Build a Home Using Alternative Building Materials
Low-Cost Construction Techniques That Use Materials From the Earth
Reading Time: 11 minutes
By Charmaine R. Taylor — Building a self-sustaining home or structure is a wonderful concept that can be put into practice by anyone looking to create shelter for man or animal. Homesteaders and people seeking a self-sustaining living are amazingly ingenious at discovering alternative building materials to store-bought, high-priced, over-processed goods. And the “waste” generated by our consumerist culture makes for a happy hunting ground across the entire country. Most of us know how to scrounge for windows and doors, recycle, and barter for used cabinets, fixtures, yard sale and demolition materials in order to build a self-sustaining home from alternative building materials. But beyond that are truly free building materials generated by the Earth herself.
Building with Earth
Using earth to make walls and houses has been done for thousands of years. It isn’t a new concept in the US either. In the 1920s, the US government promoted rammed earth for farm buildings and produced booklets on soil testing, adobe brick making, and earthen house construction. In the 1970s, Ken Kern actively experimented and wrote about clay-lime-straw-asphalt emulsion formulas for hand-built walls. He created several curved, passive solar buildings on his homestead in California using free alternative building materials. His books taught owner-builders to experiment and use on-site, healthy materials for their self-sustaining homes.
Clay, sand, rocks, straw, woodchips, sawdust and even weeds can be put to used as alternative building materials to build the entire self-sustaining home. And that is the beauty of using nature’s gifts — readily available, unwanted and uncommercialized, with no profit in restricting your access to grass, weeds, river or beach sand, clay or rubble. In fact, clearing away scrap shrub and weeds is seen as an improvement to most property! Most of what you need can be found in your own backyard, down the road, or in a local field or stream. The only item which must be purchased for some of the building mixes described here is hydrated lime, sold in 50-pound sacks, at supply and home improvement retailers or feed & grain stores.
The Basic Alternative Building Materials
Clay: Clay is a very fine particle ingredient in an earthen mix. There are many classifications of clay based on its plasticity (ability to hold water), from very sticky “gumbo” clay which is a gray color, usually found lining river and stream beds, to kaolinite, which holds the least amount of water. Kaolinite (also called fire clay or mortar clay) is used for china and pottery, and by artists to make fired ceramics because it shrinks and cracks the least. Most regions in the US will have some type of clay under the topsoil. If there is none on your property the best way to locate it is to look for deep road cuts where construction is going on. Or, the walls of a river bank or stream will usually yield the stickier gray-gold clays. Once found the clay can be treated in a couple different ways. It can be sun and air dried, then crushed and remixed with water when you’re ready to build. Or you can simply dump large chunks of fresh dug up clay into a drum and let it soak in water for months. Most clay will fall apart and become pudding-like, but gumbo clay will remain impervious to water unless broken up into small pieces. The chemical makeup of clay is alumina or silica “platelets” with an attraction to water. Evaporation of water is what causes severe cracking, and this is why lime is needed. Lime stabilizes the clay by changing the bonds clay has for water, making it hydrophobic, so swelling/shrinking is greatly reduced or eliminated. Lime also bonds with clay to form a “pozzolan,” a natural cement. The longer clay and lime are together the stronger the cement bond between them. If you live in a sandy soil area and want to experiment you can purchase finely powdered bagged kaolinite clay. A 50-pound sack, mined locally in Sacramento, CA, is $3, but it may be more expensive in your area. Mixing the fine kaolinite powder into clean water is easy, but wear a dust mask to prevent inhalation. You may already have a perfect 30 percent clay/70 percent sand subsoil on your property. This is great for making traditional earthen mixes, or for adding sawdust, woodchips, and lime to make alternative mixes. Experiment with what you have, make test bricks and handle the material to see how you like using it. There is no one right way to do it, and your available, indigenous materials may dictate your final results.
Sand: The best sand is clean and sharp, with a wide range of particle sizes (from 3 mm down to 100-micron fines.) Sand can be found near streams or the ocean, but beach sands are mostly round particles. However, when mixing clay and lime this sand works well. I have used only unwashed (salty) beach sand for my cob wood mixes with no problem. A local quarry or aggregate seller may have “reject” sands, available cheaply, which are great for earthen mixes.
Fiber: Straw or grass provide tensile strength. Straw has no food value to cattle and is considered a waste material. It should be dry and chopped to about 4″-8″ long. Grasses such as dried lawn clippings can be used. Remove seed heads or flowers and pods if possible, especially when they will be used in finish plasters. Straw can be finely screened, or animal hair, such as goat hair, can be used. The many interspersed fibers give a flexible strength, reducing cracks and preventing large fissures, or failure due to lateral movement.
Lime: Lime means burned limestone (CAO3, calcium carbonate) which has given off carbon dioxide during processing. Bagged, hydrated limes used for building are a tiny portion of the US market, so finding the right lime to purchase is sometimes difficult. There are many grades and varieties of lime, and it can be confusing to understand them. A high calcium lime sold in feed stores is perfectly acceptable to use, but Type N builder’s or Type S mason’s lime are considered better because they must meet ASTM standards for performance in construction. If you will be using lime to mix with clay soils the less expensive high calcium limes will work as well. Dolomitic limestone is also mined in abundance in the US, it is a blend of calcium and magnesium carbonate, and is specially pressure hydrated so it performs well. However, don’t purchase “aglime” selling for $2 per bag. This is just ground limestone and is unreactive with clay. Lime mixed with sand at 1:3 has been used for centuries as a mortar and plaster. It hardens back into limestone by reabsorbing carbon dioxide from the air. It is considered the best binder in the world and is very forgiving to work with. Lime does set up much slower than cement, but it is binding on a molecular level with clay and sand to form a durable, vapor permeable material. Lime should be soaked in a bucket of clean water for as long as possible, for at least 48 hours to months, or longer. Buy lime which is less than six months old, maximum, so carbonation hasn’t begun in the bag. Fill a pail or drum one-third to one-half with water, and add the dry hydrated lime. Cover with a lid and let soak into a soft putty. The longer the soak, the more mellow and plastic the lime putty becomes. The saturated water on top can be drained off to make limewash, or to temper a dry mix. There is no need to stir the water back in, as with paint, as lime naturally gives up the water it doesn’t need. Lime is very drying to the skin but is not caustic or dangerous. Quicklime, not available to the general public, is highly reactive with water and can explode, so don’t mess with it unless you really know what you’re doing.
Adobe, Cob, Earthbag Rammed Earth, and Cinva Ram Bricks
The mixes described here range widely, depending on your building location. Most people have heard of adobe for bricks and houses in the Southwestern US, for instance, but very similar materials used in “cob” are not as well understood. Traditional adobe is a clayey, sandy soil, hand formed in molds to make bricks. There is no straw used in most adobe. Cob is a Welsh method using clay, sand, and long chopped straw to form and build walls. Sometimes cob is called monolithic adobe because it is one mass, not individual bricks. Cob can be constructed anywhere where there is adequate clay in the soil/sand ratio, preferably 30 percent. Digging out the footprint of the self-sustaining home will usually provide enough alternative building materials to build the walls. People use bales of waste straw in making cob, and roof ridge beams are often snow-warped trees, or scrap trees unusable for lumber. Earthbags are long sacks filled with poor soils and layered with barbed wire to bind them together. They can be covered over with an earthen plaster, and many designs incorporate a below grade floor. Misprinted rice bags are bought from manufacturers, and a shovel and coffee can are used for filling the sacks. Construction training is needed on this method to ensure the safe building of a self-sustaining home, however. Rammed earth became popular in the US in the 1920s when the federal government provided information to farmers on building fire-proof structures. A poor economy and few roads to transport lumber to rural areas made this a good solution. Harvested subsoil is stabilized with a small percentage of cement or lime, placed between a formwork of boards and tamped firmly. Often the wood forms can be used later for roof and floor construction. Manual and pneumatic tampers are employed, and several workers are needed to be efficient. Finished walls are protected by wide overhang roofs, or plastered with earth or lime. Rammed earth, and all earthen buildings (or Earthship homes), moderate temperature, are sound-proof, fire-proof and insect-resistant. Cinva-Ram bricks (compressed earth blocks) are made with a manual machine invented in Bogota, Columbia in the 1950s. Plain or stabilized subsoil is placed inside, then compressed and the bricks are cured before building. Much like adobe, with no added straw, these bricks are much stronger due to their density. Only a few individuals in the US manufacture Cinva-Ram machines, which cost between $650-$2,500; and you can buy plans to build your own. Automated brick-making machines can be rented; these produce thousands of bricks a day.
Alternative Building Material Mixes
Papercrete and paper adobe are also becoming popular alternative building materials. Papercrete is simply shredded paper, sand, and cement mixed in an industrial type blender. Paper adobe uses only shredded paper and clay to make a heavier material for bricks, blocks, and plasters. Once mixed this fibrous material can be poured between wall slip forms, or made into any size block, and left to dry in the sun like adobe. But it is much lighter when dry; insect and fire resistant, highly insulative, and mortars easily with papercrete mortar. Not counting foundation, windows, plumbing or electrical costs, some people have built for less than 35 cents a square foot with papercrete. The only cost is for Portland cement. Crestone, CO, and the City of the Sun, NM are two areas with several self-sustaining houses are built entirely of the alternative building material papercrete. This material is not code approved yet, and may never be due to the wide variety of formulation. However, sheds, workshops, self-sustaining homes for guests, offices, retreats, animal shelters and privacy walls have been built of papercrete. Most structures are built within the 120 sq. ft. county code restriction. Papercrete can look crude when unfinished, but when plastered over with a lime, earth, or even papercrete plaster it looks just like a regular house.
Using Other Fibers as Alternative Building Materials
Sawdust is already chopped and ready to use, and weeds, straw, and hemp are shredded and mixed in with clay or cement mixes to make very sturdy walls. Different tree species will produce a wide variety of sawdust. Some softwood sawdust is actually quite hard and grainy, more like sand. Conversely, hardwood sawdust will still absorb some moisture and may work quite well. Sawdust and woodchips will give up moisture as they age over several weeks. I have used Pacific Madrone, a hardwood, and Redwood, a softwood, and noticed no difference when combined with clay and lime. Sawdust also acts as an insulator and provides air entrainment which can help during freeze/thaw cycles. What is amazing is how simple it is to use these dry unwanted materials and create something practically for free. Clearing a weedy, overgrown, and hilly property could provide the filler material, and back-hoeing to make a level building spot can provide the clay, solving two problems and recycling two ingredients at one time.
Cobwood, Cobweed, Agstone and Stonehemp
Names for these mixes are arbitrary, of course, and only aid in confirming which mix was used for which project. I use locally dug up clay, bagged hydrated lime, and free local sawdust to make cobwood. Clay and lime together can make a strong stabilized alternative building material, or harden to a natural cement also known as Roman cement, an excellent eco-friendly binder, and it’s practically free. Cobwood and cobweed are similar, only the substitution of dried, chopped weeds for sawdust differs them. Woodchip and clay mixtures to make wall infill for timber frame self-sustaining homes have been used in Germany for centuries, and are popular again, and sawdust, sand, and cement have been used in Australia for decades. These walls are tamped like rammed earth, and once dry are solid, soundproof, and moderate temperature swings well. Agstone is California hemp papermaker John Stahl’s name for a recipe of hemp bast, or hurds, and miscellaneous dry weeds, mixed with lime, sand and Portland cement. Stonehemp is a name Canadians Dave Cull and Brad Davis are using for a mix which uses quicklime and industrial hemp, with, and without Portland cement.
Working Wet and Dry
The three primary ingredients of cobwood are mixed while wet, and all are measured by volume. A simple formula is 9-3-2-1. Wetted, aged sawdust (soaked overnight, then drained for a few hours), clay slurry, (thick as sour cream), lime putty (also like sour cream), and sand. Dry chopped grasses are added last before building. This pliant material can sit overnight, or for a day or so; is like a wet cob, and can be poured, hand applied, or thrown, “harled” as the Scots do with exterior renders. (Wear vinyl gloves.) My cobwood mix is high on sawdust because it is both freely available and comes ready-to-use, with no chopping necessary. Mixing is done by hand with a garden hoe, and clay is often slurried first with a paint stem mixer attached to a 1/4 HP hand drill. For larger construction projects a cement or mortar mixer can be used. The outdoor garden bench I built is made entirely of various experimental cobwood mixes poured over a rubblestone base of broken concrete chunks. Mixes were added one pail at a time and left to dry. Hand shaping of the back, arms, and seat was not difficult, and a form could have been used to build the base quickly. The design for a bench or seat can vary widely and could take any shape. Curved driftwood can be used for the arms, river stones can stud the base, and seashells or other elements can be embedded into the bench for more personal, creative expression. Thick cobwood can be poured between walls of wire mesh. Mesh can also be used as an armature to make a sculpture or as a form to build lawn borders or to frame raised garden beds. There are many possible uses for this material. I am not attempting to use cobwood for load bearing walls, or for critical structural areas, and I am not a construction engineer or architect. However, these natural materials have been used since the beginning of man’s (and woman’s) shelter building attempts, and are easy to play with for anyone interested in exploring alternative ideas.
Agstone maker John Stahl uses dry chopped weeds, shrubs, branches and donated hemp stalks as his filler material. Industrial hemp stalks, available in Canada and France, and weeds (available everywhere) make a great free filler. Dry brush, shrubs, teasel, yellow dock, even pine needles can be finely chopped and used. John Stahl has tossed newspapers and magazines into a wood chipper/shredder and used it along with weeds to make agstone. John uses Portland cement in his mixes, with a durable recipe being 10-4-3-2. Ten parts dry chopped hemp, weeds, straw; 4 parts dry lime hydrate; 3 parts sand, 2 parts Portland cement. He uses a wheelbarrow and adds ingredients by shovel, adding enough water to moisten, and hoeing the mix into a thick mass. While the cement isn’t being mixed according to package directions, I can’t argue with his success. John’s outdoor steps have been in daily use for over two years with no signs of breakdown. Each step is a different recipe, some with gypsum added, and one with no cement. The steps were poured into place, troweled smooth and left to cure. A limewash is coated on them once a year. John has also used formworks to make compost bins, a poured shed floor and is now constructing walls for a small building.
A brick, or wall or garden bench left completely exposed to driving rains will begin to return to the Earth. If lime was used in the mix any rainwater will cause less damage, but building under a tree for shelter, or plastering a wall for protection is best. Cob houses in England and Wales have endured for hundreds of years through extremely harsh winters. These self-sustaining homes were rendered with pure lime plasters and have stood the test of time. John Stahl does get below freezing temperatures in the mountains of Leggett, CA, and both of us endure long, very wet winters, and these natural materials have stood up well. Traditional cob will also perform well and saves adding lime or sawdust to the mix. If you can locate good soil, or mix sand and clay together for a respectable cob mix you will have a totally free building material. Lime, cement or purchased sand does add to the overall cost. However, when compared to other building methods, using these low-cost construction techniques and easy-to-use alternative building materials to construct a self-sustaining home or structure is fun, creative and practical.
Originally published in Countryside May/June 2001 and regularly vetted for accuracy.