A friend of mine was working in an old basement and busted up part of the slab. He discovered that the slab was quite thin (1″ thick no big surprise there) but that the gravel under it appeared to be anthracite coal. I have yet to hear the results of the “burn a piece of it” test.
Has anyone else seen coal used under a slab in old construction? Seems like a poor substrate – brittle, organic, and prone to crushing, but likely cheap and plentiful when the thing was poured.
ArcSol
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Maybe the builders hoped their future decendants would return and find diamonds?
Since the slab was "cheaped out" at 1", maybe the builder just put whatever was laying around at the time.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Most old houses had dirt floors and many burned coal. After an owner replaced a coal furnace with one that burned a "modern" fuel, the leftover coal was often left in the coal bin in the basement. Probably a homeowner who wanted to cover over the dirt floor just spread out the coal and placed concrete on top of it.
We busted though an old slab in Durham NC and discovered the fill was fly ash coal cinders from the local steam plant, very messy and dusty but had been supporting the slab for many years we had to tunnel under it to install a new AC duct and it was a nasty mess but fairly easy digging.
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