USG Finishing and decorating glass-Mat gypsu M panels - Manual

Finishing and
decorating
glass-Mat gypsuM
panels
USG Sheetrock® Brand Glass-Mat Panels Mold Tough® are high-performance interior wall panels
suitable for use in pre dry-in applications of wallboard (aka pre-rock) and similar applications before
the building envelope is fully enclosed. They can be exposed to the elements for up to 12 months
and are moisture and mold resistant. The fiberglass facing and back shed water and the panels score
10 out of 10 on the ASTM D3273 test for mold. 1 Though glass-mat panels can be substituted for and
installed similar to regular drywall, the fiberglass facing of the panels is distinctly different than
paper facing and needs to be finished differently than paper-faced gypsum panels when receiving
decoration. The texture of the panel and absorption of paint is dissimilar to paper-faced gypsum
panels and requires an additional skim coat of joint compound in most applications.
There are currently no consensus industry recommendations or standards for finishing glass-
mat gypsum panels. USG is working with several industry associations to update the GA-214
Recommended Levels of Gypsum Board Finish publication to include new finishing recommendations
for glass-mat gypsum panels. The following guidelines can help improve success at the jobsite.
In addition to written project documents, a full scale project standard(s) of the approved wall and/
or ceiling configuration(s) should be erected on the jobsite by the contracted workforce so as to
provide a visual benchmark. It should be finished and decorated in accordance with applicable
project specifications set by the design and specifying/approving entities. Jobsite constructed
standards should be evaluated for appearance, and agreed to by all stakeholders prior to
conducting any widespread finishing work and/or production painting.
Determining the appropriate level of finish is dependent on a number of factors. Primary
architectural considerations include the location within the structure, critical lighting conditions
present, wall smoothness desired, and the color, type, and sheen/gloss of the decorative finish
specified. Once all of the factors have been evaluated, project documents can be written in specific
terms and jobsite visual standards created, enabling contractors to be better prepared to present
their most competitive bid.
Install panels as outlined in ASTM C840 Standard Specification for Application and Finishing
of Gypsum Board and GA-216 Application and Finishing of Gypsum Panel Products. For fire rated
applications, conform to assemblies published in GA-600 Fire Resistance Design Manual and UL Fire
Resistance Directories. After installation, make sure that all panel surfaces are completely dry and
free of dirt, grease and dust. Panels should not be finished until building is completely enclosed.
Joints between USG Sheetrock® Glass-Mat Panels Mold Tough® may be finished with either USG
Sheetrock® Brand Paper Joint Tape embedded in USG Sheetrock® Brand All Purpose Ready-Mix Joint
Compound or Sheetrock® Brand Fiberglass Drywall Tape embedded in USG Sheetrock® Brand
Setting-Type Joint Compound. Tape all joints and interior angles. After embedding tape, immediately
wipe joints and interior angles with a joint knife, leaving a thin coating of joint compound.
For proper concealment, use USG Sheetrock® Brand All Purpose Joint Compound. For smooth wall
applications, apply two separate coats over all flat joints; one separate coat over interior angles;
and three separate coats to cover fasteners and accessories.
Using fill and finish coats of joint compound to properly conceal panel joints, fasteners and trim
accessories makes it impossible to achieve a flat plane on a finished surface. However, a properly
finished panel wall can minimize the appearance of joints, fasteners and trims. Finishing and
properly concealing joints and fasteners relies on two techniques: (1) using graduated arcs to
prevent recesses or ridges and (2) not applying joint compound flush or flat to the panel surface.
Recesses or ridges can result in distinct shadows in critical light or other adverse visual conditions.
Applying joint compound flush or flat to the surface does not properly conceal the panel and
increases the likelihood of joints and fasteners showing through the decorated finish. For more
information, refer to USG Technical Literature J2010 Finishing and decorating gypsum panels.
Job standard speciFication
(Mock-up)
panel installation
Joint taping
proper concealMent