| Application info: Fastening drywall. |
Yes, there really is a legitimate use for “drywall” screws! Drywall (also known as Gyp Board, plasterboard, or sheetrock) is basically compressed Gypsum powder sandwiched between two layers of heavy paper, so you can imagine that fastening it to the wall structure requires specialized fasteners. In fact, there are a variety of screws commonly used to “hang” drywall, and each one is designed for a specific situation. The one common feature of all drywall screws is the very smooth “bugle head” curved transition between the shank and head. In addition, drywall screws generally have thin shanks (about the size of a #6 wood screw) and oversize heads (about the size of a #8 wood screw). The oversize head and smooth transition zone are designed to minimize tearing through the drywall's heavy paper face — something which largely eliminates the screws’ holding power.
There are four common sizes of drywall: 1/4" (used for skinning existing walls, or sheathing curved surfaces in multiple layers), 3/8" (generally used in a two-layer wall system for extra strength), 1/2" (the most common for ordinary construction), and 5/8" (used when extra strength or a fire rating is required). In addition, specialized types of drywall called blue board or green board are designed for wet environments like bathrooms — but they are still fastened with drywall screws.
Screw Types: Coarse threaded screws are best when fastening to the softwood studs typically used for residential construction. Light gauge (22ga) or heavy gauge (20ga) steel studs are used primarily for commercial construction, and require a screw that can pierce the steel stud and cut its own threads. For light gauge framing, a simple sharp pointed fine thread screw is sufficient. Heavy gauge steel studs require a fine threaded drill point screw.
Drive Type: The Phillips recess of most drywall screws gives them an advantage over the square recess used in top-quality wood screws. Most drywall screws are driven using a “dimpler” or specialized screwgun with an adjustable nosepiece. When the screw reaches the desired depth, the dimpler or screwgun nosepiece contacts the drywall surface, reducing the bit connection with the screw, which causes it to cam out. The more positive engagement of the Square Drive recess does not allow it to cam out as easily, making it difficult to avoid paper tears. It may be crude, but the system is very effective, and it keeps driver bit manufacturers in business.
Fastening Schedule: Many installers simply screw or nail the drywall to the stud. Professionals use screws and nails to clamp the drywall to the stud while the panel adhesive cures! Glued panels provide more strength and a quieter structure than panels attached with screws or nails alone. Installation starts with the application of a generous bead of panel adhesive to the studs. After placing the drywall, several nails are quickly driven to hold the sheet in position. Screws are then used to pull the panel tight to the studs while the adhesive cures. Most codes require fasteners every 6" along the outside vertical edges, and fasteners every 12" in the field (middle) of the sheet. Remember to check your local code for any special requirements.
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