Coker's Straw Bale Build

RAMMED EARTH WALL PHASE I

Before we get to the wall, we wanted to show you a recent aerial photo of the build site that one of Jeff's friends took while he was out flying, in a private helicopter not the medieval one.

It's starting to look like a house!

As we wait for the slab to thoroughly harden (at least 28 days from pour) so that it can be polished, we are building the kitchen wall for the casita. It will be a rammed earth wall and will be a focus piece in the courtyard. I'm sure a lot of you reading this are scratching your heads and saying "What are the Cokers' up to now ... too much time in the Arizona sun I guess!" Well before you haul us off to the looney bin, let us explain. This building technique utilizes a mixture of dirt (with a certain amount of clay), sand, concrete and water. This mixture is put into a form, rammed or tamped down and then allowed to harden. When the forms are removed you have a solid rammed earth wall. By adding pigment to the concrete and playing with different colored dirt, one can turn the wall into a work of art and that is our plan. Lucky for us, Ray, our architect, is the local master of rammed earth here in Tucson!

The first step in the process is finding all the right ingredients. Ray did some testing on the dirt that was excavated during the prep for the slabs and it passed the test. We are trying to use as many local resources as possible during the build and you can't get much more local than our very own dirt! Plus the wash that runs through our property is filled with what else .... SAND! And we have a well, so all we really need to bring in from off site is some concrete.

The next step was figuring out the color palette. Ray and Jeff started the process by building a couple of test columns. They sifted/screened the dirt from the big pile down by the well solar panels and then mixed in a couple different pigments.

After sifting the dirt, Ray gets ready to start mixing the different color batches

Once we had all the color batches mixed it was time to layer them in the form and start tamping. The process involves putting about a one inch layer of the mix (doesn't have to be all one color) into the form and then you tamp or ram it down. Usually a good hard ten or so tamps will do.

Jeff pouring the dirt into the form

The next step in the process is the tamping.

Jeff getting his workout in for the day!

Jeff taking a break. The mask does double duty, both for COVID and the dust.

This process is repeated multiple times until the form is filled. Once the dirt mixture in the form is sufficiently dried (time is dependent on thickness, height, etc.) the forms are removed and you have a rammed earth structure. Jeff and Ray made two columns, then Nancy and Ray made another column and then Ray made two more columns before we finally got the colors we wanted for our wall.

Jeff and Ray's first column ... too much red for us

Second column is in the form with a colored concrete cap on top

This picture captures the different colors and layers

With the colors picked out, it was time to start on the preparations for the actual wall. One would think it would be a fairly simple process, but you would be wrong. First step was pouring a stem wall which is what the rammed earth wall will sit on. Once that was hard enough a "key hole" was cut in the top, which will help "lock" the rammed earth wall to the stem wall and provide shear strength. Then a box was built around the water pipes for the sink. If we put the water pipes in the wall it would make repairs VERY difficult.

Ray inspecting the stem wall, key hole and water pipe box

Next came the building of the frame for the wall. The wall will be 1 foot wide, 12 feet long and about 7 feet tall. To make building easier the wall is built in phases, thus to begin with only the lower "walls" and the ends are framed. Pipe claps with 2' x 10" boards are attached to the sides so the plywood doesn't bulge out as the earth is tamped.

Rammed earth wall frame

Narrow huh?

Once the the frame was done someone had to climb in and seal the joints with caulking and oil it with vegetable oil so the dirt doesn't stick to the frame when you pull the frame off. Ray drew the short straw and wiggled his way into the frame.

Ray getting ready to do some oiling

Have to get it in all the corners (plywood was oiled before the frame was built)

It's a tight fit!

One other thing we built was a mixing box. This is where we will mix big batches of the dirt, sand, concrete and water. This will be accomplished with a small rototiller. The box is made of sheet metal so we can keep the mix as debris free as possible.

Ray building his custom mixing box

Next comes a lot of sifting. Ray has a cool rig he built that rests on his truck's tailgate which allows you to shovel dirt onto the screen and all the big rocks just roll off the back and the sifted dirt/sand just falls into the bed. We had to sift about four truck loads of dirt and two truck loads of sand. Lucky for us we have plenty of both on the property!