What is Concrete Honeycombing?

While Honeycombing of concrete can look like it is being attacked from some sort of creature or chemical, that is rarely the case except in decorative concrete flatwork where the surface has been “released” to reveal the larger aggregate.  This is done beesdeliberately by washing the surface with mild etching compounds prior to curing of the concrete surface.  It is certainly never the result of bees and the honeycombs associated with them.

When concrete is poured into the foundation forms it does not just flow in like water and fill up the forms to the top.  If it is not vibrated properly it may leave voids called “honeycombing.”  The exposed aggregate leaves a honeycomb look and hence the name.  This first picture is of honeycombing in a footing.

Honeycombing of concrete

Honeycombing of concrete footing

The heavier aggregate is left exposed with very little cement, sand and smaller aggregate that would normally surround the larger aggregate if it had been properly “settled.”  This condition is more an indication of poor workmanship than it is a serious structural defect.  Severe honeycombing could become serious if it is extensive enough—-but this is pretty rare.

When I was a kid I often had the job of hammering the sides of the forms to help vibrate the concrete into place.  In modern construction there are “stingers” to do the same job.  They look like a long hose with a salami on the end that is inserted into the wet concrete while it is being poured.  The thing vibrates like a BarkaLounger gone wild!

The honeycombing in the following picture is about as extreme as I ever seen it and yet it is still unlikely to be a major structural concern—-even with the exposed rebar.  The structural engineer will likely advise patching or nothing at all depending on how likely it is to pose a problem.

Severe Honeycombing

Severe Honeycombing

So why is this not likely to be a major structural concern even though it looks really nasty?

Well look at it this way—-the entire defect is about 16 inches long and about 4-5 inches tall—-still much smaller than any foundation vent that might be installed in the same wall.

This kind of defect can easily be patched to prevent moisture intrusion and vermin entry to the house structure.

Proper patching will even keep out the concrete eating bees. concrete eating bees?

 

Charles Buell, Real Estate Inspections in Seattle

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