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In pulling off some broken mortar on the dirt foundation (where the actual brick footers rest) of a 1920's house crawl space, I discovered a layer of black coal just under the mortar. There are chunks of it, and some smaller particles.

Was coal ever used as an insulator? Why would the original builder install a layer of coal below the mortar?

a coder
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    I've never heard of a dirt footer. This entire foundation might be a bit of a home made 'use whatever we have laying around' thing. Back in the 20's lots of builders WERE the homeowners and used what they had. – DA01 Jun 18 '12 at 18:51
  • @DA01 -- the dirt footer is the mound that the actual brick footer sits on. I may need to rephrase my question to avoid confusion. When the house was built, or some time after, they dug out the area under the house and made it a walk in crawl space. The shoulders of clay were left and covered with a thin layer of mortar. – a coder Jun 18 '12 at 19:19
  • Where do you live? I've never heard of such a foundation before. I'd be a bit wary of the entire thing, but perhaps it makes sense given your region. – DA01 Jun 18 '12 at 19:26
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    Maybe the builder was trying to make diamonds. – Tester101 Jun 18 '12 at 20:26
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    My grandfather used to feed pigs coal to get rid of parasites - and coal tar (creosote) has historically been used as a pesticide on wood poles. Perhaps that is somehow related... – Mark Schultheiss Jun 18 '12 at 20:31
  • oh, and I forgot to mention that naphtha comes from coal and that is mothballs bascially – Mark Schultheiss Jun 18 '12 at 20:40
  • Insulation? Never heard of that one, I have been told it was used as filler. – Gunner Jun 18 '12 at 21:49
  • My grandfather used coal for heat and when it was delivered it was piled up not far from his house. Maybe the is where somebody kept their coal kept? It could have been mortared over after they switched heat source. – lqlarry Jun 19 '12 at 02:39
  • lqlarry - that is a possibility. The coal bits appear to only be in one corner of the crawl area. Very likely that is what is happened. – a coder Jun 19 '12 at 13:02

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Coal (especially in cities above a certain latitude) was stored under houses, often delivered down a chute to be handled as little a possible as it is messy & dusty.The cost of removing the leftover coal (an unpleasant job) far exceeded its value, so it stayed, often getting covered up later to stop the dust. Heating oil & tanks today face a similar $ dynamic in houses changing to gas, geothermal, electric, etc.

Mc guiver
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