where does "coal dust" come from?

October 16, 2007 7:14 PM

In many old houses once you break through the lath-and-plaster (or it breaks on you and you need to repair it) there is a disgusting amount of "coal dust" that comes out. Where do these carbon particles come from? Yes old houses used to be heated with coal. But I assume the furnaces had chimneys to vent the combustion products. So why is there so much dust within walls and ceilings?
posted by MonkeySaltedNuts to home & garden (21 comments total)

Yes, and that is the coal dust from the old coal used for housing heat (and also from industrial coal burning - you might live in a town that had a lot of nineteenth-century manufacturing, or along a train line).

Coal was an absolute blight on American homes, cities, and lungs. The coal dust got everywhere and settled everywhere. It was in people's clothes and in their eyelashes. It blew and gusted in the air of any thickly settled town. It grayed clothes on clotheslines and settled on animals. Archaeologists today find measurable black bands near the surface of compacted soil, layers of coal dust below twentieth-century fill. Industrial towns have enormous deposits of this dust where coal was once piled. People who never approached a mine had lung ailments, and dusting every day was a necessity.
posted by Miko at 7:32 PM on October 16, 2007 [2 favorites has favorites]

This is pretty good.
posted by Miko at 7:34 PM on October 16, 2007

You didn't really ask that question, but the answer is that it wasn't the combustion of the coal that created the dust, it was the storage and transfer of the coal.

The coal burned in the furnace was delivered to the house in an open cart, shoveled into the basement in a giant pile to last several months, and then shoveled load by load into a hod, which was then shoveled into the furnace, a few times a day.

All the abrasion of the coal chunks on one another caused the small coal particles to scrape off and become airborne.

In industrial areas, the four-story-tall coal mounds in factory yards, feeding hungry furnaces endlessly, and the coal mounds in housing-supply companies, sent constant new loads of particularized coal into the air. Coal was moved several times a day, every day, and with each transfer, clouds of new dust were released into the air.

So it's even possible for homes that never had coal heat to be saturated with coal dust. It just got everywhere; it was a fact of nineteenth-century life.
posted by Miko at 7:55 PM on October 16, 2007

I think "The coal dust got everywhere" was the portion of that which answered your question. Do you think the insides of your walls are hermetically sealed? Even if they are pretty well sealed, small amounts of coal over time will add up, since nobody ever dusts inside the walls.
posted by blenderfish at 7:55 PM on October 16, 2007

And in other words (because you might ask this next) it's only in the walls and ceilings because coal dust went everywhere, but the residents cleaned the houses' exposed surfaces regularly, so the only place it could hide and accumulate over long periods of time would be in the cracks of the walls, floors, and ceilings where it slowly settled over time.

Coal dust could get into a completely sealed-for-the-winter house. It's incredibly fine and was carried on the air all the time.
posted by Miko at 7:57 PM on October 16, 2007

I have refinished 2 houses (one 1870, one 1892) right down to the plaster. They were plenty dusty, but it wasn't all coal dust.

You may have a house that was constructed "balloon" style, where there is lots of space in the walls for dust to travel around in. You might be in a spot that was near the old coal chute of the house, and some of the coal dust blew up into the walls. But it's hard to say for sure.
posted by kuujjuarapik at 7:57 PM on October 16, 2007

Miko, your link was very interesting, I thought it answered the op's question.
posted by JujuB at 8:00 PM on October 16, 2007

The coal dust got everywhere and settled everywhere.

That makes perfect sense to me; I didn't read a rant into Miko's answer at all. Even with chimneys that dust was apparently super-pervasive. Once inside the walls/ceilings, there would have been less disturbance (no breezes emanating from within for example), and so it would be pretty trapped. Fast forward years and years of buildup and voilà, all the crap comes pouring out when you break through.

Just a speculation.
posted by Stewriffic at 8:00 PM on October 16, 2007

Uh... MonkeySaltedNuts if you don't like Miko's answer, why don't you ask for a refund? Oh, that's right, you haven't paid anything for his answers...

I think Miko's point is that coal dust goes everywhere... even inside your walls. (Also, his friendly comment is hardly a rant - in fact, I think you owe him an apology...) Further because we no longer heat our homes with coal its easy to forget just how messy the stuff is...

Getting back to your question... Think about it: air certainly circulates within your walls. Coal dust, which can be incredibly fine, is carried on the air... ergo it winds up wherever the air goes... It's not like the space between the walls in your old house is air tight or anything.

Further, in older homes coal was dumped (rather violently) into the basement where it would be stored for later use. Over the decades basements would become completely black from the presence of coal in one corner. The coal was used to fire the furnace which in many cases would create updrafts that carried the coal dust through out the house via small drafty cracks in the ceiling joist, floor rafters, and other points of entry. When you consider that this type of usage went on for decades (perhaps even a century or more in some homes) its easy to understand how coal dust makes into every corner of a home - even into the attic.

Anecdotally I lived in downtown Norfolk Virgina a few years back and I would routinely find a fine coating of coal dust throughout my apartment anytime I left the windows open. Turns out that Norfolk is major port of exit for domestic coal bound for Europe... the coal dust was drifting on the wind many miles downstream from the port and into my apartment!
posted by wfrgms at 8:02 PM on October 16, 2007

Yeah, I was making an honest effort to answer your question because this is something I know about through my work. I'm sorry if it came off as a rant - it was meant to be enlightening as to why coal dust is still found in old houses.
posted by Miko at 8:14 PM on October 16, 2007

Another thing to consider is that the asphalt dust from old roof shingles looks very much like coal dust and can be copious. It goes everywhere from the attic on down inside the walls until something stops it.
posted by kuujjuarapik at 8:21 PM on October 16, 2007

"So why is there so much dust within walls and ceilings?"

Even your average tract house built today can have as much as a couple complete air exchanges per hour between inside and outside during heating season. Pre WWII houses are ridiculously drafty. They had no air barrier at all (stucco was about as good as it gets and that wasn't very) and no vapour barrier. Wind literally blows right thru the wall along with any dust it may be carrying. Dozens of complete air changes every hour. That breeze, helped along by the air velocity change in the wall cavities, would deposit dust inside the walls. The dust is often held in place once it settles by moisture. It often starts to be actual dirt rather than dust (though that may be a function of the clay content of the soils around here). I've seen as much as an inch of dirt/dust inside the exterior wall of a tar paper and clap board covered 150 year old house.

In places where coal was common the most noticeable dust is going to be the black coal variety.

It's pretty wild to pull up an old hardwood floor where the installer placed sheets of newspaper between the sub floor and the hardwood and then observe a distinct dust layer even in between sheets of paper.
posted by Mitheral at 8:36 PM on October 16, 2007

Oh and I think Miko is a her, not a him... sorry!
posted by wfrgms at 9:07 PM on October 16, 2007

Anecdotally I lived in downtown Norfolk Virgina a few years back and I would routinely find a fine coating of coal dust throughout my apartment anytime I left the windows open. Turns out that Norfolk is major port of exit for domestic coal bound for Europe... the coal dust was drifting on the wind many miles downstream from the port and into my apartment!

Funny, wfgmrs, I was about to reference living in Norfolk too. It wasn't just drifting from the port, though. Some of it is being carried via the coal cars from the trains.

People don't believe me when I describe wiping coal dust off of the furniture every week. It does teach you to regularly dust, though!
posted by desuetude at 9:13 PM on October 16, 2007

I asked this question because I asked it of a repair guy who was fixing the second floor ceiling of a 3 story house that had partially fallen out because of a rain leak.

His explanation was that the old chimney had leaks or that once the carbon particles flew out of the chimney gravity made them find their way back into the house. He also said that the "coal dust" problem got worse the higher in the house you went.

I don't accept his explanations for "coal dust" though I might accept his empirical observation that "dust" becomes worst at the top of a house if there were some quotable sources to back this up.

I really can't believe that the incredible coal pollution I have found of the interior spaces (inside walls and ceilings) is just the result of the dust of coal being dumped into the basement that has wafted up through the cracks.

One way to answer this question would be to give a college chemistry major some samples of the soot and ask him/her if it was combusted or uncombusted.
posted by MonkeySaltedNuts at 9:30 PM on October 16, 2007

You're overcomplicating it, MonkeySaltedNuts. My job is working with archaeologists, architectural historians, and preservationists with archaeologists in a preservation organization, and the coal dust is common. It's in all the houses in our post-industrial town. It's quite well documented. The chimney guy's explanation doesn't really hold.

The key point is that it wasn't just the coal dumped in your basement that created that much dust. There was that much dust coming from every basement in every house in the town, and from every business, every manufacturing plant, every train and steamboat that went through, and every distribution point and fuel company. The stuff was thick in the air, thick enough to blot out the sun on some days in some cities. It wasn't just one furnace that did this, it was tons and tons of airborne coal.

Christine Rider of St. John's University writes that "the old 19th-century industrial towns never became beautiful...for so long as coal was the predominant power source towns were dirty, smoky, and polluted."

In London, the smoke that billowed as a result of domestic and industrial coal burning began mixing with existing natural fog. Charles Dickens wrote in Bleak House that “smoke lowering down from chimney-pots, making a soft black drizzle, with flakes of soot in it as big as full-grown snowflakes –- gone into mourning, one might imagine, for the death of the sun.”[3] The resulting smog (word coined from smoke + fog), was often sited by both visitors and locals as an optical experience unique to London. These low-laying fogs reduced visibility in the city to less than a mile while resulting in the loss of up to fifty percent of the sunshine in the winter months.[4] Thomas Hardy mentions it is in his 1900 poem “The Darkling Rush” as


I leant upon a coppice gate,
When Frost was spectre-gray,
And Winter's dregs made desolate
The weakening eye of day.
The tangled bine-stems scored the sky
Like strings of broken lyres,
And all mankind that haunted nigh
Had sought their household fires.[5]

While writer Arthur Symons wrote that “In London, men work as if in darkness, scarcely seeing their own hands . . . and not knowing the meaning of their labour.”[6] French writer Joris-Karl Huyseman likewise wrote in 1884 that “A rainy, colossal London smelling of molten metal and of soot, ceaselessly streaming and smoking in the fog now spread out before his eyes . . . All this was transpiring in vast warehouses along the river banks which were bathed by the muddy and dull water of an imaginary Thames . . . while trains rushed past at full speed or rumbled underground uttering horrible cries and vomiting waves of smoke, and while, through every street, monstrous and gaudy and infamous advertisements flared through the eternal twilight.”[7] "

The Industrial Revolution of the eighteenth and nineteenth century only worsened the problem. Burning coal to produce electricity and fuel trains produced a dark cloud of smoke over every major center of industry in the world and covered entire cities with soot. To deal with this problem, engineers built higher smoke stacks to move airborne waste further away from the source. Regardless of how high the stacks got, the people down wind complained about the ashes and the acid gases from coal combustion (the source of acid rain) destroying their crops.
posted by Miko at 9:41 PM on October 16, 2007 [4 favorites has favorites]

Those last 3 that begin with links were direct quotes from the websites linked. Sorry I forgot to indicate that - everything below "Christine Rider' isn't my writing.
posted by Miko at 9:42 PM on October 16, 2007

MonkeySaltedNuts if the dust source was internal the stack effect would explain why more dust is found in upper floors than lower floors. Assuming it wasn't just selective observation.
posted by Mitheral at 9:50 PM on October 16, 2007

if the dust source was internal the stack effect would explain why more dust is found in upper floors than lower floors.

Not an answer per se, but a comment... I tore out half of the third floor of my Victorian semi last summer. Compared to the work I've done on lower floors, there seemed to be more dust on the upper floor.

ALso, I don't know if it was all coal dust - my house has various now-disconnected pipes for gas lighting. It could also have been carbon from burning gas inside the house - gas lamps don't always have 100% complete combustion. Or candles.

But per other posters, the walls on an old house are more of an air filter rather than solid walls. They keep our birds, but that's about it.
posted by GuyZero at 6:19 AM on October 17, 2007

While living in Beijing last year my wife and I had to dust our apartment twice daily even though it had new, modern, sealed, double glazed windows with additional storm windows.
posted by Pollomacho at 6:59 AM on October 17, 2007

MonkeySaltedNuts, why don't you go to ask.collegechemestrymajor.com then?

Seriously, everyone here has offered compelling answers to your rather pedestrian question and not only have you not said "thank you" you've dismissed all of our good answers while simultaneously complaining that weren't chem majors.

Screw you, I'm never answering one of your questions again...
posted by wfrgms at 7:52 AM on October 17, 2007