Honeycomb and larger surface voids require procedures resembling those for typical concrete repairs. But there’s nothing typical about the recommended approaches to repairing these voids. They vary greatly.
While repairing voids or honeycomb in concrete surface, the most common question that arises is what should be the thickness of the repair. Some agencies do not require a minimum thickness, while others set limits, such as 1 inch or 2 inches (25 mm to 50 mm). Some suggests using an epoxy as bonding agents while other suggests using of cement grout.
In any case, good concrete repair practice calls for removing any loose material within the void. According to scientists, honeycomb often contains loose coarse aggregate if the void is caused by a leak in the form. If the void is caused by poor concrete consolidation; the coarse aggregates often are intact.
Procedure to Repair Honeycomb in Concrete
Use light chipping hammers weighing approximately 7 kg or less to remove the required amount of concrete, because impact hammers can fracture the surface of the concrete that remains. Follow chipping with sandblasting or water blasting to remove this fractured surface.
A common way to place the repair material is to simply trowel it into the void. But Glenn Smoak (author of the book Guide to Concrete Repair) contractors can achieve better results using a small pneumatic mortar gun to apply a grout similar to hand-applied dry pack. (as shown below)
A suitable mix contains 1 part Portland cement and 4 parts sand and has a water-cement ratio of about 0.35. If the repair is deeper than 1 inch (or 25 mm), apply the mortar in layers no thicker than 3⁄4 inch to avoid sagging and loss of bond.
After placing each layer, wait about 30 minutes before placing the next layer. You don’t have to scratch or otherwise prepare a preceding layer before placing the next, but do not let the in-place mortar dry.
To complete the repair, overfill the void slightly. After the material has hardened slightly but can still be trimmed off with the edge of a steel trowel, shave off the excess material, working from the center toward the edges. When finishing the repair, exercise extreme care to avoid impairing the bond.