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CCAT greenshed cordwood wall
- 1 Project Background
- 2 Project Members
- 3 Project Definition
- 4 Literature review
- 5 So what is cordwood?
- 6 Mortar Testing
- 7 Criteria
- 8 Materials and Retail Costs
- 9 Tools to be barrowed from CCAT
- 10 Proposed Time Line
- 11 Some lessons learned
- 12 Updates October 2013
- 13 Appropriateness
CCAT is building a tool shed with green methods in mind so it is called the green shed. Part of this green design is the walls that will be made from as many natural or recycled materials as is reasonable. This project offers students the opportunity to get hands-on experience with various wall infill methods and materials.
The concrete foundation of the green shed was poured to make a standard 6 inch wide wall. This is not wide enough for most earth building methods to be of much insulation value. The foundation for the walls will have to be widened to accommodate.
The frequently wet nature of our climate may present other obstacles. The water soluble nature of many natural materials will be considered in material selection. Some methods using organic matter present the issue of rotting. The tendency of organic matter to rot in out wet climate will require the walls to "breathe" well so as to not trap moisture inside.
An existing example of natural wall construction exists at CCAT, CCAT natural wall construction is an example of papercrete and of straw and clay-slip. It may yet be used for inspiration on the insulation walls. Cob and cordwood are also being considered.
Garrett Duffy and Marqes Mayo
The north wall will be another example and experiment in natural building. Insulation will be one functonal motive but also keeping in mind that this wall is for a tool shed. This wall will be designed to hang tools on in some way. The natural bulding technique known as cordwood fits the demand for insulation and offers future builder the opportunity to mount hooks for tools.
- Callahan, Tim, and Clarke Snell. Building Green: A Complete How-To Guide to Alternative Building Methods Earth Plaster * Straw Bale * Cordwood * Cob * Living Roofs. New York: Lark Books, 2005. Print.
- This book offers a fairly solid overview of the listed building methods. For cordwood it warns against various errors the experts have made, such as using hardwoods and sealing the wood ends.
- Chiras, Daniel D.. The Natural House: A Complete Guide to Healthy, Energy-Efficient, Environmental Homes. White River Junction: Chelsea Green, 2000. Print.
- "The natural house" goes into more detail about actual construction and foundation considerations.
- Cordwood Building: The State of the Art (Natural Building Series). Gabriola Island, BC: New Society Publishers, 2003. Print.
- This book is by far the most comprehensive book found so far and is exclusively about cordwood construction. It details mortar mixtures, wood types, wall types and some advanced methods.
- Callihan, Tim and clarke snell. Building green new ed. A complete how to guide to alternative building methods Earth Plaster*straw bale*cordwood*cob*living roofs. N.Y.:lark books2006 print
- this book lays out a nice summary of all these types of building methods along with the mistakes that even the best have made. Morter tests. types of wood more suitable for the construction and so forth.
- Roy L. Robert. Earth sheltered houses; How to build an affordable underground home. 2006 print
- this book offeres info on all the aspects of cord wood. it was here where i found out about foundation and what to do to ensure that your building is level.
- Cory F. Erick. Green building and remodeling for dummies. 2008 print
- This book offers a real simplistic look at cord wood and the properties that it carries. This book talked about how labor intensive it is and recomended a group effort.
- Pierquet, Patrick , Jim Bowyer, and Pat Huelman. "Thermal performance and embodied energy of cold climate wall system." Forest Products Journal 48.6 (1998): 53. ProQuest. Web. 13 Feb. 2010.
- The concern of this article is the thermal performance of twelve building methods and their embodied energy. Two of methods of relevance to this project are 2x4 construction and cordwood for the sake of comparison.
- Jacobus, Frank and Brickford, Keith. "Carbon-Nuetral McCall:Developing a zero energy campus in McCall, Idaho. Day creek journal. june 2009.web. 5 april 2010
this journal mentioned some r-values and expeiereance with rammed earth and cord wood construction. i learned a little bit more about the thermal insulative qualities of this technology.
- Stankevitz, Alan. "DayCreek Journal - June 25, 2000." Daycreek Home Page. N.p., n.d. Web. 13 Feb. 2010. <http://daycreek.com/dc/HTML/journal062500.htm>
- The above site has a responsive forum for those who have cordwood questions.
- "Cordwood." Chaetreuse. N.p., n.d. Web. 13 Feb. 2010. www.brightgreenresearch.org/images/pdf/2009.11.02_MaterialConcept_Cordwood.pdf
- This page reports some information about cordwood, such as R values and compressive strength of mortar mixes.
- Stankevitz, Alan. "DayCreek Journal - June 25, 2000." Daycreek Home Page. N.p., n.d. Web. 13 Feb. 2010. <http://daycreek.com/dc/HTML/journal062500.htm>this is the same source that garret used. i found the fourm questions to be helpful if you have questions.
So what is cordwood?
Cordwood is among the several common natural building methods. Firewood is often sold in a unit known as a cord. Such woods are at times a suitable building material. The more rot resistant softwoods tend to be best, such as white pine, cedar, spruce and juniper among many others. Logs that are at least 12" long are secured in to the wall with a mortar of sorts. The lengths of the logs are mounted perpendicular to the wall itself. The mortar may be made with concrete, cob, or even papercrete. The plan of this project is to use western red cedar logs and mortar made from Portland cement, sand, lime and wet saw dust.
The stability of the mortar is very important. Shrinkage of the wood or the mortar is to be avoided. The mix suggested by cordwood expert Rob Roy, author of "Cordwood building: State of the Art," has the strange ingredient of wet saw dust. It acts to slow the drying of the mortar. This helps to prevent cracks and gaps between the logs and the mortar.
As mentioned above soaked saw dust is mixed into the mortar to slow the drying process. Also not all sawdust is the same. Some of our tests include sawdust passed through a 1/2 inch screen and other through a 1/4 inch screen. The concern is that if the saw dust is to large it may make a crumbly mortar and if it is too small it will not store enough moisture. Hardwood saw dust should be avoided as it makes a crumbly and difficult to work mortar. (Roy 28)
Thin planer shavings passed through a half inch screen as well as chainsaw dust worked the best. We had no problems with mortar cracking in any of our test samples, including the control which didn't have any sawdust. However we only did one test sample for each sample of saw dust. Even though our control sample with ut any sawdust did not crack we would not conclude that saw dust is not necessary from this test alone.
Shavings that were too long produced a mortar that is hard to smooth down. Passing shavings through a half inch screen (hardware cloth) solves this problem.
Very course "saw dust" from a particle board mill produced a very crumbly mortar that broke much more easily than the other samples.
Very fine sawdust made a weak spongy mortar.
Chunky pieces of wood that passed though a 1/2" screen can be removed by soaking the saw dust in a bucket for a few hours with lots of excess water. The thick pieces will float to the top when the sawdust in stired up. They can be removed by hand.
|Maintainability||Repairs expected less than once per year.||8|
|Long lasting||At least 8 years expected||7|
|Appropriateness for tool shed||Can accept at least one shelf||4|
|Tolerance to wet climate||Not expected to mold or rot||9|
|Ease of getting materials||Most materials acquired in Humboldt bay region||8|
|Ease of building||Done with unskilled labor||7|
|Thickness||Less than 12 inches||10|
|Insulation||R-value comparable to standard construction||7|
|Durability||Can withstand minor abuse||8|
|Use of recycled materials||Substantially less embodied energy than standard construction||9|
|Cost||Less than $300||10|
Consideration: potential for the wall as an education tool in green-building
Materials and Retail Costs
|Quantity||Material||Source||Cost ($)||Total ($)|
|3||94 lb bags portland cement||Pierson Building Center||0.00||0.00|
|0.5||cubic yard of masonry sand||Eureka sand and gravel||0.00||0.00|
|4.5||cubic feet of saw dust||no provider yet||0.00||0.00|
|4||50 lb bag of hydrated lime||Do-it-best hardware||8.50 at discount||34.00|
|0.25||cord of Western red cedar||Almquist Lumber||300.00||81.00|
Tools to be barrowed from CCAT
- wheel barrow
- chain saw
- hand saw
- garden hoe
- splitting wedge
- sledge hammer
- measuring tape
Proposed Time Line
- 3/5/10-pick up sand and sawdust samples (sawdust will have to tested to determine suitability)
- 3/5/10-get wood delivered
- 3/6/10-make at least 4 test samples of mortar. (We need to test the effectiveness of the cement retardant and appropriate water ratio)
- 3/8/10-see which test sample have dried. Scratch and them break the dry ones to test for durability.
- 3/12/10-make more test samples. Failure of all previous sample is a possibility.
- 3/12/10-saw several of the logs to right length and split into quarters. Let them dry some over spring break.
- 3/22/10-We hope to have determined the right mortar recipe by this time. If so about 4.5 cubic yards of the right sawdust or paper will be picked up.
- 4/2/10-lay down the first and maybe second layer of cordwood and mortar. Split wood for next week
- 4/9/10-keep laying cordwood.
- 4/16/10-keep laying cordwood.
- 4/23/10-finish here.
Some lessons learned
Cordwood construction is not very difficult, but it is best done with lots of help. Doing this alone on some days made for comparatively slow progress. It helps to have a helper on the other side of the wall so that you don't have to run around the wall just to check if the log is still in the right place. Get volunteer help.
Use a level or a plum bob to ensure that that wall goes up straight. This is especially important with lots of volunteer labor. Placing a log quarter inch too far is not a big deal, but this can add up to a leaning wall.
Don't try to do a perfect job on each log. I mean that each log should be put in squarly, but don't spend too much time making the mortar pretty, known as pointing. You can go back latter and do the fine mortar work after you have done 10 logs or so. Better yet designate some people to be pointers and others to be the rough masons.Marques: I found that it is essential to use gloves when handling the mortar. The lime in the mixture made my hands very dry. and like Garret I really believe in a group effort. the job is not a hard one but it is a tedious one and having a few people to help is essential. Another thing I learned was that it was easier to do a few logs and the after going back with the butter knife and pointing(touching up, beautifying the mortar wit the log so it looks smooth).
Updates October 2013
The only thing we’ve done to this wall as well, is patched up a little bit of morter around some of the wood logs. This was due to weather and settling. Also, some of the logs have shrunk and separated a little bit from the mortar. This is also due to loss of water due to high temperatures, and sun exposure. But this has caused no issues to the structure of the wall at all. This is only apparent on the side of the wall facing the elements. On the inside of the shed, there is no evidence of wood shrinkage. And no light or water is seeping through.
Cordwood is at best a mostly "green" building method, since it uses a good deal of Portland cement. Appropriateness is limited by a few factors. First the wood used should be waste wood. There's no point in cutting up perfectly good lumber into 16" long pieces. In addition the wood must be a species that has low shrinkage and high rot resistance. Not any old stack of firewood will do! Second it is best if the timber has a strait grain so that it can be split, however, I suspect waste wood could come from strait trees with a twisted grain. Logs with twisted grain might be used if only rounds are used in the wall. In short, for cordwood to be appropriate you need a very particular source of waste wood. This project used primarily cedar, of which there is at least one native species in the Humboldt Bay region. Again, it should be reiterated the importance of the type of wood involved in this project: it must be rot resistant, straight grained.
One interesting source mentioned in Cordwood: State of the Art was waste cores from plywood manufacturing plants. If the wood is the right species, such plants might be a gold mine of waste wood.