Diamond core bit drilling through rebar in reinforced concrete

Coring Through Rebar: How to Drill Reinforced Concrete Without Wrecking Your Core Bit

Ask any coring operator where they lose the most time and the most money, and the answer is almost always the same: rebar. A core bit that sails through plain concrete can stall, glaze, or stop cutting entirely the moment it hits a bar of steel. Understanding why that happens — and how to keep the bit cutting through it — is one of the biggest levers you have on your cost-per-hole. Hitting steel is not the exception on most jobs; it is the job. Reinforced concrete is designed to be full of rebar, so the real skill is drilling through it without destroying the bit.

Why Rebar Punishes a Core Bit

Concrete and steel want opposite things from a diamond core bit. Concrete is abrasive: it wears the metal bond down steadily, which is exactly what you want because it keeps exposing fresh, sharp diamonds. Steel is the reverse — it is tough and gummy, it does not abrade the bond, and it work-hardens under the bit. When the segment stops wearing, the diamonds stop being exposed, the exposed diamonds polish flat, and the bit glazes over. A glazed bit rubs instead of cuts, heats up fast, and can be ruined in a single hole if the operator keeps forcing it.

This is why the same bit behaves like two different tools depending on what it is in. The goal when coring reinforced concrete is to keep the bond eroding enough to keep the diamonds sharp, even while the segments spend part of every rotation grinding through steel instead of aggregate.

Wet coring is not optional here

When you are cutting steel, heat is the enemy, and water is how you fight it. Running a wet bit such as the CD200 PRO wet core bit flushes the steel cuttings out of the kerf, keeps the segments cool as they work-harden the bar, and controls silica dust from the concrete at the same time. Adequate, continuous water — fed reliably through a water distributor — is the single biggest thing keeping your bit alive when it is in steel. If the water stops, the bit is usually the next thing to stop.

Technique: Getting Through the Bar

Rebar rewards patience and punishes force. The instinct when a bit slows in steel is to push harder; that is exactly what glazes it. Instead:

Ease into the bar. As the bit contacts steel, back off pressure slightly and let the diamonds work rather than shoving them into a surface that will not abrade.
Keep it wet and keep it turning. Never let a loaded bit dwell in one spot in steel — that is how heat builds and diamonds polish.
Watch for glazing. If penetration drops off and the bit starts to squeal or smoke, stop and dress the segments on an abrasive block or a dressing stick to re-expose the diamonds before continuing.
Let the rig hold alignment. A wandering or cocked bit binds on the bar; a rigid, well-anchored setup keeps the cut square so the segments share the load.

Choosing the Right Bit for Reinforced Work

Not every core bit is built for a steady diet of steel. Bond hardness and segment quality decide how well a bit holds up when it is cutting rebar as much as concrete. A general-purpose bit like the CD100 wet core bit handles routine holes economically, while a premium barrel is where the difference shows on heavily reinforced work.

Consideration	Light rebar / general concrete	Heavy rebar / continuous steel
Recommended bit	CD100 (economical, versatile)	CD200 PRO (premium barrel & segments)
Bond behavior needed	Balanced wear on concrete	Keeps exposing diamonds through steel
Water demand	Standard wet flushing	Maximum, uninterrupted flushing
Operator pace	Steady feed	Patient feed, ease through every bar
Cost-per-hole driver	Bit price	Segment life & holes completed per bit

On a job that is mostly steel, the cheaper bit is rarely the cheaper choice. A premium bit that finishes many more holes before it wears out — and glazes far less — almost always wins on cost-per-hole, because the real cost is not the barrel, it is the time lost to a stalled hole and a ruined bit. Match the bit to how much steel the job actually contains.

Bottom Line

Rebar does not have to be a bit-killer. Keep the water flowing, ease through every bar instead of forcing it, dress the segments the moment they glaze, and match the bit's bond to how much steel you expect. Do those four things and reinforced concrete becomes just another hole — drilled clean, on the first bit, at a cost you can predict.