Cob Workshop, October 2011; Lessons Learned
Posted by ataraktos on
2011-11-06
October 2011, we attended our first cob workshop, held by Disputanta Cob and Diane Jennings. We met looks of awesome people, learned a lot about cob, got very dirty (which is pretty much the main point!) and ate very well! (We were a little concerned about starving, to be honest but I think I may've actually gained a pound or two that week!)
Anyway, the first thing we did, on the drive back, was jot down a bunch of thoughts and lessoned learned from the workshop - hopefully, one day, we'll apply these to our own cob buildings so I wanted to type them up here, so I wouldn't lose them.
- No burnishing.
- The only activity of the workshop that I particularly disliked was the burnishing of the inside plaster. Burnishing was rubbing the plaster with a piece of hard plastic, to bring out the clay and give the plaster a shine. Think of it as hand-polishing all your walls. Some alternatives may be to apply a lime plaster/paint on the inside or apply a plaster that's very high in clay content. Perhaps there may be some way to speed up the burnishing with a buffering attachment on a drill? I'm thinking, though, that lime plaster on the inside would be the best way to get around this to-me-unpleasant task.
- Earthen Floors might not be durable enough.
- We had the opportunity to watch some earthen floor being installed. It was a gorgeous red color from some local potter's clay ... a few other workshop participants were familiar with earthen floors, though, and said furniture (like kitchen chairs) could easily damage earthen floors. While I would like the thermal mass of all that earth in earthen floors, I don't think I'm willing to deal with needing to be so careful with legged furniture. We would like to use radiant heating in our floor, though and poured earth would be perfect for that. Perhaps poured earth would be a good sub-floor with tile overlay? I would also be happy with urbanite flooring, at least in parts of the house, but I can't figure out how to use radiant floor heating with thick urbanite.
- Connecting dis-similar materials.
- We are considering building parts of our house from urbanite - the bathroom, for instance. I'm not convinced that a cob bathroom could easily handle all the moisture from a regularly-used shower and tub. We were wondering about how to attach a cob wall to a vertical urbanite wall (not a foundation - that's easy - set a few tons of cob on top of your urbanite, and you're done!). The potential problem with attaching cob to a stone wall is that the cob will shrink and settle, while the stone/urbanite wall will not budge. Diane said you'd use a technique similar to using dead-men for installing a door - you can drill into the urbanite and leave "stuff" sticking out, horizontally, of the urbanite/stone section. The more I think about this approach, I think I would also cob in some sticks on the cob side and leave a gap - maybe 6 inches between the two walls. After the cob settled, in-fill the gap. At least, with this approach, if the cob cracked during drying, it should just be the in-fill section, and not my entire wall. Plaster should take care of any small cracks.
- Frame windows and doors
- Another thing we learned - it would be a good idea to frame all windows and doors before installing. Install and cob around the frames, and only after cobbing was complete (but before plastering), re-set the windows in their frames.
- A few advantages - you'll already have a frame in place, should you ever need to replace a window. You won't risk breaking your windows during construction. You'll be able to hand things to each other through your window openings. A carpenter also suggested you can frame fixed windows with a frame and stops for the glass. Cob up the frame and one stop.
- For doors, cob up horizontal tree limbs or boards. These can be cut off, flush for a door frame to be installed and gaps can be filled in. This would avoid any issues with settling cob deforming an already-in-place door frame.
- For working window frames, I may "double frame" the bottom, to leave sufficient room for cob and plaster and to still be able to reach the working part of the window.
- You can't have too many dead-men!
- It would probably be a good idea, especially in places like the kitchen, to bury continuous "dead-mean" at certain heights, to hang cabinets and help attach counter-tops. Anything you want to hang needs a dead-man, so you really can't have too many.
- High stem walls
- We decided at the workshop, we want particularly high stem walls. A few reasons (besides the obvious of floods and mud houses don't mix well)- they build faster than cob. High walls will give enough "pattern" to your stem wall to make it more attractive. One concern about "more rock" is that it's more surface to mold due to condensation. I'm not sure if this would be a problem but I feel confident that some application of mold-retarding-something could be applied a couple of times a year and this wouldn't be a problem. If nothing else, lime plaster could be applied to the foundation, too.
- Seating / floor height
- Ramps are good.
- If our final dwelling will have steps, put in temporary ramps during construction. Stepping up and over a 2-foot-wide-threshold gets old. And is dangerous.
- Plywood and snow shovels
- Cover inside pre-floor not only with tarps but top with plywood and clean up cob shavings with a snow shovel. Cob gets really heavy, really fast. Dragging heavy tarps of it sucks. Shovelling into a wheelbarrow and rolling it out (on those temporary ramps) seems like a better plan.
- Cobbing up to a roof is hard.
- We helped finish the walls on one building, which had its permanent roof in place. I like the idea of having a good roof in place, to help with rain and protect green walls. But cobbing up the the rafters was really hard (or it looked really hard - Carey did a lot of that work!) Although I don't have any concrete ideas about implementations - I'd like to either have a temporary roof, that could over-winter, if needed or be able to lower the permanent roof to meet the walls.
- Plaster Tips and Ideas
- Wet cellulose before adding to plaster mix.
- Add soap to lime plaster for shine.
- Add mica to plaster for glitter.
- Try high clay content/low sand for internal plaster.
- Wheat paste can be used as a milk substitute in plaster.
- Cattail fiber can be used in place of cellulose
- Wiring
- Even though cob is pretty much fire-proof, we've decided that we want all electrical wiring in a conduit. This would have the added side-benefit of forcing us to plan our wiring and cob up with the conduit in place.
- Plumbing
- We've been a little worried about plumbing and leaks. The older house we rent has had several leaks in the walls. If the walls had been made of mud, and also load-bearing, this could be a disaster. One workshop participant had the brilliant idea of using "Pex" tubing, encased in PVC (thanks, Tom)! This way, in the case of a leak, you could just pull the pex tubing out, and thread a new piece in. We've since found a product called Bendit that heats PVC so that you can mold and bend it - perfect for rounded, cob walls!
- Floor Drainage
- We also had some ideas for the rock/gravel sub-floor, especially if we top that with earthen floor and anything poured and wet. To keep the rock unclogged and able to provide drainage, we might cover with newspaper or some coconut mat that was mentioned as used in septic tank installations, for keeping drain pipes clear.
- Roof Design
- A good, single slope roof should be fine, for covering an irregular shaped building. Check the recommended pitch (for snow) with the local extension office or building code enforcement office. While good overhang is important to shield against rain, too much overhang will shade your walls in the winter.
- Insulation
- I don't have many good ideas for inside ceiling materials. I want something that "matches" and looks "right" with cob walls ... I'm thinking about whole, cut bamboo? Should be long enough to span easily. And hopefully, strong enough to hold up 12-18 inches of cellulose fiber insulation? Anyway, cellulose is a good, light-weight insulator. And it's also not wool and vegan.
- Tapered, rounded walls
- Although more work, we think tapered-towards-the-top and rounded walls would be stronger. And for the added work of leveling tapered walls, there's the upside of applying less cob for the taper.
- Plan ...
- I don't have much of one at the moment, but it seems like you need a good plan for where your walls meet your roof. This is related to my earlier roof bullets.
- Laser Level
- One of the more difficult tasks we watched was re-digging out the floor and preparing to pour the earthen floor. This would have been easier if so much cob hadn't fallen such that re-digging was needed. And with the incorporation of a laser level (and a little tripod, if it's not possible or economically feasible to buy one that levels in all directions at once.) Evin has also read about obtaining similar functionality from a bucket of water and a long piece of tubing. It's a little complicated for me to even want to type it up, though.
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Another useful thing will be to keep future floor height in mind, when building window seats or built-in furniture. Maybe construct a box about as high as your floor will be and use it as a foot stool, to test furniture height.