration (per ASTM E331)
  • Mold (per ASTM D 3273)
StructGuard meets the criteria that is recognized as a wall bracing material by model codes including: IRC (R702.3), IBC, UBC, SBC and NBC. Per ASTM 1396 and IRC R602.10.3, the sheathing product meets the acceptance criteria for structural gypsum sheathing and each panel indicates this fact with a printed stamp on its face.

When used as structural sheathing, the nailing pattern requires 4-inch spacing around the perimeter and 8-inch spacing in the field. It comes in two thicknesses of 1/2 and 5/8 inch (1.72 and 2.4 pounds per square foot, respectively) and has a thermal resistance (R-value) of 0.45 (1/2 inch) and 0.56 (5/8 inch). The 5/8-inch-thick panels are UL approved for fire-rated assemblies inclusive of fire-resistant sheathing (GA 254). Both sized-panels have a non-combustible gypsum core and their surface burning characteristics are as follows:
  • Fire spread: 15
  • Smoke developed: 0
Square-edged in standard panel sizes of 4 feet wide by 8, 9, 10 and 12 feet long, StructGuard installs as easily as standard gypsum sheathing, allowing "score-and-snap" cutting in the field. StructGuard is a cost-effective alternative to traditional wood-based sheathing with the added advantage of fire resistance.

High-Performance Exterior Sheathing

In the mid-'80s, BPB PLC, a diversified gypsum products manufacturer, developed and introduced its glass reinforced gypsum technology. More recently, the company introduced enhanced glass reinforced gypsum technology for use in its new high-performance exterior sheathing product GlasRoc.

EGRG is a patented technology that fully embeds reinforcing glass mats in a water-resistant gypsum core placed beneath a paperless, polymer-modified gypsum surface with a protective acrylic coating on the exterior face. With no starches, sugars, paper facing or pulp, testing per ASTM D 3273 demonstrated no mold or fungal growth after 28 days of exposure.

It is vapor permeable at 26 perms for 1/2-inch GlasRoc and 21 for 5/8-inch GlasRoc Type X, and has demonstrated strong flexural strength, pullout resistance and reduced humidified deflection (sag). It remained dimensionally stable when exposed to changes in temperature and relative humidity, the freeze/thaw cycle, UV light, wind, rain, snow and ice.

It is available in both 1/2- and 5/8-square-edged panels that are 4 foot wide by 8 foot long, with other lengths available.

The Type X version is included in UL designs for both wood- (U305, U309 and U301) and metal-framed (U465, U411 and U425) exterior wall assemblies. It is also inclusive in floor/ceiling assemblies G501 and L501, and beam and column systems N502 and X528, respectively. GlasRoc's acrylic/gypsum surface face resists delamination and the fully embedded glass mats provide a durable, dimensionally stable panel with uniform field and edge hardness.

It is ideal for use as a substrate for conventional stucco (cement plaster), shingles, shakes, metal siding, etc. Like gypsum wallboard, standard gypsum sheathing and glass-mat faced sheathing, GlasRoc is easily cut in the field by the score-and-snap method and uses the same fasteners and fastening pattern as standard gypsum sheathing.

Being lightweight, it is easy to handle and install, and its flexural strength allows it to bend to curves, making it ideal for vaulted exterior ceilings. The acrylic coating on the exterior face does not in any way inhibit the vapor permeability of GlasRoc sheathing. BPB offers a six-month limited warranty against exposure, a five-year limited warranty assuring product performance and a 10-year limited warranty as a substrate for EIF systems.

In part seven, we'll leave gypsum-based sheathing behind and take a look at the third category of sheathing products: cement-based.