Wrought iron nails. The way a building is put together often gives you clues about its age. From ancient Egypt until a couple hundred years ago, nails were made by hand by blacksmiths; these wrought iron nails were expensive, so it was to a builder's advantage to avoid using them. Timber-framed buildings like the one pictured (a modern timber frame), can be built without any nails. The pieces fit together and stay in place with wedges or wood dowels. I keep an old tapered wood peg I pulled out of a job in my tool bag to remind me how much time and care went into building in the past. In the age of nail guns, it's too common to shoot first and ask questions later.
Wire nails. Most nails today are wire nails — basically a length of wire with a point at one end and a head at the other. There's some history in wire nails' designations. If you see a nail with the designation 8d, that's an eight-penny nail, the price you would have paid for 100 nails in the 15th century. You won't be so lucky today! Though once you've driven 100 eight-penny nails by hand, the price will be the last thing you're complaining about.
Rather than try to describe all of the other types of nails available, I'd like to help you learn to read nails. If you can read a nail, you can determine the right use for it. Here are three different nails and how their different characteristics suit their uses.
Roofing nail. The large head is the first thing to notice about the roofing nail. A shingle is not as thick or dense as wood, so a small head might tear a shingle. Roofing nails aren't generally very long, because you are attaching something thin (roofing) to plywood, which is also relatively thin. You want two-thirds of the nail to be driven into the thicker of the two materials you are fastening, so ¾-inch plywood and shingles mean a ¾- to 1-inch nail should do the trick.
When nailing wood to wood, it's rare that a nail that small would be helpful. In fact, when a nail other than a roofing nail is smaller than 1 inch, it's called a brad instead of a nail. The other thing to notice is the dull gray finish. This is a galvanized coating that protects the nail when it is exposed to the elements. This is important for exterior applications like roofing.
A common nail is longer than a roofing nail, since you'll usually be fastening 1½-inch wood to more wood. The common nails shown here are 3 inches long.
Hammer. Using a hammer is the classic way to set a nail. My hammer, pictured here, is a framing hammer designed to put less strain on your wrist. Claw hammers allow you to pull and set nails, and they come in different sizes. Get a hammer that feels good to you and watch where you swing it. A little concentration will save your thumb.
Powder-actuated tool. Powder-actuated tools have a small gunpowder cartridge that's activated by pulling a trigger or hitting a button with a hammer. The gunpowder shoots a nail out of the device. These tools are most commonly used for fastening wood or metal studs to concrete. Use caution; as with a gun, kickback is a concern, so brace your body and keep your face away from the tool. If you're using the type you hit with a hammer, the hammer can also kick back. I learned this the hard way with a claw to the forehead.
Nail gun. A nail gun is actually less gun-like than a powder-actuated tool, in that it uses air to fire the nails instead of gunpowder — but it is still very dangerous. You should use your foot (in a steel-toe boot), not your hand, to brace the wood while you fire. Nail guns are available to shoot roofing nails, finish nails, brads etc. Each nail requires a different gun, though, so if you will be setting a limited amount or are not experienced, stick to setting nails with a hammer.
Construction adhesive is good for framing, and good old wood glue works well for trim work and furniture.
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