Back from CalEarth’s 4 Day Earthbag Building Course

Two of my classmates, looking down.

If you’re not familiar with earthbag construction, don’t worry, you’re not alone. Further, when you tell someone you want to build a house out of bags, full of dirt, it’s pretty fair that you’re going to catch some suspicion.

This type of construction goes by several terms which all mean the same thing: superadobe, earthbag, flexible formed rammed earth construction, and even dirtbags if you want to be a little self deprecating. I had been reading about it since 2008 and found the idea fascinating. Over the years I kept reading, kept watching, and had it in my head that I’d give it a go at some point.

CalEarth is the institute that Nadar Khalili created, when he formalized earthbag construction and brought it into the mainstream world of architecture and engineering. It’s been accepted as New Mexico and San Bernardino County, CA building code, and CalEarth has been pushing for full adoption nationwide. In particular, the seismic performance of earthbag domes is literally beyond what the testing machines can provide.

I had been trying to get into CalEarth’s 4 day class since pre-pandemic but like everyone else on the planet my 2020 plans were ruined.

A year and a half later, I managed to get in, and it was definitely worth the wait.

Where to even begin.

CalEarth is in a weird place. I hate to just say an entire town sucks, but you’d be hard pressed to make a case that the trio of Victorville, Adelento, and Hesperia aren’t the buttocks of California. Further, when Nadar Khalili founded CalEarth in 1991 it was a multi-acre plot in the middle of nothing-ness. Later on track housing moved in, surrounding the campus.

CalEarth in the middle and top left, cookie-cutter track housing everywhere else.

When I arrived I met a mixed assortment of fellow students, 20 of us in all. A cattle rancher from east San Diego, a woman who introduced herself as “Prism Shine”, and an architect who was getting tired of building homes “the completely wrong way” as he put it. For various reasons we were all there in the roasting heat of Hesperia, ready to start doing manual labor. And we paid $800 a pop for the opportunity, none the less.

Peep my sick arch, bro.

We learned the value of an arch, a few different types of arches, and where they were strong and how they failed. Not ready to build the Roman aqueducts quite yet, we focused instead on basic principles.

Our little sample dome, getting started.

We spent some time walking around the grounds, seeing previous projects and getting an idea of what this construction model can do. Here’s a good tutorial if I’m doing a bad job of explaining it:

There’s a lot to the construction, but even before that is answering the question of why would anyone be looking for alternate construction? In the USA, we live in wood frame houses. You probably are in one right now. You grew up in one, so did your parents, and you envision your children and your children’s children doing the same thing. Why in the world do we need to change anything? If it’s good enough for everyone you’ve ever known, surely it’s good enough for future generations.

Well, not really.

The style of home we all live in, stick framing, wasn’t invented because it was good. It was invented primarily because it was cheap, quick, and made use of local (in the USA) materials. Stick frame houses tend to be high mainteance, get bulldozed after a few decades (into a landfill), have terrible insulative values, make no use of the earth itself, and as the quality of wood has deteriorated over the years so has the home.

Number of US homes, by age (how old the home is).

The most common age bracket for US homes is 11-30 years, and there is sharp drop after 50 years. And many of us may reluctantly say “Well yes, I don’t want to live in a 50 year old house, I want to live in a new house.” This is largely because of (a) the construction style used (b) using homes as profitable asset and (c) the disposable tendency of our culture. When we don’t like something we discard it and buy a new one and this extends to our homes.

But these disposable homes are very expensive to heat, very expensive to maintain, and loaded with petrochemicals off gassing for years. Your paint, your couch, even the plywood your home is sheathed in: for years they are releasing known carcinogens into the air that you and your family are breathing in. In a hilarious turn of fate, right around the time that most of those chemicals have released, you move into a new house and start the cycle all over again. Your older home eventually gets demolished and pushed into a landfill.

Wood framing also suffers a problem with moisture and mold that almost any adult can relate to. We desperately try to keep the interiors of the walls dry as wet wood means rot and structural failure. Likewise, the interior temperature and humidity is constantly fluctuating. Even just over the course of a single day the humidity can triple and the interior temperature can soar over 30 degrees without any form of supplemental heating or cooling.

In short, we don’t do wood framed houses because it’s a good idea. We do it chiefly because we did it yesterday, lots of people know how to do it, it’s accepted building code, and the materials are widely available. While understandable as to why we got here, it doesn’t explain why we should stay here.

Just as a small example, earthen walls with semi-permeable membrane plasters (like lime) function a bit like goretex. Water can’t go in but vapor can move freely. Even better, the heat energy of the sun is used for the physical process of evapotranspiration. In the same way that water uses the heat of your burner to convert itself to steam, the walls use the sun’s heat to move the interior moisture through the massive earthen walls and out. Lime plaster in particular emits zero VoCs, once applied is non toxic, and is naturally resistant to mold and mildew. Lime plasters do require maintenance: every 5-10 years a coat of lime and water should be rolled or sprayed on to the exterior. That’s it.

Further, wood naturally wants to deteriorate. I see it on the forest floor outside my window. Logs are rotting, sticks are snapping, and the organic detritus goes back into the soil to fuel the next generation of trees. Earth however isn’t going anywhere, certainly not on a timescale that humans can fathom. A jar of dirt from the era of dinosaurs would be exactly the same if opened up now. Even left exposed to the elements, sand and rock change very slowly. Lime plaster is constantly and slowly turning back into limestone, reabsorbing the CO2 that it released when it was heated up in a kiln.

What CalEarth teaches.

The above was a large aside, but it’s hard to talk about earthen construction without first pointing out the shortcomings of the common alternatives.

Four days is not enough time to be good at building homes, that much is clear. But it’s enough to teach the fundamentals, provide hands on experience, and describe where to go from there.

As such we built a (small) dome, but we put a door frame in which is basically the same as a window frame. We plastered, and we did site planning and design. CalEarth was pointedly going over techniques that keep people from screwing themselves up. Using cement stabilized earth as an example: not what I want to do, but it’s hard to say that it’s not a very good way of making sure that if you get a leak your wall doesn’t turn to jelly and fall on your head. They’re happy to have sidebar discussions on other stabilizing techniques, or not using stabilized earth at all, but with only four days they have a curriculum and they stay on point.

The heart of earthbag construction is indeed, earth.

I had never plastered before, the closest I had come was drywall spackle. But this was real no-kidding plaster where you’re filtering the soil, getting the sand, mixing it with a stabilizer, getting the moisture right, and applying. Both in base coats using suction and then in finer detail where you get into pool trowels and sponges. 10 hours isn’t enough to make you an expert, but it certainly gets you moving in the right direction.

Plaster day.

Our final day, and I should note that all of our days were at least 12 hours, was spent on design and construction. How foundations get laid, how to handle utilities like septic and power, and largely how to expand from a structure to a home. What’s good about this is that if you have experience and knowledge with conventional construction much of your knowledge is readily transferable. Even if it’s tackled a slightly different way, a working knowledge of conduit, frost depths, and site drainage plans is very helpful. Earthen construction doesn’t change everything and not every advancement in modern building is a bad thing.

Where to go from here.

When I got my merchant marine master’s license (aka: captain’s license), I needed to have over 300 days of sea time just to apply. From there it was made clear that I was a “paper captain”. The instruction I received and my previous sea time formed the platform that I could now begin to be a captain. It wasn’t an end to training, it was actually the beginning of a new learning process.

There difference between a paper captain and a real captain was experience and there was no short cut: you just need to start doing it. Staying in the safety zone, but pushing outside the comfort zone.

I’ve jar tested nearly every pile of dirt between here and Reno.

So for me I’ve been experimenting with different soils, lime mixes, and seeing what makes a good fill mix vs a good plaster. The next project will probably be building a tool shed dome. Not too big, it gives me a chance to build something not overly mission critical. I can test out my mixes, and develop that hands on skill that you just can’t bypass.

For anyone who’s gotten this far, the other thing CalEarth gives you is a list of ~20 people who possibly are down to come help you with your project because they want to get their skills up as well and better for them to work on your project than theirs. We’re making sure we can accommodate van dwellers and car campers, to make our work site as comfortable as possible for free or nearly free labor. In my wallet I’ve got the names and email addresses of my instructors as well. And while not the free or discounted labor of my classmates, they can answer questions and if I want to bring in the big guns sometimes, I have that out as well.

And lastly, I should note that it’s not like earthen construction is the best in all envionments and we should make wood an illegal product to build with. A good idea in construction is to use the right material and design for the intended use and the environment. As much as any reasonable person can say that wood framing simply cannot be the choice across an entire country, nor could that statement be made for earthen buildings.