There are several ways to locate studs in drywall. Traditional methods include visual inspection, gently tapping on the drywall with a hammer, and driving a small finishing nail into the wall. Modern technology has developed different and more efficient methods using density sensing and radar technology. Let's start with a look at the old-fashioned ways.
Sometimes, you can tell where the studs are behind drywall just by looking. When drywall is installed, the nails holding it to the studs are counter-sunk into the drywall, and putty, called drywall mud, is used to fill in the holes. By placing your face close to the wall and looking horizontally across the wall, you can often see small dents in the wall where the nails are. You might also be able to look across the wall from a doorway. Where there are nails, there are studs. The real problem with this method is that top-notch drywall installers won't leave this evidence behind.
Another method of locating studs is to use a small finishing nail to go on a fishing expedition. The drawback to this method is obvious--unwanted holes in the wall. There are better ways.
Before the advent of stud finders, the traditional way of locating studs was to tap gently on the wall with a hammer or other hard object. By listening carefully, you can hear the difference between the hollow sound of the space between studs and the solid sound when you tap on a stud. Using patience and very careful listening, you can find the center of a stud with a relatively high level of confidence. One drawback to this method is that on a well-insulated wall will not be able to hear enough difference in the sounds to have any confidence in your stud-finding ability. Other disadvantages of this method are that it requires very sharp hearing and great patience. Again, there are better ways.
The first mechanical stud finders were nothing more than free-swinging magnets in a glass of plastic case. When the magnet moves close to metal in the wall, it will swing toward the wall. While this works fairly well for detecting nails, it will also detect armored electrical cable and metal junction boxes. Any ferrous metal (iron or steel) or any magnetic field will cause the magnet to misbehave and give false results.
Electronic stud finders sense the dielectric constant of the wall. The dielectric constant will change as the density of the wall increases. By using a sensitive capacitor plate, the stud finder can not only locate studs, but also indicate the center of the stud. The stud finder is placed with its base, which contains a capacitor plate, in contact with the wall and moved along the wall until it indicates the presence of a stud. Newer models are self-calibrating for different thicknesses of sheetrock.
An even more modern stud finder uses radar to detect solid objects behind a wall. This device emits small impulses of radio waves and measures the time between the echoed waves returning to the device. Changes in the echo rate and strength tell the stud finder that a solid object has been located.
The methods of stud-finding range from very low-tech to very high-tech. The old manual methods are just not as useful as an inexpensive ($20 and up) electronic stud finder. This useful tool should certainly be in your toolbox.
