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Choose the right bit for the tile
Concrete roof tiles are hard, brittle and often glazed. A bit that cuts quickly into a block wall can skate across a tile’s surface or crack it if you start with hammer action. For most holes through a roof tile, buy a sharp carbide-tipped masonry bit sized for the fastener, and drill the tile in rotary-only mode. Switch to hammer mode only after the bit has passed through the tile and reached the supporting masonry, if the drill and bit are suitable for that material.
Check the fastener instructions before choosing a diameter. A screw-and-plug system may call for a hole slightly larger than the screw, while a screw designed for direct masonry anchoring may specify a different size. Don’t guess from the screw’s outside diameter: the anchor manufacturer’s stated drill size is the useful number.
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Masonry bit options compared
| Bit type | Best use | Trade-off |
|---|---|---|
| Standard carbide-tipped masonry bit | Occasional holes in ordinary concrete or clay tiles | Affordable, but the tip may blunt sooner and can be awkward on glazed surfaces |
| Multi-material bit | Small, careful holes in glazed or brittle tile | Can start cleanly in rotary mode, but may be slower in concrete; follow its stated material limits |
| Four-cutter carbide masonry bit | Repeated holes or tougher masonry behind the tile | Usually more durable and less prone to catching, but costs more |
| Diamond tile bit | Hard, glazed surfaces where carbide keeps skating or chips the finish | Often slower and may require cooling; not a substitute for a masonry bit once into the substrate |
For a one-off repair, a decent standard carbide bit is usually enough. A carbide-tipped masonry bit set is a sensible buy if you need several diameters, but check that the set includes the size your anchor actually requires. For regular work, a four-cutter masonry bit is worth considering for its tougher head and steadier cutting in masonry. It still needs careful handling on the tile itself.
Use the drill’s modes carefully
A cordless drill with a rotary setting is enough to make a hole through many roof tiles. A hammer drill is useful for the masonry underneath, but its percussion can fracture the tile, especially near an edge, an old crack or a fixing hole. Turn hammer action off while drilling the tile. If the supporting material is concrete or dense brick, change to hammer mode only once the bit has cleared the tile and the anchor instructions permit it.
Use a standard drill chuck for round-shank bits. SDS bits need a compatible SDS chuck and are generally more useful for hammer drilling the substrate than for carefully starting a tile hole. An impact driver is a poor choice: its impacts are rotational, not the controlled axial hammering a masonry bit is designed for, and the sudden torque can damage the tile or bit.
Small cordless drills can do the job, but a tired battery or low-speed, high-pressure approach can overheat the bit. Use a fully charged battery, a moderate speed and light, steady pressure. If the bit stops cutting, withdraw it, clear dust and let the bit cool rather than leaning harder on the drill.
A safer drilling sequence
First make sure the tile is supported. Don’t drill a loose tile or put body weight on one; roof tiles can crack under concentrated pressure. Roof work also carries a serious fall risk. Work from a properly secured position, use suitable fall protection where required, and avoid stepping on tiles unless you have a safe method and know where they are supported. If access is unsafe, use a qualified roofer.
Mark the hole and place masking tape over the spot if it helps the bit stay put. Use a sharp bit, hold the drill square to the tile, and start slowly in rotary-only mode. Keep pressure light until the tip has made a clear, shallow seat. Then drill at a steady pace. For a larger opening, pilot with a smaller bit only if the tile and fixing instructions allow it; each extra pass creates another chance to chip or crack the tile.
Ease off as the bit breaks through. A sudden push can spall the back of the tile or drive the bit into the material below. Clear dust from the hole with a suitable brush or blower, keeping dust out of your eyes and lungs. If drilling into concrete, use eye protection and a properly fitted respirator; silica dust is hazardous. Don’t use water unless the tool, bit and roof conditions make wet drilling safe.
Common problems and fixes
The bit skates across the glaze: Stop before it scratches a wide arc. Try a purpose-made tile bit or a bit with a suitable sharp centring tip, and begin at low speed without hammer action. Don’t use a nail punch to make a deep dent; the impact can crack the tile.
The tile chips or cracks: Check whether hammer mode was on, the bit was dull, pressure was excessive, or the hole was too close to an edge. There is no dependable universal minimum edge distance for every tile and anchor. Follow the fixing maker’s guidance and leave enough material around the hole; when the location is constrained, consider another fixing point.
The hole is dusty and the bit stops progressing: Withdraw the bit periodically to clear dust. A blunt or overheated tip cuts poorly, and forcing it can enlarge the hole or damage the tile. Replace a worn bit rather than trying to compensate with more pressure.
The fixing spins or pulls loose: The hole may be oversized, dusty, or drilled into a substrate unsuitable for that anchor. Clean the hole and use the specified fastener and drill diameter. A roof tile itself is not a dependable anchor for a load; the fixing should engage the appropriate structure or masonry beneath it, with a detail that keeps the roof weather-tight.