ESEvery coring crew hits rebar eventually. The difference between a ten-minute pause and a destroyed core bit is whether the operator recognises what is happening in the first few seconds and stops pushing.
How to tell you have hit steel
Diamond does not cut steel the way it cuts concrete. The bit slows abruptly, the sound changes from a steady grind to a higher-pitched squeal, and the water coming out of the hole changes colour — grey slurry turns dark or takes on a metallic sheen.
On dry coring, the tell is sparks at the kerf and a sudden jump in motor temperature. On wet coring, watch the slurry and listen. An experienced operator hears rebar before seeing it.
What forcing does to the segment
Steel does not abrade the bond matrix, so the diamonds stop being exposed. The segment face polishes, friction rises, and heat builds in the bit barrel. Continue pushing and you get one of three outcomes: a glazed bit that will not cut concrete afterwards, a segment that cracks from thermal shock when the water hits it, or a stalled motor with a loaded clutch.
None of those are recoverable on site in the way operators hope. A glazed bit can sometimes be dressed, but the time lost usually exceeds the cost of moving the hole.
The immediate response
- Release feed pressure immediately. Keep the bit spinning and keep water flowing.
- Let the bit clear the steel with light pressure if the rebar is thin and the hole is already most of the way through.
- If the bit stalls, stop the motor, withdraw, and inspect the segment before restarting.
- Do not increase pressure to "push through". That is the move that ends the bit.
Relocate, resize, or cut
Relocating is almost always the least expensive option. Shift the hole by one bar spacing, or move it far enough that the new location clears the bar by at least a bit radius. On a layout where the hole position is fixed by a pipe or anchor, a slightly smaller bit plus a second overlapping hole can sometimes thread between bars.
Cutting rebar is a structural decision, not a drilling decision. In a slab, a single cut bar may be acceptable; in a shear wall, a beam, or a post-tensioned element it usually is not. Post-tensioned slabs are the case to stop on entirely — cutting a tendon is a serious incident, not a delay.
Where cutting is permitted, use a rebar cutter or a dedicated metal-cutting method rather than grinding through with the core bit. It is faster, cleaner, and does not ruin the segment.
Scan before you drill
Cover meters, magnetic locators, and ground-penetrating radar all reduce the odds of a surprise. A cover meter is cheap, fast, and enough for most slab work: mark the bar grid on the surface with chalk before setting the stand.
Scanning is not perfect. Bars run in two directions, spacing varies, and a scan that reads one layer may miss a second. Treat the scan as guidance and the first centimeter of cut as confirmation.
Drilling a hole that already contains a bar
If the bar is exposed in the hole and the hole must continue, options narrow. A smaller bit can sometimes pass beside the bar. A diamond core bit can cut a bar, slowly, at the cost of segment life. Drilling past the bar and then breaking out the core is another route, though it leaves a stepped hole that needs patching.
Whichever route you take, document it. A hole that cuts reinforcement should be recorded for the engineer, not quietly filled.
Bit and setup choice
For reinforced concrete, start from the diamond drill bit category. A turbo segment core bit with a protection tooth is a reasonable general choice, and an M14 sintered core bit suits smaller diameters where the risk of meeting a bar is higher.
Two related reads: drilling speed and pressure, and hole saw troubleshooting for the symptoms that look like rebar but are not.
Safety
Rebar contact raises the risk of bit binding and machine kickback. Use a stand with a vacuum base or anchor where possible, keep hands clear of the barrel, wear eye protection and hearing protection, and control water or dust. If the bit binds, release the trigger before attempting to free it — never lever a running bit out of a hole.
Tell us the slab thickness, bar spacing, and target diameter and we will confirm a bit specification that gives you the best chance of clearing the grid.
