Cob and Glass Bottle Wall at CCAT
From Appropedia
Contents |
[edit] Project Background
The Campus Center for Appropriate Technology (CCAT), a non-profit and demonstration house on the Humboldt State University campus, is currently remodeling their facility. During this process students have been able to gain hands-on experience in the fields of general and “green” construction. Because the bulk of the remodel has been focusing on alternative building strategies, we decided to research and complete a natural building project within the new facility.
[edit] Objective
Our hope was to create and build a beautiful, functional wall in the bottom floor of the CCAT facility. We wanted to employ earthen building techniques within a more traditionally designed home, demonstrating the possibilities for wall materials and technologies. Because of CCAT’s reputation as a demonstration home, it seemed important to us that the house use as many different forms of technology as possible. During this process the students involved in the building will learn about earthen building techniques and practices, and all future CCAT visitors will be educated on earthen construction, and how to integrate it into their homes.
[edit] Criteria
We chose some criteria for how we would measure whether our building project could be considered an appropriate technology.
- Appropriate deconstruction and disposal of existing wall
- Appropriate materials use (local, natural, reused)
- Increased aesthetics
- Affordability
- Functionality
[edit] Design
[edit] Design Considerations
Initially, our plan was to build our cob wall around two wooden columns and a doorway. We were designing a curvilinear wall, which included numerous glass bottle windows, a bench for the gallery room, and shelves on the office side. Because of changes in the interior layout, completed by the construction company, a lot of our initial plan had to be changed.
We were now working with a completed, timber framed wall, with fiberglass insulation, electric, low-voltage, and fire safety wire ran through it, and drywalled. The scope of our project increased immensely, and our final product was going to look very different than originally planned.
Because we were now working around 2x4 studs, we chose to do away with the curvilinear design, realizing that we would have to build in such a way so that all the studs were somewhat exposed. When building with cob, it is important to consider the expansion of certain materials, and how this may affect your cob’s inability to expand and contract. If cob comes into contact with wood, it cannot fully encase the wood, some needs to be exposed to accommodate for woods tendency to expand and contract as environmental moisture levels fluctuate (Lit Review). We designed our wall so that all the studs were visible from the office side of the wall. This also gave us a great anchor for supporting our shelves.
One of our favorite aspects of this wall is the use of the glass bottles to form small windows letting light pass between either room. We wanted to use as many bottles as possible, without effecting structural security of the wall. Per code, we could not put non-tempered glass below 18 inches within our wall (Lit Review, glass code).
[edit] Cost Analysis
[edit] Monetary Costs
[edit] Time Costs
Building a cob wall is a very time consuming process. We had two people do most of the preparations as far as collecting materials and testing. Here is the estimated time spent on the different aspects of this project:
- Planning and Design: Appropriate Tech is a fluid process that requires constant modifications, flexibility and human time and energy.
- Cutting and taping bottles: ~25 hours with two people working. We had to wait for the bottles to thoroughly dry before we could tape them.
- Shoveling and moving sand and clay: ~20 hrs with three people working.
- Mixing and Building: ~6 hours/day x4 days spread over a two week span. We were lucky to have a good volunteer labor force of 15 for the actual construction of the wall and mixing of the cob.
[edit] Maintenance
We would like to see a natural plaster applied to the wall in the near future. A plaster would be easier to maintain than a bare cob wall. The plaster will need to be maintained, but it should enhance the wall's durability in the long run.
[edit] Construction
[edit] Gathering of Materials
We decided to gather the clay and sand first, so that we could begin our test mixes without having lots of other materials and supplies lying around our site, and sitting in the rain! In Arcata, clay that is dug up at most construction sites is trucked off site and then stored in large warehouses. We were able to gain access to one of these warehouses, and had an unlimited supply of free, dry clay for our project. Amped on our progress with the clay, we wanted to jump right into test mixes so we went to the beach to pick up a truckload of sand. While making our test bricks we realized that the mixtures weren’t coming out as planned, for two very important reasons. First off, we weren’t sifting our clay fine enough, so we got a finer sifter and began working with much higher quality clay. Second of all, we were using beach sand, which is too spherical for the clay to adhere to, we were going to need to track down river sand, which is more oblate. A friend had recently mixed cement at his house to pour a new concrete pad and had a couple truckloads of gravel/river sand leftover, so we spent the better half of a sunny afternoon shoveling more sand. This sand was originally purchased at Wes Green’s, in Arcata. We purchased our strawbale, and broke it up before mixing.
Besides clay and sand, our other big-ticket material is glass bottles. All of the glass bottles we used were donated by the ACRC (Arcata Community Recycling Center) and pilfered from friend’s recycling bins. We tried to obtain the most unique and colorful bottles possible, trying to collect everything in pairs, for when it came time for cutting and taping. We washed and stored all of the bottles until we could rent a tile saw.
For constructing the built-in bench and shelves we chose to use urbanite for the bench and salvaged wood for the shelves. Urbanite is broken up concrete, which has been removed from its original site during a deconstruction project. All of our urbanite was donated from various deconstruction projects. When it came time to find shelving materials we scoured reuse and salvage stores, thrift stores, and recycling centers for funky and unique wooden objects (such as old cupboards, shutters, lumber, etc.) that could be sized to fit between our stud bays.
[edit] Bottle cutting and taping
We wanted to add bottles to our wall for aesthetic reasons, and also allow light to flow between the two rooms. To allow for maximum transfer of light we decided to cut our bottles at the neck, and tape the bottoms of like-sized and colored bottles together. We rented a tile saw for 24 hours and cut over one hundred bottles during that time. Afterward, all the bottle halves needed to be thoroughly cleaned and dried so that there was no chance for mold growth after taping. The cut bottles are extremely fragile and “we were afraid to break the really nice bottles. We knew that they were all replaceable, but not without severe liver damage!” The bottom halves were grouped by size and color, and taped together. We decided to mix it up a bit, and add a little pizazz to some of the bottle windows. Small dioramas have been installed using salvaged treasures. Instead of simply recycling the top halves we have decided to try to make chandeliers out of the necks. Stay tuned for future chandelier-making workshops with our leftover bottle necks!
[edit] Deconstruction of existing wall
The downstairs of the newly renovated facility is all new construction. CCAT as an organization had little say in the design and construction of their first floor (being given the second floor for most of their student projects and learning opportunities). Because of this, the interior of the first floor is timber framed, with fiberglass insulation and drywall. Before we could begin constructing our earthen wall, we first needed to deconstruct the existing wall.
When deconstructing the wall we wanted to reuse of dispose of all materials in the most appropriate fashion. The drywall was utilized while it was still installed for testing natural paint batches; a small section was saved to patch a whole that would need to be fixed once the electrical was completed. Once the drywall was removed, the paper backing was stripped and landfilled (unless it can be recycled?), and the gypsum was crumpled up and added to our soil as an implement for clayey soils. The fiberglass insulation was carefully removed and listed it on Craigslist, and FreeCycle, we are currently waiting for someone to pick it up so that it could be used for a small building project. The plastic junction boxes were also removed carefully and donated to a salvage yard, so that they can be reused. All cut Romex (electrical wiring) was too short in length for reuse, so it was recycled at Arcata Scrap and Salvage. The price of copper is on the rise, and salvage yards pay around $.75/pound for Romex recycling.
Although we started this project with a perfectly functional, brand new wall, that required deconstruction and extra energy inputs than necessary, we feel that the exposure of an interior, cob wall within a demonstration home will have a greater ecological impact than keeping the wall that was constructed for us. Not only will hundreds of visitors a year view this wall, but dozens students will have the chance for hands-on earthen building experience. After this project, these students will be able to continue their natural building projects throughout the world, increasing the dissemination of information and knowledge.
[edit] Electrical
When beginning our cob project, I never imagined that I would gain so much electrical experience. Because this wall is in the office, most of the electrical has been run through it, including lighting, low-voltage/data, and fire safety. Per code, electrical must be ran through conduit when building with concrete (Lit Review, conduit code). Because there are few electrical codes in earthen construction, I decided to be safe and follow this concrete rule, because cob and concrete set in a similar fashion. We needed to run all of our wiring in conduit, and electrical, low-voltage, and fire safety must all be run in separate conduit (Lit Review, code), and the conduit routed through separate junction boxes. The conduit, ¾” EMT (steel piping), was run along the studs and up through the dropped ceiling. Since all the wiring had already been run and cut to length, we had to cut the wiring above the ceiling, splice new wiring in, and run the new wiring down the conduit, and finally stub out of the junction boxes. This is all that needed to be done for fire safety, and low-voltage wiring, but the electrical was a little more detailed.
Electrical outlets and switches are “daisy-chained” together, connecting all the junction boxes in series. For our wall, we have a light switch and two outlets that are all daisy-chained together with the rest of the room. In order to keep the room’s electrical all connected we needed to run the light switch up conduit above the ceiling and then run the wiring between the switch and outlets in conduit. The 2x4s needed to be notched out everywhere we ran conduit between the junction boxes, and in order for the junction boxes to attach to the conduit, we needed to switch all of our plastic junction boxes to steel boxes. In order to keep the structural strength of the 2x4s, they cannot be notched (or cut) by more than 40% of their width (Lit Review). To keep all the electrical connected in series we had to run conduit to the connected wall, cut out a section of drywall, attach conduit to this junction box, and run the wire from the cob wall. Now the rest of the wire can run independently through the rest of the room without worry of conduit. This section of drywall needed to be patched (using a portion of salvaged drywall from the deconstruction of our wall).
[edit] Installing the Shelf and Bench
On the west (gallery) side of the wall, we built a bench for people to sit on during meetings and while enjoying themselves. We placed pieces of urbanite on the concrete floor and we stacked more and more pieces of urbanite on top of each other using cob as a mortar in between. We chose urbanite as a material so we could divert it from the waste stream and because of it's ability to hold weight. We chose to cover the urbanite completely with cob for comfort of those sitting on the bench.
On the office side of the wall, we decided that a set of built-in shelves would be more functional than a bench and allow more flexibility in arranging the room to fit a desk and the other necessary supplies. Two shelves were attached to the 2x4 framing before we started building with cob. The cob was blended to the back of the shelves for extra stability.
[edit] Mixing and Building in Sessions
To ensure structural integrity, it is important to build a only couple feet of a cob wall at a time and let it dry for a few days. This is safer than building a giant wet wall that could slump and fall over, causing extra work, energy, time, headaches, sneezing, diarrhea and possible death. Our wall involved 4 sessions of mixing muck, building wall, and building friendships.
- Mixing
We first mixed sifted clay and dry sand, 1:1 on a tarp. We added water until it was a wet, pastey consistency, pulling the tarp corner inwards to help mix. Then we danced around and sprinkled straw (not hay) on top and mushed it in with our feet. We checked for the correct consistency according to the wet tests described below.
- Building
The mix was made into cobs the size of softballs and transported a few yards to the interior of the building: the site of creation.
- Session 1; Day of foundation: We built the bench and the first couple of feet of the wall behind it.
- Session 2; Day of the super volunteers: Our Appropriate Tech class (who we love and appreciate) came to the site to help. We started putting the glass bottles into the structure. It was very efficient and wonderful and full of fun.
- Session 3; Day of almost: We cobbed up to the shelf area and trimmed and perfected the lover levels.
- Session 4; Day of finally: We finished the wall! (except for the touch up work)
- Technique
[edit] Testing
In our earlier mixes, we found that beach sand doesn’t hold together well at all. We then tested different ratios of cob, river sand and clay. While the cobs were still wet, we performed various tests described in “The Cobber’s Companion.”
- Drop Test: We wet the mixes to pie crust consistency and made a sphere 2” in diameter. We then threw it 3’ in the air and caught it on our palm. The good mixes held their shape.
- Crunch Test: We squeezed a ball of clay near our ears. The good mixes had enough sand in them to sound crunchy.
We also performed dry cob tests. These tests are described in “Earth Construction.”
- Compressive Test: We constructed a 1st class lever with the fulcrum at one end of a 2x4 and a bucket at the other end. In between the two was a slice of a dried cob being compressed. We added weights to the bucket to put pressure on the cob and test it’s strength.
- Tensile Test: We put a singe brick on two pipes with another pipe of the same size on top if it. We slowly added weight on top of the upper pipe until the cob broke. This was to see if the cob could hold a good amount of weight.
So far, we have found that our final mixture should have about half as much clay as sand and a medium amount of straw. We have further testing yet to do. These future tests include molding cob around glass bottles, 2x4s and conduit. We also need to test the compatibility of cob on urbanite.
[edit] Conclusion/Discussion
[edit] Introduction
Introduction text goes here.
To make bullets use the asterix:
- Like this
- and two for the next indent
- and back to one...
- Similarly, numbered bullets are like this
- and multi-leveled like this
[edit] This is a level one heading
This is italic text.
[edit] This is a level two heading (etc)
This is bold text.
- This is indented text. Click Show preview, to see what this looks like.
