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
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!
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.