Concrete Honeycombs are gaps in the concrete wall. The problem occurs when the concrete wall is poured from the concrete truck into the forms. Gravel and concrete mix doesn't always mix properly, causing gaps in the mix, when it is poured. The gaps remain and the concrete hardens. Honeycomb in poured concrete walls are not a common issue that can cause basement leaks. If the honeycomb goes through to the other side of the wall, leaks can occur in the honeycomb, causing possible water damage and mold. This can be repaired by a number of different methods by a trained technician.