Finding a stud behind ceramic or porcelain tile is more complex than behind gypsum because, for one, tile walls can be thicker than drywall. The more layers you add, the less reliable the stud finder's results will be.
Not only that but the thickness of ceramic tile wall installation may not be consistent. When the thinset mortar is laid down, it's supposed to be even. But inevitably, high and low areas may develop.
Ceramic or porcelain tile often has different substrate materials than an ordinary drywall stud wall: cement board (such as Durock or HardieBacker); tile uncoupling mats; various fasteners; layers of thinset (mortar); and possibly even metal studs. If the tile itself happens to be metal, then magnetic stud finders cannot locate the stud.
- Stud Finder: Begin with the least expensive method: running a conventional dielectric constant (DC) stud finder across the surface. This is the most common type of stud finder. In some cases, the stud finder may be able to sense the dense mass of the stud behind the tile.
- Magnetism: Rare earth stud finders are super-sensitive, powerful magnets that you run across a surface in hopes of detecting a metal fastener underneath. Tile isn't secured by metal fasteners, but its cement board substrate often is.
- Intuition and Detective Work: Knowing that studs are usually placed 16 inches apart from each other is your most important clue in locating adjacent studs.
- Ultra Wide Band (UWB) Scanner: The ultimate tool in finding just about any material under any other kind of material is a professional-grade tool called an Ultra Wide Band (UWB) scanner.
Tools For Detecting Studs Under Tile
Locating a stud behind drywall is easier with the right tools. Most conventional stud finders do a relatively good job of finding studs behind the drywall. Drywall is soft and crumbly, and its thickness is constant. But when confronted with ceramic, porcelain, or stone tile, stud finders aren't always as reliable.
Dielectric Constant Stud Finder
Complicated name aside, a dielectric constant (DC) stud finder is a kind that you may already have on hand. This is the type of stud finder that you slide across a wall until a red light signals that there is a solid mass such as a wooden stud behind the covering surface.
Dielectric constant stud finders do a poor job of locating studs behind tile as they are prone to returning a host of false-positives when there is a lot of dense materials in the area.
- Run a strip of painter's tape across the surface, horizontally.
- Above or below the tape, pass the DC stud finder across the tile surface from side to side. Go very slowly.
- Whenever there is a positive, no matter how weak, mark it on the tape with a pencil.
- After making multiple marks, you may begin to see a pattern develop. Clusters of pencil marks will indicate the presence of a dense item below such as a stud.
Rare Earth Magnets
Magnetic stud finders are highly effective at finding studs behind drywall but far less effective at finding anything under the many layers of tile and tile substrate.
You may be able to detect a fastener, but only if you go slowly and are patient and if the substrate is unusually thin. This is a possibility since tile thinset often fails to extrude through the tiler's float at a uniform thickness.
Wall studs tend to be spaced every 16 inches on-center. Start from the corner, measure off sixteen inches, and mark that endpoint. With this, you have a rough idea of where a stud is located now.
On-center is a building term that means that you should measure from the center of one stud to the center of the next stud.
One method of fine-tuning your sixteen inches measurement is by drilling tiny investigative pilot holes.
With drywall, it is not uncommon to drill a number of small holes or use a thin finish nail to explore various areas before you hit a stud. Drywall covers up easily enough with a quick smear of Spackle or joint compound, followed by a touch of paint.
But with tile, you cannot drill through the tile itself. The solution is to drill pilot holes through the tile grout, not the tile face. Use small bits to start with. After you have drilled the hole, use something thin, like a finish nail, to insert in the hole to feel whether there is a stud back there. You may have to drill several holes to locate the stud. After you have located the stud, mark its position with a tag of painter's tape on the tile. Cover up the holes up with grout.
The chief reason you might attach an item directly to the stud is if you are mounting a grab bar or other assistive device. But if you are installing a soap dish or other light-weight item, there is no need to drill holes or find studs. These items are installed on the tile surface with epoxy.
Ultra Wide Band (UWB) Scanner
For finding a stud behind drywall, a UWB scanner is pricey and excessive. But for thick, dense, or otherwise problematic materials like dry or wet concrete, floor heating ducts, or metal, UWB scanners are indispensable.
UWB scanners are unlike any other stud finder that you have used. Instead of searching for metallic fasteners, UWB scanners use radar technology. In fact, UWB scanners are such a big deal that, at various times since their introduction, the Federal Communications Commission (FCC) has required that operators register their devices with the FCC.
If you can borrow, buy, or rent a UWB scanner, it is the most accurate method of finding a stud behind a tile wall. If any tool can be considered a stud finder for ceramic tile, it would be a UWB. Unfortunately, for most do-it-yourselfers, a UWB scanner is likely too costly and too complicated a tool for a minor project such as this.