Uses, Properties, and Sources of Natural Building Materials



Uses, Properties, and Sources of Natural Building Materials

a partial list by Michael G. Smith

|Material |Uses |Properties |Sources |What to look for |

|Clay |Binder in all earthen building |Sticky when wet; bonds to many other |Harvest a clay-rich soil from site excavation, road |For many apps (cob, adobe, etc.) a low-purity clay soil is fine. |

| |materials, including cob, adobe, |materials; expands when wet; shrinks |cuts, river or stream banks, ponds, etc. |Subsoils (low organic content) from many places are good. For some|

| |rammed earth, light-clay, earthen |and cracks when dry; absorbs water; |Purchase powder in bags (white Kaolin very good for |apps (especially plasters, paints, slip for light clay) a fairly |

| |floors and plasters, daub, alis |soft when wet, hard when dry; |paints and plasters) |pure source is desired. Use commercial source or high clay |

| |paint |malleable; many kinds and colors |Purchase potter's clay (offcuts often available free |deposits from river banks, etc. Be careful of environmental impact|

| | | |from ceramics studios) |of harvesting from wetlands. |

|Straw |Fiber in cob, adobe, light-clay, |High tensile strength; good |Buy direct from grower (organic sometimes available) |Most grain straws (rice, wheat, oats, barley, etc.) are good. Rice|

| |daub, clay wattle, earthen |insulation (contains air); absorbs |Buy from feed store (loose straw often available free|straw especially high strength. All straw must be fresh or stored |

| |plaster, earthen floors; baled in |water; encourages migration of water;|if you pick it up the floor) |dry; it loses fiber strength if it gets wet; don't use moldy straw|

| |walls; insulation; thatching |breaks down rapidly when wet; light |Grow and harvest your own (this may be the only |ever. Bales for building should be very tight. For some apps (clay|

| | |weight |option when very long straw is needed, as for |wattle, cob corbeling, and especially thatching), long straw is |

| | | |thatching, since commercial grain varieties are short|important. For others (plasters, finish floors) you need short |

| | | |and often chopped up during harvest) |straw; chop with chipper, compost mulcher, weed whacker, or |

| | | | |machete and screen. |

Material |Uses |Properties |Sources |What to look for | |

|Sand |Aggregate in cob, adobe, rammed |Hard (high compressive strength); |Buy from sand and gravel yard (main sources are river|For structural apps (cob, rammed earth, mortars, floors, base |

| |earth, mortars, plasters |stable (does not expand or shrink); |banks; quarries; or sometimes glacial deposits) |plasters) fairly coarse, angular sand is best. Sand made by |

| | |does not hold water or deteriorate |Harvest and screen from creek or river banks |crusher is roughest, then river sand. A wide range of particle |

| | |when wet; heavy |Harvest from beach |sizes is good. Don't use fine beach or dune sand except for highly|

| | | | |polished finish plasters and floors. |

|Gravel |Drainage (rubble trench, French |Hard (high compressive strength); |Buy from sand and gravel yard (main sources are river|For drainage, use coarse clean gravel (1.5" to 3" best), round |

| |drain, under adobe floors); |stable (does not expand or shrink); |banks, quarry, or sometimes glacial deposits) |river or glacial gravel is best (but be aware of environmental |

| |sometimes aggregate in earthen |does not deteriorate when wet; lots |Harvest and screen from creek or river banks |impacts of harvesting); "cut rock" from quarry is OK. For |

| |floors, cob, rammed earth |of air space for drainage; heavy | |aggregate, quarry rock is good, mixed sizes are good. "Road base" |

| | | | |is an engineered mix of aggregate sizes. |

|Stone |Foundations; walls; sometimes |Hard (high compressive strength); |Harvest your own (cheap but labor intensive) |For foundations and walls, a hard, sound stone is desired (doesn't|

| |filler in cob; flat flagstone for |stable (does not expand or shrink); |Buy direct from quarry |crack or crumble). Some kinds (sandstone, etc.) break naturally |

| |floors and walkways |does not deteriorate when wet; heavy |Buy from masonry supplier (many choices, but |into flat pieces, making them especially easy to stack. |

| | | |expensive) |Alternatively, consider recycled comcrete chunks ("Urbanite"). |

|Wood, round |General structure: posts, beams, |High tensile strength; easy to cut |Harvest from wooded areas, especially former |Wood should be free of rot. Remove bark. Some woods (redwood, |

| |rafters; cut short for cordwood |and fasten; flexible when thin; prone|clearcuts |cedar, locust, etc.) much more rot resistant. Soft woods |

| |masonry; wattle; railings and |to rot when wet |Logging "waste" |(conifers, alder, etc.) easier to work. Hard woods (oak, maple, |

| |decorative | |Coppice (cut back certain tree species to encourage |madrone, etc.) more durable. Coppicing requires intensive mgmt. |

| | | |growth of straight, flexible, shoots) | |

Material |Uses |Properties |Sources |What to look for | |

|Wood, milled |General construction: structure, |High tensile strenght; easy to cut |Buy from sustainable mill |Should be rot-free. Be aware that most commercial lumber is |

| |floors, ceilings, furniture, etc. |and fasten; extremely versatile; |But from building supply |harvested very unsustainably. Treated wood products are highly |

| | |prone to rot when wet |Mill your own |toxic. |

|Wood chips |Fiber for light-clay |Short fiber; prone to rot when wet |Run logging slash or milling waste through chipper |Should be coarse and relatively free or bark and leaves. |

| | | |Free from road crews | |

|Sawdust |Insulation; additive to mortar for|Light weight and insulative; absorbs |By-product of saw mill or woodworking |Should be clean (free or dirt and bark). Sawdust from furniture |

| |cordwood |moisture; breaks down when wet | |shops, etc. may contain glues and chemicals. |

|Manure, cow or |Fiber for earthen plasters and |Very fine fiber; enzymes enhance |Collect from stable or pasture |Horse manure fiber slightly longer than cow. Use either very fresh|

|horse |floors |workability and water resistance; | |and soft, or dry but still green inside. If hard, can be grated |

| | |absorbs moisture; breaks down when | |through a screen or mixed with a paint mixer in water. Do not use |

| | |wet | |if moldy. |

|Bamboo |Structural: trusses, etc.; pins |Very high tensile strength; flexible;|Grow your own |Many different varieties and qualities. Proper harvesting, |

| |for straw bale; wattle; decorative|fast-growing; cracks in dry |Harvest from established groves |storage, treatment and joinery require knowledge and care. |

| | |conditions; short life unless |Buy from supplier (usually imported from Asia) | |

| | |protected | | |

|Reeds |Thatching |Very weather-resistant; long |Harvest from wetlands |Only certain species appropriate for thatching. Huge quantities |

| | | | |needed. Harvesting by hand very labor-intensive. |

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