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The Clay/Straw Greenhouse

NATURAL BUILDING:  How to build with clay/straw

Building with clay/straw is called natural building. It’s called natural when the parts can return to the earth after use without much, if any, impact on the environment. It is different than Green Building, which uses all the latest technology to build a structure.

First you have to find the clay.

Luckily we had a friend who was a potter and he pointed us in the direction of Healy. Upon arrival we found his spot overrun with big backhoes and gravel trucks. They were building a new road. Unfortunately they had scraped all of the clay off and trucked it off to the dump. Turns out clay is the bane of many a construction worker’s existence.

We managed to scrape up a sample to take home with us and test.

Turns out it was very pure clay.

To test clay….

The first test:

You pick up a chunk and add water. Hopefully if you are in the field you will have a bottle of water with you. You work it and work it until all the lumps are out of it. You roll a snake between your hands until it is about 1 finger thick. Turn that snake into a complete 360 degree circle. If it does not crack, this clay has passed the first test.

The second test:

Reshape the snake into a round ball. Hold it above pavement, a flat stone, or your field notebook. Drop it from about shoulder height. If it goes SPLAT, makes a flat bottom, but doesn’t fall apart, your clay has passed the second test.

The third test:

Sorry, I can’t remember the third test. We’ve never gotten that far in the field. Usually the samples pass or fail the first test and then if it passes, it’s always passed (so far) the second test. If it fails the first test, we continue looking.

Once you’ve found a good source

You start shoveling.  We’ve found that if the clay is wet when you are shoveling, it’s really, really heavy, but it dissolves in water much easier when making slip.  If you find really dry stuff, it is almost easier to powder it before you add it to water.

We carry ours in big rubbermaid tubs.  We tried using the trash can with wheels, but alas, the wheels broke right off.

Make sure you have a heavy duty vehicle.  I wouldn’t want you to ruin your transmission trying to haul too much of this stuff.

Once you’ve found your spot, don’t tell anyone. It’s like a secret fishing hole. You just don’t give it up. Well, I suppose you could trade the location for some rhubarb pie!

Making clay slip

Fill a 30-50 gallon garbage can about 1/4 full with clay. Add water and mix. Note: You need a special super power drill and a paint paddle. There will be chuncks, so leave it over night or even longer. Run the mixer any time you walk by and slowly the lumps will disappear.

Hint 1:  only use BRUTE brand garbage cans. We learned it the hard way.

We had a class of 12 students working on building the rocket stove this summer. Suddenly the doctor, who was a tiny little lady, started asking what it should feel like when she is mixing with that big drill. No sooner had she asked when the whole side of the garbage can blew out and that slippery clay mixture went everywhere! It was crazy seeing all of us scrambling to try to scrape the clay off the garage floor. Anyway, use BRUTE. They have much thicker sides. It will save you much trouble!

Hint 2: Don’t lift the mixer out of the clay while mixing!

   Unless you want to get splattered in clay.

Hint 3: Decide what thickness of slip you need.

Slip #1

Stick your finger in the slip. If the clay covers your fingerprints and you can see the outline of your fingernail, you have a number one slip. It has the consistency of milk. Number one slip is used to coat perlite for the foundation/water proofing. according to Lasse Holmes, Alaska’s only professional natural builder.

Slip #2

Stick your finger in the slip. If the clay covers your fingernail, but you can still see the outline of it, you have a number two slip. It has the consistency of cream. Number two slip is used to cover the straw. says Holmes.

Slip #3

Stick your finger in the slip. If you can’t see your fingernail at all, you have a number three slip. It has the consistency of a milkshake. You can run your finger through it and the track will slowly fill in. Number three slip is used to make plaster to cover the straw/clay walls. Holmes continues.

Slip #4

Sometimes you need a number 4 to mix mortar for a clay bench. That’s as thick as you can get it. says Holmes.

So you want to learn how?

First of all, there are occasional workshops at the AEPC.

If you want to find out more, you can contact Cindee at alaskanbioshelter@gmail.com for dates and times.

Secondly, you could read The Hand-Sculpted House: A Practical and Philosophical Guide to Building a Cob Cottage: The Real Goods Solar Living Book by Ianto Evans.

On Amazon it WAS $35.00, but is now only $24.96.

If clay/straw is not for you, there are other types of natural building

  • Log
    • used a lot below the arctic circle in Alaska
  • Sod
    • used a lot above the arctic circle in Alaska
  • Straw Bale
    • tends to mold, or catch fire
  • Rock
    • is pretty cold
  • Earth-sheltered
    • you only have to heat from the ground temp (in SC Alaska it’s 38 degrees) up, even if it’s -20 outside.


    Recipe for Clay/Straw Walls

    Building with Clay/Straw is so environmentally friendly and natural.
    Here is the recipe that I used for the greenhouse walls at the bioshelter.
    *Note this is the insulation between 12 inch timber frame walls.


    • 1 bale of straw from Palmer
    • 4-5 five gallon buckets of #3 clay slip


    1. Spread about 1/4 of the bale on a slab of cement, taking care to separate the pieces.
    2. Drizzle one bucket of clay slip over the top of the straw.
    3. Using 3 man-powered pitch-forks, toss the straw as if you were tossing a green salad with salad dressing.
    4. When the straw begins to get heavy and the tossers tired, take a break and check the saturation.
    5. Pick up a handfull of straw covered clay and twist it in opposite directions.
      If moisture beads up, it is ready to go. If it doesn’t, there is a need for more clay.
    6. Continue process until the straw is moist enough.
    7. Clay can sit over night in a trash can and get a little sticky, or you can use it immediately to stuff into the walls.
    8. *Make sure the lathe comes up from the bottom between the 2x4s. Stuff walls tightly, but not too tight. Add more lathe as you go.

    This recipe varies by day depending on the humidity, the temperature and the time of year,
    so practice with some models before you build the final product.


For any other of Cindee’s web sites, you can go to:


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