Tuesday, January 27, 2009

Rammed Earth Chicken Coop In Austin, Texas

I came across this rammed earth chicken coop while flickr-ing around last fall and asked the rocking Mr. Cliff White to share his construction experiences with fellow rammed earth enthusiasts.

Where is this project?
This chicken coop is located at my son's school. Part of their curriculum is gardening; I offered to build one to allow them to keep 24 chickens.

Why was rammed earth used?
I've built a shed and a retaining wall; this gave me an opportunity to refine my skills in rammed earth. That said, rammed earth is durable, cheap and beautiful. It's very forgiving and practically anyone can build with it. In keeping with the vision of the school, it was a natural choice.

How thick are the walls and what size is the structure?
It's 9 ft x 15 ft. The walls are the same width as concrete block: just over 7.5 inches. This is extremely thin I know but since I was not so much concerned with the thermal flywheel effect as being inexpensive and quick (less material and less time ramming more material). I used concrete block in an effort to quickly build a stem wall and that was the width of the block. My utility shed in my backyard has stood for about 3 years with no problems using the same width.There is no reinforcement in the walls.

How did you attach your doors and windows?
The windows were built in place - I don't recommend it. Sure for a chicken coop it's fine but they were not square. I used scrap wood to make a volume displacement box (as described in Easton's book) but instead of removing them, I simply left them in place (I put screws through the boards before ramming to make sure they were secure). Using these 'gringo blocks' - in Adobe parlance - I attached 1/4 inch hardware cloth and nicer trim wood to make "windows". This serves a dual purpose: allow the kids to view the chickens when they are not in the yard and, more importantly, air out the coop!
The door was built from scrap 2x4 lumber culled from disassembling the forms and walers.
I attached hardware cloth to the frame and voila! The door! The door jamb was made from (somewhat warped by then) wider walers attached to the rammed earth wall using concrete screws. I had to use many of these to provide enough friction to secure it.

What was your forming system?
One corner form made from plywood, 2 x 6 and 2 x 4.
One straight form from the same materials.
I used 3/4 inch black iron pipes and pipe clamps.
The corner form, straight form, pipes and clamps were like the ones described in David Easton's "The Rammed Earth House

How did you finish the top of the walls and attach your roof?
I poured a bond beam -not very well I must admit. Like I said above, rammed earth is forgiving. More so than I am! I used metal angle brackets and concrete anchors to secure the wooden roof to the bond beam.

What type of equipment did you use?
I used a 4in x4in x about 3' piece of lumber attached to a 3 ft long 1 inch diameter steel pipe. For corners, I tamped with 2x4s or whatever was available and many work gloves. I used a concrete mixer to mix the cement, dirt, and water. Five gallon buckets were used to lift dirt into the forms.
Since I was trying to do it on the cheap, I did not rent a backfill tamper and air compressor. The tools would have cost greater than $100 a day. I believe it cost much more in time; if I did it over, I'd spend the money on lumber to create a single form encompassing the project and rent the power tools!

How did you come up with your mix?
A few years ago when I was making adobe, I tried out different mixtures here at my house. I found the nearest quarry has at least two mixes that work. I performed 'field tests' suitable for adobe blocks and the data gathered from my 3 years standing structures in my yard.
So now, I can simply have the dirt delivered if I doubt the integrity of on site dirt.
I admit that this was the most daunting task for all my rammed earth endeavors. I had no experience with knowing how good was 'good enough'. I was very cautious at that stage; once one works enough with soil mixtures one gains confidence. For instance, I can tell if a mix has too much silt by the sound it makes when I rap my knuckles on a test block! That took a lot of knuckle rapping and drop tests though!

How long did it take to build the walls?
I found I could mix, and tamp about 6 hours a day (on the weekend). I believe - and it's at least reasonably close - it took 20 minutes to collect and mix, and 20 minutes to tamp 3 five gallon buckets. On occasions when my wife mixed for me, it cut time in half and allowed me to labor longer.

I work full-time and was playing in two bands, so my time was limited to weekends and a vacation. Some injuries and inclement weather pushed this project to two years! My wife estimates 160 hours with 60% of that time was me working solo.

Knowing what I know now I'd:
1) Build a single monolithic form - or cost prohibiting - as large as possible. Forget modular as much as possible. My time and enthusiasm are more valuable!
2) Use tamper and compressor and at least one concrete mixer
3) Take two weeks off from work to prepare foundation and build the form and have dirt delivered.
4) Use a whole day on the weekend (not the whole weekend!)

I believe after the the form was up and secure, actual mixing and tamping using just my wife and me could be done in four days - four saturdays. But I haven't used the tamper so it's a guess.


Catarina said...

nice work here!
i would like to ask you a question: do you have idea how many earth (like in kg or something) have you used to build that?!

thank you in advance!

Rammed Earth said...

I'm guessing about a ton per wall.

Larry K said...

I live in Austin, Tx and very interested in the building technique, I have questions and would like to see your completed projects if possible, what yard did you get your sand from.....thanks, Larry K

Rammed Earth said...

Larry K,

Send me your email address and I will pass it along to the man in Austin who built this coop.

Kathy REi4E

R and E said...

Sounds like a "fun" project. You talk about trying out your mix but never give ratios. What is the ratio of cement, dirt, and water that you have found best? What do you do to handle waterproofing?


Ultra Thin Ghost said...

R and E,
This is Cliff, the builder of the chicken coop.
I intentionally left out that information because the ratio will change depending on the soil. Having said that, I used %6.25 by volume of cement. That was a convenient percentage because my tests were strong enough AND (probably more importantly :) ) I was able to use a protein powder container. One container full of cement to one 5 gallon bucket of dirt came out to be %6.25. This amount of cement is enough to waterproof as well. I have a retaining wall I made with the same materials unmarred by 3 years of weather.

Here is a video of my soil tests for my first rammed earth project: a shed in my back yard. It gives much more detailed soil information.

Teckton said...

did you say you used 6.25 percent? cement .Five gallons of dirt to how many pints of cement. What kind of cement did you use. what was the amount of water used in the ratio given?

Ultra Thin Ghost said...

This is Cliff the builder of the chicken coop.
I used %6.25 by volume of cement. David Easton (The Rammed Earth House author) typically uses %7. The soil here in Texas does not require that much. In fact, I could have gotten away with less. It was a quick way to measure cement.

Take your convenient container of choice and a five-gallon bucket. Use your container of choice (mine was a protein powder canister), and count how many containers of soil it takes to fill up your bucket.

Compute the percentage your container of choice is to the full bucket ( my first try with an orange 'Homer' bucket from Home Depot took 20 protein powder containers full to fill the bucket). Try for %5-%7 as a starting point. Since 1 container for me (the first time) was 1/20th of the full bucket, that yielded %5. My next container was a different brand and yielded %6.25. That's why I said %6.25.

The amount of water varies: you'll want to start with a dryish mix. Try squeezing it in your hand and dropping it from hip high. It should break apart mostly. This is a good starting point. Remember, you are merely getting enough water in to lubricate the particles of soil (and activate the cement). The soil should NOT stick to the tamper. If it does - add a bit of cement to suck up that water.

Cement was Type II portland. On my shed in my back yard, I alternated white and gray color. For the chicken coop I stayed with the much cheaper gray.

I can't stress how important it is to just start doing it. Hands on is a great tutor. Make some adobe sized bricks. Leave out in the weather for a week and see how strong it is.

My first hands on was using my adobe forms to make rammed earth bricks.

Hope this helps - I'll try to get my other video footage up since it seems to be generating interest.


CT said...

The builder mentioned having built a rammed earth retaining wall. Do any special additives or treatments have to be used with rammed earth walls in direct soil contact? What kind of footing did he use?

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