USG Finishing and decorating glass-Mat gypsu M panels - Manual (Page 2)

To minimize sanding, apply joint compound over joints, fasteners and accessories as smoothly or
without defects as possible. Once the joint treatment phase is complete and the joint compound is
thoroughly some sanding of the joint compound may be required. To minimize texture variations
avoid sanding the panel face. note: DO NOT sand compound flush to panel surface; this will
expose areas previously concealed. Avoid using excessively coarse or larger-sized abrasive media
(or grit) that may leave visible scratches in the joint compound after painting. Remove all sanding
dust prior to applying any surface treatments (primer or primer-surfacer).
Wet sanding: Wet sanding with a damp sponge is preferred whenever possible, especially when
minimal sanding is required (refer to USG Technical Literature J-610 for more information).
note: Wet sanding methods are not intended to remove large amounts of joint compound or
compensate for poorly finished joints. Wet sanding produces no dust and requires minimal clean-
up; it is less likely to scuff or damage the panel face surface. Wet sanded areas may be more easily
concealed with paint finishes than dry sanded areas.
dry sanding: Either manual or power equipment can be used for dry sanding, which uses abrasive-
faced material to remove joint compound from gypsum panel joints, fasteners and trims. Sanding
materials with abrasive media or grit, sized as fine as possible are preferred. There are three major
types of sanding materials: sandpaper, mesh and film; all offer a variety of grades. Good results
can be achieved by using: 150-grit sandpaper or finer; 220-grit abrasive-mesh.
Glass-mat panels differ from paper-paced gypsum panels in the treatment of the panel surface in
the following conditions:
level 3 Finish: recommended in areas where one or more of the following conditions exist:
1. Areas to receive heavy- or medium-texture (spray or hand applied) finishes before painting
2. Heavy-grade wallcoverings are to be applied as a final decoration
3. Wallcoverings to be applied
note: This level of finish is not recommended where smooth painted surfaces or light to medium
wallcoverings are specified.
When glass-mat panels transition to a dissimilar substrate material(s) and a textured wall pattern
is specified that leaves a portion of said wall surfaced exposed (without texture) prior to painting:
apply a skim coat 2 of all purpose joint compound at a trowel-applied consistency to entire surface
and let dry. The skim coated surface must be smooth and free of tool marks and ridges (a light
sanding of the skim coating may be necessary to remove tool marks). Remove sanding dust
from surface, then apply one full coverage coat (5-10 mils WFT [Wet Film Thickness]) of USG
Sheetrock® Brand First Coat primer or equivalent to cover surface. Allow surface to dry prior to
decorating. Refer to USG Technical Literature: J1095 for more information regarding First Coat
primer; J510 for more information on skim coating.
level 4 Finish: recommended in areas where one or more of the following conditions exist:
1. Flat paints and smooth wall applications
2. Light textures to be applied
3. Wallcoverings to be applied
note: In critical lighting areas, flat paints applied over light textures tend to reduce joint
photographing. Paints with sheen levels other than flat and enamel paints are not recommended
over this level of finish.
Apply a skim coat 2 of all purpose joint compound at a trowel-applied consistency to entire surface
and let dry. The skim coated surface must be smooth and free of tool marks and ridges (a light
sanding of the skim coating may be necessary to remove tool marks). Remove sanding dust from
surface, then apply one full coverage coat (5-10 mils WFT) of USG Sheetrock® Brand First Coat
primer or equivalent to cover surface. Allow surface to dry prior to decorating. Refer to USG
Technical Literature: J1095 for more information regarding Sheetrock® Brand First Coat primer;
J510 for more information on skim coating.
level 5 Finish: recommended in areas where one or more of the following conditions exist:
1. Exposure to critical/severe lighting
2. Paints with sheen levels other than flat are specified
3. High value spaces exist where the highest quality finish is expected
Apply a skim coat 2 of all purpose joint compound at a trowel-applied consistency to entire surface
and let dry. The jobsite standard(s) shall dictate if additional skim coat(s) are required. The skim
coated surface must be smooth and free of tool marks and ridges (a light sanding of the skim
coating may be necessary to remove tool marks). Remove sanding dust from surface, then apply
sanding
surFace treatMent