About Natural Building Straw Bale Cob Other Walls Plastering
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Whispering Seed

source: Tim Reith

Other Natural Wall Systems

In reading through all of the pages in this website, a few themes become apparent: natural materials tend to be very inexpensive, yet labor intensive; these materials respond well to moisture when well-designed, and are not served — and are often harmed — by the presence of vapor barriers; most notably, a basic set of ingredients — clay, sand, straw — keep appearing in various proportions to serve various functions. It is this last theme that is one of the most important in the world of natural building — the ability to use a small set of basic materials, each for their desired attributes, in varied proportion to get a wide range of building materials to be placed in different contexts. Structural walls, subfloors, finish floors, rough plasters, fine plasters, fine paints and washes, insulation, infill panels, patching compounds — all from clay, sand, and straw. Keep this in mind as we take a look at some of the many other applications of natural building techniques, and please remember that this is by no means a comprehensive list, only a sampling of the more common techniques found in this climate:

Light Straw-Clay (AKA Slip-Straw)
One of the oldest common forms of straw in building, this material was originally known as leichtlehm, German for "light loam". Its historic use has been best highlighted in the old Tudor mansions of what is now Germany, where it was used as infill panels in the timber frames, and finished with white-washed lime plasters. This is one of the most basic natural building materials, consisting simply of loose straw coated minimally in clay slip (clay diluted with water to the consistency of a milkshake). Slip-straw is used not as a structural wall system, but as an infill panel built between framing members. Slip-straw is tamped by hand or with a stick in between 'slip forms' — forms placed on either side of the wall cavity, which are then removed after being filled and refastened further up the wall. Walls are finished with plaster. Being made primarily of straw, slip-straw walls tend to be well-insulating, although not as well as straw bale.
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Woodchip-Clay (AKA Slip-Chip)
A variation on slip-straw, slip-chip walls are bark-free woodchips of various sizes (from sawdust up to 1-2" chunks) that are similarly coated in clay slip, and poured into forms. Strong advantages of slip-chip in this climate are the abundant wood resource (wood chips are a common by-product of multiple regional industries), the ease of mixing (easily done in a mortar mixer, as opposed to by hand or custom machine for slip-straw), and ease of installation (easier to tamp). The forms, however, must be permanent — slip forms will not work. The most common strategy is to use wood lath, similar to pre-sheetrock lath-and-plaster walls, which can then be plastered. Best practices for slip-chip walls are still in development, and much has yet to be learned about their performance in this climate, although early empirical experience points favorably towards their long-term success.
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Adobe, Compressed Earth Block, Earthbag, Rammed Earth (pisé)
Earthen construction is not common in the northeast, but should be mentioned nonetheless, as it is still a viable option for those interested. Adobe block, found more commonly in the southwestern US, is made of pre-cast blocks formed of clay soil (an appropriate proportion of clay and sand) and chopped straw. Variations on the traditional adobe block run wide, a common one being essentially a slip-straw block, providing improved insulation but without structural capability. Compressed earth blocks would be a category to which traditional adobe block would belong; quite often, compressed earth blocks refer to compressed stabilized earth blocks, or earth that has about 10% cement mixed in and pre-cast into blocks for building. Earthbags, as detailed in the foundations section, follows along similar themes, using polypropylene bags or tubes as forms that are filled in place and stacked. Rammed earth — also known as pisé, or pisé de terre — is akin to building a cement wall with earth: soil in correct proportion of clay, sand, and gravel, often with a stabilizer (traditionally lime or animal blood, now commonly cement), is tamped (or 'rammed') into forms that are then removed, and the monolithic wall is left to dry. Similar conclusions of the appropriate use of these earthen materials can be drawn by looking at cob, particularly in regards to ecological benefit, thermal and moisture properties, and cost.
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Wattle and Daub
Another ancient material, wattle and daub has cropped up everywhere in the world, throughout time. It is essentially the first drywall; drywall was made to replace plastered wood lath (thin strips of wood nailed to framing). Before there was wood lath over stick framing, people made walls of woven sticks, reeds, or other similar material — the 'wattle' — and plastered it with clay or manure plasters — 'the daub'. While some of the vertical wattles could be made structural, this is generally an infill wall panel technique. Note that the walls are generally relatively thin (compared to many natural walls, such as straw bale or cob), and are therefore less massive then there pure-earthen counterparts (although the 'daub' can be built out to be quite thick). These walls also hold very little insulative value, if any. While generally impractical in this climate for exterior walls, wattle and daub walls make terrific interior partition walls, railings, or other lightweight and inexpensive dividing structures.
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Cordwood Masonry
Also known as 'stackwood' or 'stackwall', these walls are built of rounds of wood ('cordwood' being a reference to firewood, a 'cord' being a measurement of stacked wood) that are mortared together to create a visually stimulating and structural wall. Walls are either one or two logs deep; in the former, the 12-24" logs (generally 4-10" in diameter, but can range very widely, and splits can be used as well) are bedded in mortar on either side of the log, with the interior filled with sawdust or other insulation material. In the latter, an insulation cavity is created between the two walls, allowing for a wall that is of greater thermal performance in our climate. The mortar can be made either of cement, lime, a combination thereof, or even cob. These walls also contain significant mass, although again not as much as earthen walls. The insulative value is limited by the thermal bridging of the logs (generally assumed to be approximately R-1 per inch) running from the interior to the exterior, but longer log lengths or double-wall construction will improve the insulation. Cordwood, another historic building technique, has also been enjoying a revival, the epicenter of which is in northern New York; therefore, an abundance of such buildings — as well as those will knowledge pertaining to their construction, and materials with which to build them — are readily available in the northeastern US.
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Earthen Ovens and Rocket Stoves
Not to be overlooked, in addition to all the walls we have mentioned are the many other things that can be built of these materials. While the list of potential projects is as long as the imagination, there is a particularly strong application of earthen materials in the realm of fire. Earthen ovens — sometimes referred to as cob ovens — are as ancient as baking, and are prevalent in indigenous and colonial cultures alike throughout humanity, and still hold great relevance today; some of the best bread and pizza available is built in such ovens. These ovens are just as they sound: formed of earth, often with a layer of insulation made of straw, sawdust, perlite, or other similar material, and plastered. There are two traditional ways of building these ovens: one is to make a mold of sand, upon which the oven is built, and after which is removed through the oven door. The other is the Quebec-style oven, in which the form is built of alder saplings bent into a 'bender', or hemispherical shape, upon which the oven is built, and after which is burned out in the first fire. Fires are built in the ovens, raked out, and then bread is placed onto the hot hearth to bake in the radiant environment. Rocket stoves were created to replace traditional open-fire cooking methods that were very unhealthy to occupants in indoor environments; they are simple designs incorporating a burn chamber, a chimney, and a heat exchanger, that burns fuel incredibly efficiently, leaving few combusted pollutants and gleaning the most heat available from the fuel. In western applications, these stoves have been modified for use as heating appliances, and can be readily built of cob and sculpted into walls, heated benches, or other creative fashions.
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Stone
It may be taken for granted that stone building is natural building in some of its purest form — taking raw materials, preferably from on site, and building structures of beauty and function with simple tools. Whether building full houses of stone, using stone as roofing material, building masonry heaters or stoves of stone, using stone for flooring, countertops, or other horizontal surfaces, or dry-stacking or mortaring stones for foundations, stone is a very relevant and indispensable material in the lexicon of natural building, and well-deserving of a place in most any structure. Whether sand, gravel, fieldstone, or slate, we would not be building were it not for rock.
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