Drywall Installation vs wood screws

Drywall and Wood screws are designed for different purposes

The differences in these screws are the threads, thread length, metal types, coatings, and drive.

• Drywall Screws are a #6 shank screws with a #8 screw head
• Drywall Screws have a Bugle Head to dimple the paper on the drywall, not break it as a Flat Head screw would do.
• Drywall Screws are hardened. That is why they will snap more easily than a wood screw.
• Drywall Screws are threaded to the underside of the head. Under any conditions, it will not pull two pieces of wood together to make a tight joint. The head will snap off before you pull the joint tight.
• Drywall Screws are coated to prevent rusting from the moisture in the drywall mud used to cover them up.
• Drywall Screws use a Phillips Drive for slipping when the correct depth is reached using a special tool.

Drywall screw threads, when used with wood studs, are coarse. This full-threaded design is for a material that does not absorb water. The Phillips drive is designed to cam out under pressure. Overdriving screws into drywall can cause problems. The screw will be attached to the wood stud, but the ripped-out treads in the gypsum board will not have much holding power. The black phosphorus coating is a light coating that ranks low, below zinc in terms of rust prevention. The most common and affordable drywall screws sold are a #6. This size screw is for small crafts, hinges, drawer slides, children's furniture, toys, light-duty jigs and fixtures, etc., light-duty.

The most common and affordable wood screws sold are the larger #8. This screw is for general furniture construction, cabinets, and light construction. Drywall screws are more brittle and will snap off, and like the Phillips cam out, it is by design. Over-driving drywall screws causes more problems. The idea is you would rather drive another screw, tape, and mud two small holes than have one larger problem. Drywall screws are fully threaded. This full threading can help hold drywall, but it pushes the wood apart rather than pulling it together as you tighten it.

Why Wood screws are different.

A wood screw is designed to work like a clamp. The head of the screw and the threads are designed to pull the project together. Woods screws are not fully threaded. Most have about 1/3 of the shank unthreaded. If there are threads in the middle where the wood meets, it can pull the joint apart. Wood will absorb water over time, expanding and contracting. In the example of a deck board that gets wet often, this problem is called "board jacking." The boards are under pressure at the joint. As the board swells or contracts, the treads inside the wood will stay in place, but the wood will rip apart at the joint, where the spacing will change. The drywall does not expand. Our Shop screws have a saw tooth thread design, and dry-lube coatings make driving them easy. Wood screws get heat-treated, making them stronger. Wood screws are available in many coatings, head designs, and threads. They can fit many different applications and have IBC ratings for code compliance.

The McFeely’s 2/3 Rule for Screw Length

There is no hard and fast rule concerning wood screw length requirements. Sometimes, you have little choice regarding length because of the construction details. In general, though, the screw should always go through the thinner piece and thread into the thicker piece. In choosing length, try to have about 2/3 of the screw threaded into the "secondary" piece, as shown. However, as the thickness of the lumber increases, this ratio can be reduced so that only 1/2 of the shank is threaded into the secondary piece. Not coincidentally, only 2/3 of the shank is threaded on our 1 in. and longer screws.

Application Info: Fastening Drywall

Yes, there is a legitimate use for "drywall" screws! Drywall (also known as Gypsum Board, plasterboard, or Sheetrock) is compressed Gypsum powder sandwiched between two layers of heavy paper, so you can imagine that fastening it to the wall structure requires specialized fasteners. 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 oversized heads (about the size of a #8 wood screw). The oversized 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 in. (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 in. (the most common for ordinary construction), and 5/8 in. (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 (22-ga) or heavy-gauge (20-ga) steel studs are used primarily for commercial construction and require a screw that can pierce the steel stud and cut its 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 screw gun with an adjustable nosepiece. When the screw reaches the desired depth, the Dimpler or screw gun 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 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 six in. along the outside vertical edges and fasteners every 12 in. in the field (middle) of the sheet. Remember to check your local code for any special requirements.