Learn industry best practices for finishing and decorating gypsum panels with the best possible results to save you money and time.
Controlling and maintaining environmental conditions is key to minimizing potential problems when finishing and decorating your gypsum panels. Temperature, humidity and airflow should remain constant and match occupancy conditions as closely as possible. Uncontrolled environmental conditions, (like changes or fluctuations in temperature, humidity and airflow) can have a profoundly adverse effect.
Changing job conditions and drying as the job atmosphere becomes more humid and saturated with water during joint treatment, painting or other wet operations and drying time (and time in between applications) can increase. At 55°F (13°C), with little ventilation, there can be as much as a four-time increase in drying time if room humidity elevates from 50% to 90%. Temporary liquid fuel heaters with open flames give off water vapor as a byproduct of combustion. As the ambient temperature rises (because warmer air holds more water), the relative humidity may go down, while the actual amount of water increases. (The combustion of 1 gallon of kerosene gives off over a gallon of water condensed). This will delay the dry-out time of plaster, concrete, joint treatment or other wet installations. Provide heat, if needed, to maintain temperatures above 55°F (13°C). Other atmospheric conditions at the jobsite can result in similar changes in drying times.
Using fill and finish coats of joint compound to properly conceal gypsum panel joints, fasteners and trim accessories makes it impossible to achieve a flat plane on a finished surface. However, a properly finished gypsum panel wall can minimize the appearance of joints, fasteners and trims. Its visual and aesthetic qualities help disguise the panel seams and points of fastener / trim installation from being easily visible across the substrate surface. Finishing and properly concealing joints and fasteners rely 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 doesn't properly conceal the panel. Instead, it increases the likelihood of joints and fasteners showing through the decorated finish.
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 dry, you may need to sand the joint compound.
Don't sand the compound flush to the panel surface; this will expose areas previously concealed. When sanding areas finished with joint compound, avoid roughening the panel face paper; roughened paper has raised fibers that are conspicuous after painting. If the paper is roughened accidentally, repair the damage by applying a small amount of joint compound with a 5-inch knife. 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.
Wet sanding with a damp sponge is a viable alternative to conventional dry sanding, especially when minimal sanding is required. Wet sanding is preferred whenever possible.
Wet-sanding methods aren't intended to remove large amounts of joint compound or compensate for poorly finished joints. Wet sanding produces no dust, which may eliminate the need to use a dust collector or respirator. It requires minimal cleanup and is less likely to scuff or damage the gypsum panel face or surface. Wet, sanded areas may be more easily concealed with paint finishes than dry sanded areas.
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, which still allow an acceptable sanding rate, are preferred.
There are three major types of sanding materials: sand paper, 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 or finer, 80μm (micron) sanding film or finer.
If dry sanding, wear a NIOSH / MSHA (National Institute for Occupational Safety and Health and the Mine Safety and Health Administration)-approved respirator. Dust created from dry sanding may cause eye, nose, throat or upper respiratory irritation. If there's any discomfort, consult a physician.
For paper-faced gypsum board, treat the surface with a primer-surfacer, or apply a skim coat and primer.
When applying a skim coat, cover the entire surface with joint compound, then immediately shear-off excess compound using a drywall broad knife to force the compound into surface pores and imperfections.
The skim coat should be installed with a trowel-applied consistency and allowed to dry thoroughly before lightly buffing and sanding trowel lines and minor imperfections. Once the surface is smooth and free of tool marks and ridges, lightly brush to remove sanding dust. Apply a coat of primer over the entire surface prior to the application of decorative finishes. A skim coat won't approximate a plastered surface.