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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  1. May I use your explanation on our website? FoxInspectionGroup.com in Houston, Texas. I would, of course, link to your site. Thank you for your consideration.

  2. My 85 yr old mom had a sudewalk installed. The sides have openings and the contractor said he can fill them in and not to worry about the integrity of the concrete. Should i worry?

  3. Hi, This is a picture of a wall that it probably 25 feet high.

    They patched it but is it a structural concern? The wall is a retaining wall against a hill.

    Also notice the horizontal line. If you can zoom in you see the rebar. The patched this as well.

    Oh, and did I mention this is in Mexico…


  4. I am not an engineer. The closest I came to be an engineer was my dad who was one. Oddly I did work at Autodesk (AutoCAD) corporate HQ for 15+ years but in Systems Finance…

    I have a question. I purchased a condo in a 8 story building in Mexico that is being built now. I couldn’t help but notice a problem (to me) and wanted to see if a structural engineer thought this was a problem or not.

    In this picture, concrete was patched. I was curious what it was and then found the next picture.
    [img http://res.cloudinary.com/engineering-com/image/upload/v1516949626/tips/pic1_xrkolx.jpg%5D

    Here you can see a big piece that is missing and the exposed re-bar. Maybe when they pulled the form off a chunk fell of or maybe the concrete didn’t settle. I don’t think they would arbitrarily remove it. Also the horizontal line is showing exposed rebar. Again it was patched.

    My question, is this a structural problem? The total wall height is some 50 feet and this is at the bottom of the wall. And is patching it with concrete okay? Also curious what those pieces of re-bar that are hanging out of the wall are for? I just want to make sure. It is Mexico after all although the engineering company and construction company work on big projects.

    Thank you in advance!! I really appreciate it.

    [img http://res.cloudinary.com/engineering-com/image/upload/v1516949801/tips/pic2_fhzhxs.jpg%5D

  5. Hi Charles,

    Can I get your take on the honeycombing in the attached photos? There are numerous areas throughout the external foundation and basement interior that have some exposed aggregate, but most patches are no bigger than my palm. The pictured area here is by far the largest, and a similarly sized area exists just on the opposite side of the foundation in the basement. Some aggregate chunks were loose and could be wiggled out.

    Do you think this could be a structural issue or is it more of a cosmetic issue as your post suggests? The home in question is about 100 years old in NW Seattle.


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