COMPRESSED EARTH BLOCKS: Interview with Advanced Earthen Construction Technologies’ Lawrence Jetter

Compressed earth block building

Earth. The abundant resource is locally accessible almost everywhere on Earth. The ease of transportation alone makes it a fine green building material, but its benefits are much more than just that. It’s non-toxic, has a high thermal mass, low embodied energy and is disaster-resistant. It’s an ideal green building material, yet it isn’t used much in the West because of the high cost of labour needed to build with it. But with mechanization, suddenly labour costs are no longer the issue they were with handmade adobes. Green Building Canada spoke with Lawrence Jetter, President of Advanced Earthen Construction Technologies (AECT), a Texas-based compressed earth block machine manufacturer, about compressed earth blocks (CEB) and how economically feasible it is to build with them.

What are compressed earth blocks?

Machine-produced adobes. You use them, lay them and do everything you do with traditional adobes, but it’s so much faster and more economical. You can build a bunch of houses in the time it takes to build one house.

What do you think of stabilized earth blocks?

Stabilized compressed earth blocks will have lime, cement or fly-ash in them, making them stronger, but what people don’t realize, according to University of Texas, it takes 20 inches thickness of cement stabilized block to give you the same heating and cooling efficiency you get out of 10 inches of pure dirt. The reason for that is because cement has a crystal growth inside. When it’s curing, it makes a crystal and that crystal becomes a conductor of heat and cold just like a copper wire conducting electricity whereas with lime you don’t have that problem. Plus, lime also does not cure from water the way cement does. Lime cures in co2. If you want to talk about green building, by using lime in your blocks you’re actually scrubbing the air just like a tree would do. You’re consuming co2. A lot of people don’t realize that 60 per cent of the co2 produced in the world today is produced in the manufacture and use of cement. Cement gases off for 17, 18, 20 years. As long as it’s getting harder it’s taking water and turning it to co2 in the crystal growth process.

How do the building costs compare, per sq. ft. if I were to build a standard home with conventional building materials or that same home with compressed earth blocks?

Here in the U.S., if we build a small rectangular home you can do it for about 90 per cent of what it costs to build a brick-and-stick home. But what happens with adobe is that people start thinking about arches and all that kind of stuff. Suddenly their plain little home becomes a custom home. We’ve done homes that were $76 a sq. ft. all the way up to $300 a sq. ft. depending on the amenities they put into their homes.

Now, you can go out and use particle board and siding and build one cheaper than the earth block, but in 10 years it’s going to be a piece of junk. The cost of owning an earth block home is so much less. One homeowner here had a 3000 sq. ft. house with an electrical bill of $320 to $340 a month in the summertime. His new earthen home is 5700 sq. ft. and it’s $100 to $145 in the summertime because earth blocks are so much more efficient.

The block cost varied on one of the houses we built from 49 cents a block to another that was $1.05 a block. That was just the cost of the block itself. It varied that much because of the costs of trucking the soil in. For the 49 cent block we were able to mine the soil off his property. In fact, he used the soil twice. We took the soil and made the blocks with it and then we screened out a rock that was about 1.5 to 2 inches in diameter. He took those rocks, because we had a pretty high percentage of them, and laid them down and put ¾ base on it and then laid his tile on top of that for a road bed.

Why is the earth so much different ?

It’s not the difference here, it’s how they had to truck the soil. Here in San Antonio I took the soil off the property and made the blocks. Up in Austin we had to truck it 30 miles because where he was building there is no dirt. He’s got about an inch of top soil and the rest is rock

In general in the U.S., how much do people pay for soil?

I bought some soil over here that was a waste material for a dollar a yard and they loaded it and it cost me about $100 for an 18-yard dump. I bought waste material. In other words they took the top soil off and sold it to the landscapers. They have 3 to 6 feet of this stuff that’s in the way to keep them from getting to the caliche base that we use for the highways and roadways that they want to sell to the county and the state. Since this stuff was in the way, they loaded it for a dollar a yard—cost—just to get rid of it. But a lot of times you’re going to pay $10, $12, $14 a yard for some of that soil. That’s why I tell people to go to the dirt pit to find a soil that they can’t sell and don’t tell them what you’re going to do with it. That way you can buy it at a pretty reasonable price. You tell them what you’re going to do with it, the price suddenly goes up.

Normally, anywhere in the U.S. we can beat brick and stick by four or five per cent if we stay with conventional building and don’t get into the exotic stuff.

There’s so many benefits and if you can do it for even cheaper, why doesn’t everyone build with earth?

Because no one knows how to do it. I am in the machine manufacturing business, but actually I get into the education business. The architect and engineers don’t know a damn thing about this. They don’t. And it’s not their fault, they weren’t taught. That’s why I’m so happy that the University of Colorado has a machine and they’re teaching it. Texas A&M this year will graduate their tenth or eleventh class. The University of Oklahoma, Dr. Graham also has a machine.

A lot of builders choose to build with earth by hand. How can you compare the costs between handmade adobes given typical labour costs and using your machine?

The soil costs are going to be basically the same because you’ll need approximately the same amount of soil. The difference with handmade adobes is that you need a particular soil. With CEB you can use anything that’s got at least 10 per cent clay in it all the way up to 100 per cent clay. That opens up a wider range of soil, so you can use cheaper soils, which cuts your costs. Building blocks by hand is going to be a lot more labour intensive and slower. You can’t get the number of blocks you need to build a number of structures in a hurry.

Now, if a person’s going to build one house then it’s not cost effective to buy a machine. Because a person is going to build his own house and has years of time, you can’t beat his price.

When you buy adobes in the marketplace, the handmade adobes are not any cheaper than CEB blocks. Sometimes the machine blocks are about 25 per cent cheaper because people can produce more blocks, faster, without all the labour costs.

In some countries the labour costs are not that great, but in the U.S. labour costs would be cost-prohibitive. You couldn’t afford it.

One of the things about traditional blocks is that you need to use thick mud when you lay them. It’s a whole lot harder to lay those blocks because they’re so rough. With machine-produced blocks we can use a thin slurry. You can go from the slab to the barn beam in the first day. If you’re going to build with traditional adobes you can only do three courses and you’ve got to let the mortar cure and you’re going to have some settling because they’re using ¾ to ½-inch mortar. When using this thin slurry, which has the texture of a cheap milkshake, you pour it on, set the block in it and it gets sucked together, creating a monolithic wall, which makes it work a whole lot better in earthquakes. So there’s a lot of factors that enter into this other than the cost of production.

What does an average block sell for in the U.S.?

I hear anywhere from $0.85 to $1.25 depending on the location. If there’s an abundance and no shipping then it goes pretty good. But if there’s an abundance of blocks and it goes a long distance then you’ve got a problem.

How does CEB compare to rammed earth?

There’s a whole lot of resemblance between CEB using thin slurry and rammed earth. I really like rammed earth. I think it’s a great way to build, it’s just so damn expensive. You can do it with CEB for about half of what rammed earth will cost you.


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3 Comments

  • I am in the process of determining how much lime and water to use to mix with the soil from the land I am building upon. The soil is 40-60% clay. The trouble I am having is that of cracking. The more lime I’ve used…the more cracking, but without lime, the clay cracks anyway upon drying. My current plan is to make a lot of smaller bricks of varying percentages of each ingredient and see which one cures the best. Any helpful ideas would be appreciated. Thank You.

  • Any thoughts on how much water to use would be helpful. I realize that I don’t want to be compressing mud (a bit too much water), but too dry doesn’t compress either.

  • Hello Ms Kasper
    I am planning on building with CEB. I attended a workshop a few years ago with Jim Hallock at AECT.

    What machine are you using to compress your blocks?

    I have been digging clay out but have not bought a CEB machine nor anything to mix my soil with water and lime.

    As for your question, I am a novice myself but the experts I have spoken to advise that the water and lime mixture is ultimately determined exactly like you are doing it, trial and error.

    My project is a rather large cottage.

    Thanks,
    Louis
    Fort Worth, TX

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