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Old 11-08-11, 09:37 AM   #1
bennelson
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Default Earth Bricks

Hi Folks,

This past weekend, some friends and I visited the Open Source Ecology project in Missouri.

We were there to tour the place and also lend a hand setting up some earthen bricks. The Open Source brick compressing machine really was pretty cool, and FAST too!

I've got a little video of part of our trip here:


Has anyone worked with earthen brick on a project like a home? It seemed like a great material. We were actually starting to build columns with it. Apparently, they have tested these bricks and they can carry an amazing amount of weight.

Just wondering if anyone has worked with this material before.

-Ben

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Old 11-08-11, 10:14 AM   #2
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Quote:
Originally Posted by bennelson View Post
Just wondering if anyone has worked with this material before?
I knew a house built with a similar material...

Several times, I visited a house that was built in Mississippi, near the edge of the Gulf of Mexico.

The house was built from rammed earth, which is a technique where raw earth, sourced on site, is put into a form, in place, and hand-powered ramming tools are then used to pound "until it rings".

The walls of the house were very thick, almost 18 inches, and provided a very comfortable coolness in the Mississippi summers. The motivation for that type of construction was the extremely low materials cost, though labor was considerably more expensive than 'standard' construction. At the time, because of the war, materials were hard to come by, but there was plenty of labor.

The house was built in the 1940s and survived every major storm, right up until hurricane Katrina... but then every house in that location was also totally destroyed. So, I would say that it held its own.

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Old 11-08-11, 04:40 PM   #3
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Ben, they mention that they used the subsoil, but what was the subsoil. Any idea about the ratios of clay to silt to sand?
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Old 11-08-11, 06:28 PM   #4
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I don't know the exact ratio, but it was very much clay.

The bricks were very hard, dense, and whatever the opposite of crumbly is.

Apparently, they have done pressure testing on them and the bricks can hold a CONSIDERABLE amount of weight.

I did get to see the brick compactor machine run a bit. It's very fast. They have a roller belt on the output end of the thing. The only thing I noticed is that they discarded the first couple of bricks made when the machine started up.

For some reason, right when it starts, not quite the right amount of material gets into the compressor, so it's not squished as hard as it should be.
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Old 11-08-11, 06:44 PM   #5
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Quote:
Originally Posted by bennelson View Post
Has anyone worked with earthen brick on a project like a home? It seemed like a great material. We were actually starting to build columns with it. Apparently, they have tested these bricks and they can carry an amazing amount of weight.
Dumb question time:

- Are these compressed earth blocks (low moisture content) or is the subsoil put in the press wet/muddy like adobe?

- What was the approx. clay / silt / sand ratio of the subsoil?

I have not personally built with adobe (sun-dried, earth and straw bricks) but adobe buildings are common where I live. In the southwest there is a large diurnal temperature swing (day to night temp. difference) and properly designed buildings with good thermal mass can be very comfortable. Adobe is also a cheap material, but labor-intensive to build with. The Wikipedia pages on adobe and compressed earth blocks are pretty informative.

As I understand it the most important issues with adobe are to have a sufficient foundation for the weight of the structure and to keep the bricks/blocks protected from the weather (roof and stucco). Even in the dry Southwest rain and snow can infiltrate a crack in an adobe wall and eventually it will melt away.

FWIW,
Tim
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Old 11-08-11, 07:44 PM   #6
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I don't know the exact mix of clay/silt/sand. It was very clay-like.

The earth is loaded into the top of a big hopper with a bucket loader that has sort of a flail on the front of it. The flail sort of scrapes and flings the dirt into the bucket, and then the operator dumps that into the brick machine hopper.

The earth going into the machine is at whatever moisture content it was at when the operator picked it up ten seconds before.

I believe that they were letting the bricks cure for some amount of time, but I don't think it was long, maybe just a day or two.

In this case the earth bricks are going onto a concrete slab, so they have a solid foundation. When finished, they will be covered with a lime wash.
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Old 11-09-11, 12:55 PM   #7
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How do they handle an earthquake?
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Old 11-10-11, 09:08 AM   #8
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Wow. Those folks are having some fun! I'd urge everyone to go have a look. opensourceecology.org.

I have a lot of clay about 4 feet down, so I'm tempted to try their technique. We have to deal with months of freezing temperatures here in the land of 45 degrees latitude ... and I wonder how long those bricks take to dry out. Neat site though. And nice to see some open source material. More detail would be appreciated (such as soil mix ratios etc) but that might be somewhere in the site I didn't get to. I always get a little twitchy when someone says, Oh they take a lot of weight, but not, good to x lbs per square inch based on a moisture content of y with a materials ratio of b. (not that I'm likely to spend an evening doing all the calculations, it's just nice to know )

TimJ that looks like a great material for your neck of the woods. Adding straw etc might make the bricks a little lighter/stronger too.
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Old 11-10-11, 09:58 AM   #9
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There is an amazing site in Morocco, Ait Benhaddou, which is a fortified city built from compressed earth bricks


That is a stork nest on the right tower.

The walls are about 18 inches thick and spanned with short timbers to make up the roof or second (or third or fourth) story floor. You haven't lived until you have been on the third floor of a mud house. The outside is covered in smoothed mud to protects the bricks and then beautifully tooled. New mud is added as needed--this is not a low maintenance building method.

Compressed earth bricks are still used widely, but the more modern method is to cover the outside with stucco. I saw a lot of buildings where stucco had fallen off. I'd guess this was due to the mud absorbing and then releasing moisture causing it to break away from the stucco. In a dry climate I'd expect to re-do the outside once every 5 years. In a wet climate, I'd guess once every year or every other year.

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Old 11-16-11, 11:25 AM   #10
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Quote:
Originally Posted by creeky View Post
I always get a little twitchy when someone says, Oh they take a lot of weight, but not, good to x lbs per square inch based on a moisture content of ....
When I was on the tour, they did list a specific PSI that they tested the bricks to. I just don't recall the exact number, so I don't want to make something up and spread misinformation.

They had done some pretty scientific testing of the bricks, and they seem to be a very good material to work with.

This one day was my only experience ever working with earth bricks, so I am not an expert, I'm just trying to help share a bit of a neat project someone else is doing.

I definately recommend to anyone interested to visit their web page.
Open Source Ecology

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