Building with Dirt (Part 1)

Shortly after Aaron and I got married, we bought a piece of land. Dreams of building our own house morphed into the reality of home construction in early 2008. This is the short version of the story of our home; I hope it will be useful to anyone considering building a more-or-less green home. We made a lot of difficult choices and compromises about materials and designs, and ended up with a very happy hippie home that we adore.

Aaron is a soil scientist, and we knew we’d build our house out of dirt. While there are more high-tech materials out there for energy efficient homes, we never seriously considered anything else. Aaron found a compressed earth block (CEB) machine for sale in Mexico, where it had been used to make hundreds of thousands of blocks for an eco-resort. We bought it, had repairs made by the manufacturer, and then brought “Mariana” home.

Pros of building with dirt: all-natural material, found locally, low embodied energy, excellent thermal mass, fire- and mold-resistant, and easy to build with as an owner-builder. They’re even easier than adobe, because the bricks are extremely uniform and don’t require a thick mortar layer between each course. Cons: not amazingly insulating (R-value of around 0.25/inch for CEBs). Because of the low R-value, additional insulation may be a good idea, depending on your climate. We used 3 inches of spray foam (not a very green building material at all; does that negate the greenness of the rest of the house?)

Bricks coming off the machine at 8 per minute.

Our blocks were made simply of a mixture of native dirt, lime, and water, compressed under very high pressure. The lime is not necessary, but it helps stabilize the bricks against water damage during building. The dirt has to have some clay in it, but the required proportions of clay to sand are fairly forgiving. We had dirt on our property that worked.

Aaron checking out some dirt.

Combining dirt, water, and lime in the mixer.

The downside of adding lime is that another machine is necessary, a mixer, but it may be needed anyways for getting the required moisture well-mixed as well. We were able to rent the mixer.

The blocks for exterior walls are 10” x 14” x 4” (so the walls to our house are 14 inches thick). The press can also make 7” x 14” x 4” blocks for interior walls. We rented a forklift to move pallets of bricks around. I got pretty good at driving the forklift.

Amy driving the rented forklift.

Because we went with lime in the mix, the blocks need time to cure; we wrapped the pallets of fresh bricks in plastic and let them sit for a month. If you don’t add lime, the blocks can be used straight from the press.

Amy and Brendan wrapping bricks in plastic to cure for a month.

Aaron.

Bricks curing.

It took about a week to make an estimated 9,000 blocks. We used about two-thirds of the bricks in the house (we had way less brick breakage than we assumed). The remainder of the blocks have been used for all kinds of walls and sheds and other projects, but a few pallets of slowly decaying bricks are still sitting out there in our “yard,” embarrassingly. Because of the lime stabilization, some of the bricks are still in excellent shape and totally useable after 6 years of being outside and inadequately sheltered!

Beautiful bricks, ready to use.

After making the bricks, it was time to build the house. We didn’t have really any experience in home construction, but we had great friends who helped out, both with labor and expertise. We contracted out for: the concrete slab, the indoor plumbing and solar hot water, electrical, a bit of framing, stucco, and some of the interior wall finish work (drywall and plaster). (The framing in our mostly-block house was only for the upper half-story, a few closets, the roof, and the “wet wall,” the single two-story wall with all the bathroom plumbing; the two bathrooms are stacked on top of each other for this reason. You can run plumbing in block walls by channeling.)

That left for us to do (with help from our friends): the making of the bricks and the mortar, building the CEB walls including window and door bucks, installing the septic system, a bunch of the finishing work (all the tile, wood flooring, installing the stairs and kitchen cabinetry, etc, etc, etc), and acting as the “general contractor” and coordinating subcontractors and pulling permits and dealing with paperwork. Since neither of us quit our day jobs, this felt like plenty on our plates. The home took from April 2008 (making the bricks) to November 2008 for us to get a certificate of occupancy and legally move in. In retrospect, this seems fast, but we’re still not done with all the inside finishing work, six years later (who really needs trim?).

I learned to use Google Sketchup and made a model of the house, which helped us visualize the interior. You can do a person's-eye-view "walk-through" of the house model, which is pretty cool. The house really does look like this!

Google Sketchup model of the house.

To raise the CEB walls, we held an old-fashioned barn-raising party (in this case, a wall-building party) and our amazing friends came out and helped for a weekend.

Friends helping out during the wall-building "party."

Aaron and Steve.

Pouring the mud slip.

Josh is behind Door #1.

Interior walls are 7" thick.

Plastic covering the bricks in case of rain. We built during
the monsoon season.

The mortar between bricks is an easy mud slip made of just dirt and water. The dirt needs to be sifted first with a 1/8” screen to avoid catching small pebbles between the bricks. It's a continual process of sifting more dirt to make more mud slip while building. We made the screen from a piece of old fence and hardware cloth.

Sifting the dirt for the mud slip between bricks.

After about two weeks to build the CEB walls, not including the time to make and cure the bricks, our contractor knocked out the framing in, like, two days.

Roof and upstairs framing.

Inside the garage, which houses our
little climbing wall. 

In another post I’ll talk about the energy-efficiency and water-saving systems in our house and discuss how they have performed over the years, and perhaps another one will show off the hard work we did to finish off the place and make it look presentable.