What to do when you hit rebar
Stop. Reinforcement is a structural question, not a drilling one.
Recognising it
Drilling slows abruptly, the sound changes pitch, and you may see bright metal particles in the spoil.
Progress can stop almost completely while the tool still sounds like it is working.
Do not force it
A masonry bit is designed to fracture brittle material, not cut steel. Forcing it destroys the carbide, generates heat, and enlarges the hole.
Cutting rebar is not your call
Reinforcement is structural. Cutting it can compromise the element. Rebar-cutting bits exist, but using one requires the structural engineer's agreement.
The usual correct answer is to stop, move the hole slightly, and re-scan.
Avoiding it next time
Scan before drilling with a rebar locator or cover meter.
On precast, work from the reinforcement drawings — see cast-in-place vs precast.
Questions about this
Can I just drill through the rebar?
Not without authorisation. Reinforcement is structural, and cutting it can compromise the element. Rebar-cutting bits exist but using one requires the structural engineer's agreement.
How do I avoid rebar in the first place?
Scan before drilling with a cover meter or rebar locator, and on precast work from the reinforcement drawings where they are available.