Coker's Straw Bale Build: September 2020

RAMMED EARTH WALL PART II

So phase II of the rammed earth wall, which is actually the southern kitchen wall in the casita, went into full steam after having the weekend to recover. Ray (head honcho), Jake and Randall started bright and early and Jeff joined them mid morning. The prep work was all done before leaving on Friday so by the time Jeff joined them they had the first couple of layers all tamped down.

First couple of layers complete in the lower section of the wall

Second to last layer of the day poured into the form and awaiting the tampers!

A little tamping action

"Hammer Slammers" in action (Jake's own invention)

If you were like us, you were probably wondering how we would get power outlets and light switches into a solid earth wall. Well we now know how it is done. The outlet and switch boxes are filled with wood and then are attached to the plywood form from the outside. Then the conduit is attached to the boxes and fed out through the frame at the end of the wall. This makes for some challenges when it comes to tamping but you overcome these by using cut to fit wood to do the tamping instead of the the normal 8" and 4" tampers. It is a slower process than normal but it gets the job done. Then once the forms are removed you remove the wood from inside the boxes and "Voila" you have now have power and light switch boxes in your rammed earth wall!

Power outlet and light switch boxes in place

Starting to cover the boxes and conduit

Jeff and Ray doing the final tamping for the day

Just like we did on the concrete stem wall, a key hole slot was dug out of the last layer of the lower part of the wall. This will provide a way for the upper part of the wall to connect to the lower part since we are building the wall over a two day span. The smooth part in the middle of the key hole slot will be the bottom window sill.

Key hole slots and window sill

So you might think that rammed earth is just throwing some dirt (with a little clay in it), sand and Portland cement into a mixing vessel, stirring it around a little and then tamping it once it is in the form. You would be wrong. There is a very specific recipe and Ray has perfected it. Perfected it to the point that he has a small scale that he uses to measure the precise amount of pigment required to get the desired color. In addition the recipe calls for a specific ratio of dirt, sand and cement. We would tell you the ratio but we were sworn to secrecy by Ray.

Precise amounts of pigment and cement

The true art comes when you add the water. There is no exact science. We liken it to making pasta from scratch. First you mix, or in this case, rototill the dry ingredients until they are sufficiently mixed. Then you make a well in the middle of the pile, fill it with water and rototill it again. You keep repeating this process until when you squeeze a handful of the mixture it forms a clump that when dropped from chest high it forms a small peak with a slight scatter pattern. No peak it's too dry. No scatter pattern it's too wet. You need a little of both.

Jeff taking his turn on "Atiller the Hun" during the dry mixing

Wet mixing

Day two started off with not a cloud and the sky and the temperature at about 85 F / 29.4 C and climbing, which was no different from the day before when the highs topped out at 107 F / 41.6 C. We were just hoping this day would at least have a breeze! The first task of the day had Ray putting on his artist hat, he is a very talented artist in real life, and copying his small painting of the wall and it's "clouds," onto the Plexiglass that would be used for the forms on the upper part of the wall.

Ray's artistic rendering of the "clouds"

Ray preparing to sketch out the "clouds" on the Plexiglass

"Clouds" on the big wall

"Clouds" on the small wall

Before we could start tamping, we needed to build the forms for the upper part of the wall. A solid piece of plywood was used for the interior side of the wall and the two Plexiglass pieces were used on the exterior side so that we could use the "clouds" Ray had drawn on them as stencils for the construction of the actual "clouds." Again, this was a very precise process as everything needed to be level, plum and tight so none of the dirt mixture leaked out during the tamping process.

The interior side plywood form is attached

Ray screwing in the small Plexiglas panel.

Jake making sure all the forms are plum and level

And in the middle of all this Jeff had to leave and check on our first load of straw at the local feed store. When he got there they had all 64 bales loaded and were ready to head out on the delivery.

The first load of straw!

Adam the driver hands the bale to Tom and Jeff

Tom and Jeff stacking the bales

Our first 64 bales stacked and awaiting their tarps

Once the bales were off-loaded, stacked and tarped, the loose straw from the off-load was raked up and bagged for future use on the house construction and to ensure the dirt mixture wouldn't be contaminated with bits of stray straw. We want to keep the straw inside it's own walls and not inside the rammed earth wall.

The process of creating the "clouds" takes a very artistic eye. Each layer of the wall starts with about 6 - 8 inches of the loose dirt mixture. This tamps down to about half that height. No problem when you are just tamping one color, but if you are trying to make "clouds" using a different color and make them the same size as the stencil on the Plexiglass, you need an artist's eye. You need spread the lighter colored dirt mixture slightly above and bigger than the stencil so that when it is tamped it comes close to the desired shape. In addition, we wanted to try and have the same "clouds" on both the interior and exterior walls, thus you needed to try and make it even across the entire width of the wall. This was a very tedious and time consuming process.

The artistic process

Jake and Ray doing some tamping

Once the wall is complete a beam will be placed on top of the wall that will connect the wall to the other straw bale walls. The way you connect the wall to the beam is with all thread rods. These rods are plummed and then held in place with baling wire. Then the dirt mixture is added and you tamp around the all thread rods.

Jeff tamping around the all thread rods with the 4" tamper

Jeff creating that art work

The Artist at work

Tamping at the tippy top

The Mad Tampers (Ray, Jake, Randal and Jeff)

The sun sets on two long days of tamping

After the tamping is complete we need to wait two weeks for the concrete to harden to a point where we can remove the forms without damaging the wall. Just like the concrete floors, it will reach peak hardness after about 28 days.

The second load of 65 bales has been delivered

So two weeks later we were ready for the big reveal! We met Ray and Jake out at the property to help them remove the forms.

A sneak peak at the eastern part of the wall

A sneak peak at the western part of the wall

An overall view of the entire build site

We did finally get a couple of monsoon thunderstorms and the desert really responded! Within days the ocotillo had spouted leaves and were lush green, the prickly pear cacti perked up and the barrel and pin cushion cacti put out some blooms.