As experts I'd like to ask your opinion on a building technique. I saw plans for a very simple building using earth directly from a to-be pond with a mechanized digger and putting it in a half-circle (or square with one opening) by building the walls, compressing each layer with the machine.
Then on top simply build a roof with wood (or tree trunks) by simply laying them on top of the earth, building the rest of the roof from there, possibly covering the whole thing with earth again. My question to you is: do you think earthen walls build this way will hold the roof that way?
I'm sure cob would do so, but I'm talking (compacted) earth, which would obviously be much faster to build.
Sepp Holzer uses a similar technique for his 'stables', building a room into the mountain, but obviously that's not the same as building earthen walls on flat land and putting a roof on there. Also this idea came from Geoff Lawton who claims to have put this into practise, but I can't find any examples of how.
I guess the consistency of the earth matters, but even clay or loam would be prone to erode. But then again if the roof covers the earth walls, there shouldn't be too much danger. Also they can be very thick without much problem.
I'm not sure how you'd get near-vertical inside walls while compacting with a mechanical digger... I suppose after compacting a mass you could dig the inside vertical. Unless you can get those vertical walls, you would have little floor space without a significant roof span, and wood directly in earth, unless a wide watershedding roof was added, would have a pretty short safe lifespan. For a very dry region I could see it being viable.
That house Geoff was talking about in his online PDC course was for a previous PDC student who only had a couple of grand$, and wanted to build the cheapest dwelling Geoff could come up with. indeed the clay from the dam dumped on the uphill side of dam and compacted with the excavator I think he said it was a 30 tonne. Then they cut the walls out vertically with the digger then put a roof on it. Then enclose the front, it sounded like more of a shack than a house.
But similar concept to rammed earth on the inside.
Bill Mollison talked a bit about this kind of building in one of the PDC vids. He said he got it built in 3 days. Unfortunately the vid series seems no longer to be on youtube.
I've just found it on my computer (vid 34 Housing part 2)... he built it in Buckan, I think he said, don't know where that is (Australasia? I think that's where the PDC was). He excavated a dip in the ground to get some soil and laid it nearby to give a raised floor. He continued excavating and built up a compacted earth circular wall as you would a dam wall, rough cross section like the letter "A" but not so pointed. He put on the top of the wall what he calls a siller (?) which seems to be a narrow load bearing platform which forms a ring sitting all the way around the top of the wall. He doesn't say what it's made of. Wood? Stone? Brick? This sits firmly as the wall is compacted. He built a pillar in the centre and put the roof on. He didn't say what it was made of. I guess some kind of framework with some kind of paneling ... corrugated metal? ... because he said some of the panels were transparent ("Laserlite" - polycarbonate) to let in light (and grow veg underneath on the walls). Obviously a good door is needed! He describes a moat around it, created when excavating the earth, which is connected to a "well" - an access to the moat water - within the house via an underground channel. Fish in the moat, feed the fish via the well. He says it's suitable for any climatic zones, cost about 2000 - 3000 dollars (Aussie I guess). Flood proof.
I think this would very much depend upon how you're looking to layer up using a digger and compact it, how much time you're looking to take to build it, what kind of dirt you're digging, and what the atmospheric conditions are like in the location.
You can't just put dirt on top of dirt, stick a couple of tons of digger weight on it and expect it to solidify into a squared off wall. What you'll have in that case is a bucket shaped divot in the middle of the bit that you wanted to be a wall. Looking into solidified rammed earth building historically, they'd use a series of molds, which were flat plates held a set distance apart by long bolts (2 or 3 at both top and bottom), to bring the wall up a section at a time. You'd tip the earth into those molds and use a manual packer to ram the earth down inside them, keep filling and packing until each section was full, then shift the plates up one bolt and continue the process. Ideally, you'd take the plates off and give each section time to dry out and strengthen before you added any more earth on top of it.
If you want to knock up something like that quickly then you may be able to do something similar using the right kind of dirt and the right kind of pallets. Build up walls, a layer at a time, with pallets which are largely covered top and bottom, and set them up so that you can drop sloppy dirt down between the batons so that it will fill the entire depth of the pallet, then "plaster" the inside/outside of your pallet frame as it dries out.
I originally thought that your "earth from a pond" was stuff that was from the bottom of a pond rather than earth that you're digging out to form a pond. Having ducks, and having to dig out the same pond on a regular basis since they keep filling it up, the kind of stuff that comes out of the bottom of *that* pond is absolutely great for forming solid walls - even if ours is on a hugel bed.
He didn't give details, just saying "as you would build a dam". So maybe with the right amount of water added? I know they build dams by hand in India without formers by pummeling damp earth bit by bit. There must be a way to do this with an excavator more quickly if Bill did it in a couple of days. He also mentioned building walls with formers using 1 part mud and 1 part lime made into a sloppy consistency with water and adding just over 1 part "grass" (?) then building up in layers of less than 2 feet for a glass-like wall, and they also discussed using cob to build houses.
"Rammed earth" is a well known, tried and true building method. I've helped in designing and building, and living in, rammed earth buildings for the past 25 years. It provides excellent thermal mass, and a lovely ability to temper humidity and sound. It has good compressive strength and can hold up a heavy roof or second story, but is not considered appropriate for a retaining wall (ie having earth piled or banked against it), nor in any situation where it could possibly get thoroughly damp. In other words, it's great for free-standing walls that are not buried.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.
Completely depends on soil and climate. It will work lots of places if you add stick to the walls and roof or tarp the entire mound.
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