Honeycombs are generally voids and hollow spaces (you can see in the image above) occurs where concrete could not reach. Honeycombs are also occur inside the concrete mass which we cannot see with naked eye.
However the small hollow spaces are cosmetic but the deeper areas may lead to rusting of reinforcement inside concrete which reduces the durability and strength of the structural member.
3 Main reasons of honeycombing
- Insufficient fine material in concrete mix
- NO covering to reinforcement bars
- Not Vibrating properly.
Below images showing honeycombing in different structural members.