Cob Cottage Update

Cob lends itself to massive walls and curved forms. The space it creates feels radically different from what most of us are used to, yet it's so familiar and seems more sheltering. You can't tell from a photo, but the quality of light that passes through a thick wall is also quite different...notice the soft curves and illumination of the window reveals.

On a technicial note, the shelves on the left of the photo hadn't been installed when this picture was taken but you can see the roundwood buried in the wall they will attach to. This methold of attachment was used all over the cottage with the windows, door frame, and roof framing all being anchored by such "deadmen". Also note what the mud daubers left while the building was open and drying for the summer, quite fitting for a mud building!

I traveled back to Chapel Hill in September to help Greg coordinate the finish plaster and pour the earthen floor. We did the interior plaster in one day with a few volunteers, then the floor, and the exterior plaster the next weekend. It was a very busy week and we got a lot accomplished.

Our plaster was a mix of local clay slip (a thick suspension of nearly pure clay in water), sand, and horse manure. The ratios were something like 1:2:1/2 respectively by volume, but don't obsess over numbers. You go by feel more than anything else and your local materials are certainly quite different. An earthen plaster should be very sandy or it will likely crack. It should not feel too sticky but should hold together in your hand. The horse manure was added for tensile strength, as it is pretty much completely fiber.

A properly finished earthen floor is hard and durable, but we decided that a partial brick floor near the door and stove would be appropriate. Aside from functioning as a sort of landing and hearth space the brick added visual and textural interest while complimenting the stone nicely.

 


Our mud hut even has electricity!

 


Pouring the earthen floor.




We mixed our material in a wheelbarrow with a hoe, although for a job of much larger size I would use a mortar mixer. We carried the mix in buckets, spread it on the subfloor and troweled the surface flat. The floor received much subsequent hard troweling as it dried over the next few days.


Greg with the last of the mix.



Once fully dry, after maybe 6 weeks, a treatment of linseed oil and beeswax will serve to harden and waterproof the floor.

Catskill strawbale

Here are some pictures of a more conventional strawbale building, to serve as a contrast to the one at Bonnaroo. I worked as a subcontractor on the bale work in December of last year.


trimmed straw, ready for plaster




trimming the bales flush




A jig for ripping bales with a chainsaw

Piedmont cob

Here are some photos of a cottage I built with my friend Greg in Chapel Hill, North Carolina this spring




The building is set on a south slope for maximum solar gain and it's slightly burmed into the hill, which will help to moderate temperature. We built on a rubble trench which combines drainage and footing functions.




The blank slate. Most of our stones were local igneous bedrock. Others are quartzite and sandstone leftover from building the client's house years ago.




It took a few days to set the first course of stones and the threshold. After that our speed increased dramatically as we went along.






Greg









I played when I needed a break. I learned a whole lot about stone (and these stones in particular) by fooling with them. The foundation benefeted from it.




This was a dry foundation (no mortar!) and I tested every stone to make sure they didn't move



Greg and I taught a couple of cob workshops during the building process. Here we are mixing cob by foot.





Industrial cob alternative




Cob is composed of clayey subsoil, sand, straw and water. It's mixed to a firm yet malleable consistency and walls are built handfull at a time.
















We built the rafters right into the cob walls which made building a curvy roof quite easy. The framing is achored to deadmen (usually pieces of strong forked roundwood) that are buried in cob.










Except for the lumber all the living roof materials were salvaged. Here were are filling the truck with dumpstered goodies.




Green roof workshop








Here you can see the strawbales. The west and north walls are a bale/cob hybrid for greater insulation.




It's not done yet but looking good! We still need to install the woodstove and door, plaster the walls, and pour an earthen floor.

Bonnaroo Post Office

My latest project was at the Bonnaroo music and arts festival in Coffee County Tennessee. It was the 8th year of the summer festival and it was my first experience with such an event. I arrived a week eary to coordinate the restoration of their strawbale post office with a group of volunteers.




Last June a group of volunteers joined the Bonnaroo visiual design team to build a 25'X36' eliptical building with natural and reclaimed materials. Built to be the festival post office, it was designed to evoke the pony express. (cowboy hat)

Strawbales were stacked on a rammed tire foundation, pinned in a cage of bamboo, and parged with an earthen plaster. This load bearing strawbale building was built, roof and all, by mostly volunteers in two weeks. They did a great job as you can see in the above photo from last year.
They built a beautiful example of a resource efficient, cheap as hell building. A whole bunch of people saw it, and even better it's a federal building, a USA Post Office...at least for four days a year.

As a result of the rush before the festival, and with no real intention of the building lasting more than one season anyway, some importat details were missed, most importantly the roof. It was beautifully improvised from scrap lumber and sheets of reclaimed corrugated steel but as is the risk of building complicated roofs, they're much more likely to leak than simple ones.

Upon inspecting the building in May they found that the roof had been leaking above the bales in places. Definetly a bad thing, but otherwise the building was in pretty good shape. The plaster held up well considering it never recieved the final weather resistant coat. Deciding that the building was worth investing in as a permanent structure, a post and beam framework was set under the roof and the leaks were fixed.

I was brought in to assess the water damage to the walls and replace the rotten bales. Then I lead a volunteer crew through the plastering and general fixing-up of the building.

This is the site when I arrived a week before the festival.




The worst of the visible damage looked like this.




There were places where water was sitting at the bottom of the bales as well. Plaster should have come over the tire enough too allow for quick drainage.





Lesson on the importance of detailing. Think like water.




there were other signs that something was wrong...





My first morning I got started right away and busted plaster. With a dust mask and a framing hammer I broke plaster from the worst sections to see what the damage had been. I also dug into parts of the wall that looked good, to see if they were solid, dry, mold free and worth saving. They were.

What I found was that probably 80% of the bales were fine. They were dense, with strong straws and smelled fine. The color of the straw was no longer golden shiny yellow, but a dull dustier color. Where there was water damage it was obvious. The worse places had veins or pockets of black, wet, straw compost. Most of the damaged straw was dry but had been wet frequently enough to be dusty with mold and quite brittle if you pulled on a single or even a chunk of straw.

I took out this entire section. The black vein is compost like and damp. about a 4' section was weak gray straw.




another bad spot




The walls were strapped with bamboo, which helped to keep the oval form. Note the diamond lath bridging the straw/doorframe joint.







the biggest hole




new bales




The strawbale trimming and tying station. Because the walls are curved I shaped the bales in a trapeziod shape to take the curve. As in masonry, the bales are stacked in a running bond with no vertical seams. Half bales are used to stagger the courses at door posts and custom bales are tied with a needle.




After the new bales were placed, I trimmed the walls with a chainsaw to even things up and prepare the walls for plaster. The next step was to apply a coat of thick clay slip to help adhere the plaster to the straw. Then we applied a coat of plaster to the fresh bales, and another coat over the entire building. The plaster was mixed in a mortar mixer. I spent most of my time behind the mixer, stopping every few mixes to check on the progress. The plaster was made of local clayey subsoil, sand, chopped straw, and water. The final plaster mix was made sandier and used finer straw, to minimize cracking and allow for a finer finnish.

We completed the plaster two days before the festival, leaving us a day to paint and build some furniture, as well as clean up and make everything look nice.




nice plaster finnish!




Dusk




Dan working on his beautiful oak and bamboo counter









The building served as the US Post Office - Bonnaroo during the business hours of the day, and for the rest of the festival was used as a place to hangout.