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Natural stone is harder to drill than brick or many concrete blocks, and it varies from one piece to the next. A bit that works in soft limestone may stall or overheat in dense granite. For most jobs, choose a carbide-tipped masonry bit for occasional holes in softer stone, or a diamond bit for repeated holes and dense stone. Match the bit to the drill, the hole size and whether the stone can tolerate impact.
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Choose the bit for the stone and hole
For small holes in limestone, sandstone and some slate, a conventional carbide-tipped masonry bit is the economical choice. It cuts with a blunt carbide tip and works well in a hammer drill when the stone is not especially brittle. A basic set is suitable for occasional holes for masonry screws or small anchors, but expect slower progress and more wear in hard stone.
For granite, dense basalt, hard quartz-rich stone or a long run of holes, use a diamond-tipped bit. Diamond grit grinds the material rather than relying on a carbide edge to chip it. These bits cost more, but typically last longer in hard stone and are less prone to losing cutting performance from a chipped tip. Look for a diamond masonry bit in the exact diameter and shank style your drill accepts.
| Bit type | Best suited to | Drill setting | Main trade-off |
|---|---|---|---|
| Carbide-tipped masonry | Occasional small holes in softer stone | Hammer mode if stone is sound and not brittle | Affordable, but slower and shorter-lived in dense stone |
| Diamond-grit bit | Hard stone, cleaner holes, repeated drilling | Usually rotary-only; follow the bit maker’s instructions | Higher upfront cost; many need cooling |
| Diamond core bit | Larger diameter holes | Rotary-only unless explicitly rated otherwise | Needs careful alignment and often water cooling |
Check drill and shank compatibility
Most standard masonry bits have a round shank and fit a three-jaw chuck. Larger bits may use SDS-Plus shanks, which require an SDS-Plus rotary hammer. Do not buy an SDS bit for a regular cordless drill unless you have a suitable chuck adapter; adapters add wobble and are a poor choice for accurate holes.
A hammer drill is useful for carbide masonry bits in sturdy stone, but hammer action is not automatically better. Percussion can crack thin slabs, split stone near an edge or damage a polished face. Diamond bits generally cut by abrasion, so use rotary mode unless the manufacturer specifically permits hammer action. A carbide masonry bit set is a sensible low-cost option for mixed, occasional work; for dense stone, buying one quality bit in the needed size is often better than a large bargain set.
Get the diameter and depth right
Choose the bit to match the anchor or fastener instructions, not just the screw diameter. Masonry anchors commonly specify a hole size; follow that measurement. An undersized hole can prevent the anchor from seating, while an oversized or ragged hole can leave it loose. For a masonry screw, use the manufacturer’s specified pilot diameter and embedment depth.
Measure the required depth and mark the bit with tape, or use a depth stop. Drill a little deeper than the anchor’s embedment—often about 6 mm (¼ inch)—to leave room for dust, unless the anchor directions say otherwise. Before drilling, check for hidden wiring or plumbing and keep holes away from unsupported edges. As a practical precaution, leave at least several bit diameters between a hole and a stone edge; brittle slabs may need more.
Drill without overheating or chipping
Mark the location with a pencil or removable marker. On polished or smooth stone, a small piece of painter’s tape can help the bit stay put, but it will not prevent cracking. Start at low speed with light pressure. Once the bit has established a shallow seat, increase speed only as needed; forcing the drill is a common cause of overheating, wandering and broken carbide tips.
For a carbide bit in suitable stone, use moderate pressure and let the hammer mechanism do the work. Pull the bit out every few seconds to clear dust, especially in deeper holes. If progress slows, the bit is getting hot or the hole fills with powder, stop and clear it. For a diamond bit, follow its cooling instructions. Many small diamond bits are designed for wet drilling; others are rated for dry use. Never add water to a bit or drill that is not designed for wet work, and keep water away from the drill’s motor and battery contacts.
If the stone is thin, valuable or prone to cracking, disable hammer mode and use a diamond bit in rotary-only mode. Start slowly, support the stone fully and avoid drilling too close to an edge. A chipped entry is often caused by starting too fast or letting the drill tilt; a breakout on the far side can be reduced by slowing down as the bit approaches the back surface.
Know when the bit is done
A dull bit produces fine dust but makes little progress, needs more pressure, or discolors from heat. Continuing can enlarge the hole, overheat the drill and damage the stone. Replace a carbide bit if its tip is chipped or visibly rounded. Diamond bits can also wear out: a glazed cutting surface that no longer grinds is a warning. Some manufacturers recommend dressing a glazed bit on an abrasive material, but follow their instructions rather than improvising.
For one or two anchor holes in soft stone, an inexpensive carbide bit is usually enough. For hard granite, repeated holes, or a clean hole in a visible surface, a properly sized diamond bit is the safer purchase. The best result depends as much on choosing rotary or hammer mode correctly and clearing dust as it does on spending more for the bit.