Of the three types of soil-home construction commonly used today (adobe, pressed block, and rammed earth), I prefer the rammed (or tamped) earth method. I suppose the reason for this is that after five years of living in a home built that way, I'm 100% pleased with my sand-and-clay castle.
Rammed earth structures are generally made from soil that's dug up from the building site, shoveled into frames, and packed down to make walls. They can be built in half the time it'd take to construct an adobe house of similar size and are (I think) more attractive. In addition, they're dry, durable, economical, soundproof, and unaffected by fire and rot ... and because of the heat-harboring potential of their massive walls (usually more than a foot thick), tamped houses lend themselves well to solar applications. (In fact, they're naturally warm in winter and cool in summer.)
Backwards in Time
One of the earliest records of rammed earth construction can be found in the writings of the Roman historian Pliny, who described the turf towers built by Hannibal that stood for 250 years. The Romans, it's said, introduced this form of soil molding to France, where it's referred to as pisé de terre and is still widely used.
In the United States, the construction method reached the height of popularity in the 1940's when conventional building materials were being allocated to the war effort. But as soon as the struggle was over and the economy had recovered, making the more conventional materials once again plentiful and affordable, folks pretty much forgot about pisé.
Chinks in the Wall
Of course, new home builders didn't stop making rammed houses out of sheer fickleness. In truth, these dirt diggings do have some drawbacks, not the least of which is that — even though they don't take as much time to construct as can adobe structures — they do require a lot of hours and a good bit of hard physical labor to build (especially if most of the work is done by hand). For example, in one day you can expect to finish about 70 square feet of wall ... which many would-be earth rammers have decided isn't a heck of a lot of progress to show for the backbreaking effort expended.
The procedure goes something like this: First, you have to prepare the proper soil mixture (about 70% sand to 30% clay by volume. Then, if you like, add enough cement to equal 6% of the total). Next, you'll need to mix just the right amount of water to hold it together so it'll harden properly. And once you've laid down a concrete foundation and made, bought, or rented the cumbersome wooden — or metal — forms that the dirt's to be tamped into, you have to find some way to bully the sand/clay mixture into the molds.
The real time eater (and muscle strainer) is the tamping itself. This can be done with a handmade tool, usually consisting of a long handle (say, a pipe) with a flat piece of metal attached to it. Such a device will have to weigh at least eight pounds to be effective. Once in hand, the tamper is used to pack the earth until it's compressed enough to dry and harden correctly.
This is all fairly basic in theory, but in practice the process can require a good many sweat-filled hours, days, and months of work. Of course, when you consider the money saved, you might decide that the labor and time invested will be well spent. Tamped earth walls are roughly 40% lower in cost per square foot than are those of standard studwall construction.
However, because it takes so long to complete a rammed earth house by hand, the scheduling of the construction is crucial. Climate is of paramount importance in dealing with earthen walls! A single freeze could do a great deal of damage to the drying process, and even change the texture of the earth. So if you live in a region that's hit by frosts in late September, you might want to think twice about starting your structure in August! You should also be wary of rain, since walls-in-progress must be carefully sheltered from wet weather. (Of course, this can be handled by simply covering them with sheets of plastic.)
I first discovered tamped earth houses about 30 years ago when my husband (who was an architect) designed one in Taos, New Mexico for a young artist named Robert Ray. Bob and one helper built the house, under the supervision of his father (an ex-World War II Seabee who'd made rammed earth runways for American bombers in Iran). They did everything by hand except the actual tamping, for which they used a gasoline-powered rammer. To cut other expenses, Bob salvaged some beams from an old barn to make door and window frames. And the cost of his house (not including electrical wiring and kitchen fixtures) came to around $3,000.
Furthermore, Bob's as happy with his home today — 30 years later — as he was the day he moved in. And why shouldn't he be? In all this time it hasn't needed a lick of structural repair!
Well, the Rays' experience convinced me... so, using the New Mexico house as a model (and remembering ideas garnered from other rammed earth buildings I'd managed to visit over the years), I hired an architect, contractor, and crew to have my own earthen dwelling built. All in all, the job took about three months to complete (with the help of an electric tamper), and my spacious 2,700-square-foot home cost me a total of approximately $65,000.
Now that figure may seem a tad high, but keep in mind that I hired folks to do my design work and all my labor, and that I also had to pay for the use of the mechanical tamper. Given sufficient information, however, an enterprising do-it-yourselfer who's willing to devote the necessary time and muscle could do the job much less expensively. After all, soil's free: It's the labor that costs!
Want to Do It Yourself?
One of the best sources of information about rammed earth construction is the Farmer's Bulletin No. 1500, which was put out by the U.S. Department of Agriculture in 1925. Sadly, this pamphlet — like many other publications that deal with this subject — is out of print ... but many public and school libraries do have the Farmer's Bulletin series, as well as some other reports on ramming that you might be able to find by digging into the card catalog.
And recently, a few innovative contractors have begun to develop swifter, more mechanized means of putting up soil shelters, so articles about these earth movers occasionally appear in house design and architectural magazines. Keep an eye out. I have a feeling that tamped earth houses are due for a comeback. Since the dirt beneath our feet is one of our most accessible natural building resources, "packing it in" may well be the best way to beat the high cost of construction.