Locating a stud behind drywall is easy. All conventional stud finders, from the best down to the worst, do a more-or-less good job of finding studs behind drywall.
For one, the more layers you add into the equation, the less reliable the stud finder's results will be.
For another, ceramic or porcelain tile often has different substrate materials than an ordinary drywall stud wall: cement board (such as Durock or HardieBacker), different fasteners, layers of thinset (mortar), and even metal studs, in some cases.
But there are ways to do it, beginning with the most reliable, fail-proof way (radar scanners) to the least reliable (magnetic finders).
1. Ultra Wide Band (UWB) Scanner
For finding a stud behind drywall, a UWB scanner is expensive overkill. For problem materials like dry or wet concrete, floor heating, 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 use radar technology.
If you can borrow, buy, or rent a UWB scanner, it is the surest way to find a stud behind drywall.
2. Dielectric Constant Stud Finder
Complicated name aside, a dielectric constant (DC) stud finder is the 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 stud--behind the covering surface.
DC stud finders do a poor-to-middling job of locating studs behind tile. They return a host of false-positives. However, if you combine a DC stud finder with intuition and detective work (below), you can do a fairly good job of locating studs.
3. Intuition and Detective Work
- Sixteen Inches On-Center: Studs tend to be spaced every sixteen inches on center. So, start from the corner of the shower, measure off sixteen inches, mark that area. You have a reasonably accurate idea of where a stud is located now.
- 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 joint compound. With tile, you cannot drill through the tile itself. Instead, drill pilot holes through the tile grout. Use small bits to start with. Use something thin, like a finish nail, to insert in the hole to feel whether there is a stud back there. Cover holes up with grout.
4. Rare Earth Magnetic Stud Finders
These stud finders are hopeless against 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.
Finally, if the rare earth magnet will not work, you should not expect the old-school rod-style magnetic studfinder to help.
Suggestion: Attach Item to Tile, Not Stud
Consider if there is any way to avoid going all the way to the stud.
One reason you might go to the stud is if you are mounting a grab bar or other assistive device. If you are installing a soap dish or other light-weight item, these are installed on the tile surface with epoxy.