Drywall Sanding Corners
This article is an snippet from the book called “Drywall Taping” – Workbook. This article gives a detailed description about drywall sanding corners.
Sanding, like any other operation in the taping trade, can be made difficult or it can be a relatively easy part of the work. When a worker uses the proper tools, the correct type paper, and has an understanding of what he is trying to accomplish, the necessity for sanding is minimized and such sanding as is required is simplified.
It is not necessary to apply heavy pressure when hand sanding or using a sanding pole. The sanding block and sandpaper should do the work. With the correct sandpaper (the most commonly used is 80 0r 100 grit),a taper can do the necessary sanding without it becoming a difficult or tedious chore.
A prime factor in making sanding easier is in having used reasonably soft finishing compounds when taping the job. The proper selection of finishing compounds can save time and work with the sanding operation. If bedding cement is used for final coats rather than finishing compound, the sanding process is made twice as difficult. This is because bedding compound, when set up, presents a relatively hard surface and is not so readily sandable.
Preparation and Sanding
When the joints are run correctly with the finishing tools and checked prior to sanding by hand, the result will be a smooth finish that needs very little sanding. The edges of the finished joints and fastener covering should be sanded lightly to eliminate any rough edges. Some shops use a sponge and water to smooth edges. This like sanding, is a skill acquired by practice and “feel.” If the joint is wiped too hard and too much water is used, the feathered edge will not remain smooth. The same is true when using sandpaper. Excessive sanding will not only change the feathered edge but will also raise the nap of the face paper, causing difficulty for the painter. If excessive sanding is required, the application of the joint cement and/or finishing compound was incorrectly accomplished.
“Touch-up” and Second Coat Sanding
The touching-up process is a very vital part of sanding to obtain an ultimately smooth surface. Any scratch lines, recesses, or imperfections should be marked or remembered when sanding. After being sanded, some areas will always need an additional hand application of joint compound.
A light sanding between the second and third coats is very helpful and necessary. It shortens the time consumed I n the final sanding by creating a smooth surface for the finish coat or coats.
This topic, “Third Coat-Skimming,” is planned to provide answers to the following questions:
- What is purpose of the third coat or “skimming”?
- How thick should the joint compound be applied with the Ames flat finisher?
- What consistency should the joint compound be when using the flat finisher and the corner finisher?
- Why is it important to have a reasonably clean working surface?
The third coat of compound over the taped joints and butt joints is applied after the second coat is dry. A light sanding of any burns or splattered joint compound or other material that may have gotten on the surface of the wallboard is necessary to eliminate scratches or chatters in the finished third coat.
The constiency of joint compound for the third coat is similar to the thickness of the material used for the second coat. It is thick enough to be workable with tools and thin enough to apply only the necessary thin finishing coat to the joint.
This coat will extend as need beyond the edge of the second coat, which may vary from 7 to 10 inches wide on recessed seams or joints and 15 to 20 inches on butt joints. All excess compound remaining at laps, at a crossing, or at an intersecting joint should be wind smooth so that little or no extra work will be required.
After all the joints have been coated, it may be necessary to recoat a remaining joint that is hollow or sunk. An extra few minutes will make the job more complete and save time in the next step preparation of the finishing job.
Corner Finishing by Machine
Corner finishing is accomplished quickly and easily with the Ames corner finisher by using a thinner joint cement than is used in the second or third coating. After ensuring that the inside corners are dry and sanded to remove any ridges or splattering of joint compound or other material, the corner finisher is placed at the top of a vertical corner and the finisher blades depressed so as to produce a smooth feathered edge finish. The tool is then guided downward, maintaining pressure at the center of the corner. When the tool is as close to the bottom of the corner as the operator can reasonably maneuver it, for instance one foot from the end,
The pressure is released and the tool is turned in the hand to permit an upward stroke similar to the downward stroke. The corner finisher is then placed in the horizontal angle of the intersecting ceiling and wall angles. A similar pressing in of the corner finisher, along with walking forward-with the pressure of the tool being directed to the center of the corner or angle-results in filling the shrinkage and at the same time feathering the edges. When a certain number of angles are run in this manner, depending on drying conditions, wiping-in will begin. This consists of pointing-up or wiping-in each area and making a neat square corner. This may be done with a 6-inch broad knife or a 7-inch wipe-down knife.
Care must be taken to keep the corner finisher tool clean and undamaged so that it will produce good, clean trouble-free work. Dropping the corner finisher may break the finishing blades, which will then have to be repaired.