Basement floor, hollow???

andy1978December 2, 2007

A small spot (3'x3') in my basement floor (concrete slab) sounds hollow. When I tap on the floor with a wood block, most of the basement sounds solid, but this one area sounds like it is hollow. There are no sewage lines under the house, that I know of. Should I be concerned with this? If so, what should be done about it?

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Isn't this a scene in the Poltergeist?

Seriously, there may well be voids between the concrete and the underlying material. Especially if it was not compacted and/filled with compacted gravel. This is usually not a cause for concern unless you're putting some extra heavy item in the basement--a pool for instance.

If this is a very old house, you never know. An acquaintance was having the basement on a 19th C. home lowered. A workman using a jackhammer to break up the floor suddenly felt the hammer slide away into a well that he had broken into.

    Bookmark   December 2, 2007 at 8:37PM
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If you don't have any water intrusion or cracking it's probably just a void, and nothing to worry about. If you're nervous that it's a big hole that might collapse, you could always get a masonry bit and drill down to see how thick the slab is at this point; this would also allow you to shove a wire in to see how deep the hollow spot is. After you're done exploring. caulk the hole.

On the other hand, there is wisdom in the old saying: "If it ain't broke, don't fix it."

    Bookmark   December 4, 2007 at 8:33PM
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