When tackling carpentry projects in our older homes, we can choose from a vast array of fasteners to hold wooden elements together. Most of these fasteners can be readily found at the nearest home center, where shelves full of nails and screws seem to come in endless varieties.
How can we make sense of all these selections and determine which is the best fit for a specific task? It helps to start with some historical background on traditional fasteners. Knowing how they evolved, how they were used traditionally, and even how they hold things together is critical to understanding that not all fasteners are created equal.
Two hundred and fifty years ago, when homeowners and builders needed to join two or more pieces of wood together, they had several types of fasteners at their disposal, and each was used for a different purpose. Large timbers were almost always joined with treenails or trunnels, which we know today as pegs. Smaller planks and boards were commonly joined with handmade nails. These wrought nails were used on everything from flooring to cabinet hinges. Blacksmiths would carefully fashion a variety of nails and customize their heads, depending on their intended use—nails with tiny, flat heads, for example, were used to fix trim in place, while nails with hook- or L-shaped heads were used to fasten flooring. During this time, handmade screws, which were individually filed and pointed, were also produced in limited quantities. These were generally used only on cabinetry and furniture.
By the late 18th century, mass-produced nails—cut by machine from sheets of iron—were introduced. As a result of their low cost and ready availability, they quickly supplanted hand-wrought versions. Several years later, machine-made screws also appeared, which greatly increased their use as anchors for all types of hardware. It wasn't until the late 1840s, though, that machine-made screws with pointed heads arrived, thanks to new technology that made it possible to turn a pointed thread. (The earliest machine-produced screws had flat bottoms.) Craftsmen quickly realized that these worked better than flat-bottomed screws, so the new screws found widespread and rapid acceptance. By the middle of the 19th century, the Industrial Revolution enabled another fastener innovation—manufactured nails cut from long reels of extruded iron (and later steel) wire, which could be produced more quickly and cheaply.
The homebuilding industry became increasingly dependent on these to fasten together new balloon and platform framing systems, but elsewhere, wire nails did not immediately replace cut nails. Craftsmen from roofers to trim carpenters abandoned cut nails reluctantly, so the process took more than half a century. It is not uncommon to find houses built with cut nails during the first half of the 20th century, because many carpenters were convinced of their superior holding power. A look at the way nails hold wood helps explain the preference (see "Staying Power," below).
Screws do two things very well: They hold securely, allowing you to adjust how tightly materials are connected, and they can be repeatedly installed and removed. Screws also are invaluable when either the material you're fastening or the substrate you're connecting it to will be damaged by the pounding of a hammer on a nail. (A plaster wall, for example, is much less damaged by the driving of a screw than the pounding of a nail).
Trimhead screws, which were introduced in the past 20 years, leave only a small head showing, so they can sometimes be used in place of finishing nails. They make an excellent way to secure stop moldings, but there can be a dark side to using a screw where it isn't expected or where the head is intentionally countersunk and filled for painting.
Someday a future homeowner will be prying apart that molding and encounter your hidden line of screws, which will either splinter the wood as it is separated, or require hours of time spent hunting for and removing the hidden fasteners. As old-house owners, we have a responsibility to those who follow us, and all of our repairs should be readily apparent—even through paint—and easily reversible. I sink trimhead screws so their head is just flush with the wood's surface. Once painted, the tiny square recesses left behind will clue future craftsman in to the fact that screws join the materials. To enhance the visual appeal of a traditional house, try using slotted screws, which were the type most readily available until the mid-1920s.
Nails are relatively inexpensive, can be installed quickly, and hold securely. For this reason, they have been the fastener of choice in homebuilding since about 1830. To this day, they remain the fastener relied on most by homebuilders. Where nails are used, reversibility is implied. Almost all nails can be removed simply by prying. There are, however, some varieties designed to resist pull-out, such as cement-coated nails, in which the heat generated from the friction of driving the nail momentarily liquefies an adhesive that keeps the nail in place. Other nails have shanks that are ridged or cut with a screw-like spiral. Both types damage wood as they are removed, and should be avoided whenever possible.
To retain the visual appeal of your 18th- or 19th-century house, consider using reproduction nails. These are usually cut nails that can be finished with either a "rosehead" (a blacksmith-styled shallow pyramidal head once used on nails that attached hardware or flooring) or a flat head characteristic of original cut nails.
Nails or Screws?
As a general rule of thumb, you should always replace nails and screws with similar fasteners, particularly if you are completing a faithful restoration. While this seems like simple advice, it's sometimes tempting to swap one out for the other. For example, whenever I encounter interior stop moldings on windows that are secured with nails, I consider replacing the nails with screws, because windows need regular maintenance that usually requires removing one or both sashes. Screws make this job easier.
All fasteners are usually available in bright (uncoated), galvanized, or stainless steel. For outdoor use, choose the most corrosion-resistant material you can find. Stainless steel nails are significantly more resistant, but can be considerably more expensive. In addition, while almost all hardware departments will carry galvanized nails, many sizes and styles of stainless steel nails have to be mail-ordered. Also, be sure to match the metal to the wood. Certain species of wood (redwoods and cedar) react with galvanized nails to produce staining and corrosion. In this case, stainless steel is the best choice. And although copper nails are considered appropriate for roofing, copper corrodes quickly in the presence of the tannins contained in split oak shingles. Here, galvanized or, better still, stainless steel is preferred.
Many homeowners (and even some professionals) are unclear about how nails hold wood together. It's actually the wood—not the nail or the head—that does the holding. Driving a nail into a piece of wood forces the wood fibers to tear. The direction the nail travels orients the fibers downward, pressed tightly against the nail's shank. The greater the surface area of the nail, the greater the number of locking fibers, hence the superior holding power of cut or wrought nails.