Coker's Straw Bale Build

EARTHEN PLASTERING

Once all the big voids in the walls were filled with cob it was time to start the next big step in the building process ... getting the coat of earthen plaster on the interior and exterior walls. Guru Das and his apprentice Kailee took the lead on this process.

Just like we did with the cob, the first step in the process is to put on a slip coat. With only two people working, three if Jeff was acting as apprentice to the apprentice, the mixing of the slip was done in much smaller batches ... 5 gallon buckets. Since they were only doing one wall at time, they mixed the slip by hand. Kailee quickly taught Jeff the correct technique and the apprentice to the apprentice was put to work.

Making slip the old fashioned way

After Jeff got a little more experience he was allowed to use power tools to make the slip.

Jeff mixing up some slip

Once the slip was applied but before it hardens it needs to be scratched or to use the technical term ... scarified. This ensures the next layer of plaster will have something to which it can adhere. There are several techniques that can be used to do this. One could use the side of a trowel, which is good for hard to reach or small areas. Or you could use a plasterer's scarifier, which looks like a mini metal rake, and is much faster.

Kailee demonstrating the trowel technique

Kailee scarfing the top of the northern house wall

A wall done with the plasterer's scarifier

Once the slip coat was on they could start putting on a coat of the earthen plaster, which is pretty much cob but with less straw. With the mixture being thinner than cob it can be applied using traditional plastering tools such as hawks and trowels. There are myriad methods to mix the plaster but Guru Das used a small watering trough and a drill with a spiral mixing paddle. Once the mixing was complete it would be shoveled into 5-gallon buckets and schlepped to what ever wall was currently being plastered.

Nancy getting in on the mixing action

We have said it many times before but we can't emphasize enough how fun and stress relieving it has been to be able to literally get our hands dirty during this build ... we get to make our dream come true! Taking part in the earthen plastering was just what the doctor ordered. We were both able to get out to the build one day and team up with Guru Das and Kailee on slipping and plastering the eastern exterior wall of the house.

The A-Team!

(A is for apprentice)

Teamwork makes the dream work

One apprentice waiting on another

Jeff working on his hawk and trowel techniques

Jeff applying slip

The process of slipping and plastering was repeated on the exterior and the interior of both the house and casita over the timeline of about six weeks. Our emotions have ebbed and flowed during this building process. When the straw bale walls and roof went up it started to feel like real buildings. As more and more of the straw bales were covered with the earthen plaster it started to feel more like a real house ... albeit a rather messy one!

Guru Das and Kailee working on our bedroom walls

First patch of earthen plaster on our bedroom wall

Last layer of earthen plaster on our bedroom wall

Getting started on the north kitchen wall

Kitchen walls complete

Before we could start on the north wall of the living room we needed to coax some of the straw bales back into alignment. Guru Das had just the tool for the job ... THE HAMMER! He made it out of a piece of glulam beam. No bale could withstand its might!

Alex employing THE HAMMER

(it is as heavy as it looks!)

Guru Das wielding THE HAMMER on the east wall of the house

Guru Das ensuring the plaster is tight up against the box beam on the north wall of the living room

The north wall of the house starts to get plastered

Guru Das on the darby and Kailee troweling on some plaster on the west wall of the house

The finished west wall of the house

(bathroom window on the left and bath tub window on the right)

The finished north side of the house

There are many techniques one can use when plastering. Novices just kind of scoop some plaster off the hawk with the trowel and push it onto the wall (refer to the video of Jeff above). The master plasterers move the plaster around on the hawk and separate out a large hotdog size chunk of plaster and "flip" it onto the trowel. Jeff almost got the technique down but couldn't do it all the time. Guru Das and his crew had it down to a science. But like all things, people come up with new techniques all the time. One of the volunteers Guru Das brought out to help came up with his own technique to quickly and efficiently get the slip on the wall. He just put a big pile of slip on his hawk and then put the bottom of the hawk against the wall and slowly moved the hawk up the wall smearing the slip onto the wall as he went up the wall ... no need for a trowel. The new technique was called the "Fiore Method" after it's inventor.

Cricket demonstrating the technique of a master plasterer

The small window in the living room is one of the special architectural design elements we're really excited about. It has been a challenge to install and will continue to be throughout the plastering process due to the tightness of the space but it will be super cool when it is finished, as it will allow the morning sun to illuminate the north wall of the living room. It also provides an opportunity to show how thick the walls are and shows off the rounded wall corners that are indicative of a straw bale wall.

The small window

A close-up of the cool rounded corners of straw bale construction

Once the final layer of earthen plaster is applied and before it dries a long trowel like tool called a darby is used to ensure the plaster is flat and there aren't any depressions or bulges.

Guru Das using the darby on the casita bathroom wall

Guru Das demonstrating his ninja like darby technique

A nice level finished wall.

Looking from the utility room, through the craft room closet to the powder room. We won't see this view again!

Many people that visit straw bale houses don't believe they are actually built out of straw bales. You can show them the thickness of the walls around the doors and windows but they just can't be convinced. With this in mind most straw bale homes now include a truth wall. A small area of a straw bale wall is left unplastered so that you can see the straw bale. Our truth wall will not only show the straw bale but also the twine used to tie the bales together and a bamboo rod that is used to provide structural integrity in the wall. With our passive house design in mind our truth wall will need to have the ability to be sealed to keep the house air tight, but also open to allow you to touch and smell the bale.

Our roughed out truth wall

The last wall to get the earthen plaster was the east wall of the casita. The southern end of the wall was interesting because we needed to put in some blocking in case we want to mount some cabinets to the wall in the future. Guru Das decided to try out a new technique. Instead of trying to put the blocking behind the bamboo rods, like we did in the house's bathroom and kitchen, he put them on top of the bamboo rods and used short lengths of all thread rods to compress them into the bales. He cut out a slot on the back of blocking for the bamboo rods to sit in.

Casita kitchen wall is prepped for the blocking

Blocking installed

You can see the nuts on the all thread are also inset into the blocking

On the exterior side of the casita kitchen wall, Guru Das used small pieces of wood to hold the all thread nuts. And once the blocking was tightened down with the all thread rods, Guru Das cut the rods with an angle grinder. At first we were concerned that the sparks created by the angle grinder would light the bales on fire, but Guru Das assured us that the straw is packed so tightly in the bales that they are very fire resistant. And at the end of the day he was correct and we are happy to report the casita's east wall did not catch fire.

Guru Das grinding off the ends of the all thread rods

Let the sparks fly!