Compressed Earth Blocks - Open Source Ecology

25.09.2012 Compressed Earth Blocks - Open Source Ecology

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Compressed Earth Blocks

From Open Source Ecology

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Contents

1 Overview

2 Materials used in compressed earth blocks

2.1 CEB Shapes and Sizes

2.2 Alternative Materials2.3 Aesthetics

3 Advantages of CEBs3.1 Thermal properties

3.2 Comparison to other natural building methods

3.3 Local production3.4 Durability

3.4.1 Strength

3.4.2 Water Resistance

3.4.3 Fire and Mold-proof

3.5 Economics: The press, initial building cost, maintenance

3.5.1 Building Costs4 Disadvantages of CEBs

5 More Information6 References

Overview

Compressed Earth Blocks are the main construction material used in the GVCS Compressed Earth Block Press(formerly called The Liberator).

CEB Construction is a powerful technique for empowering communities to produce on-demand housing.

The bricks do not require curing - so a machine may churn out bricks on-site that can be continuously added tothe building. CEB lends itself to 100% onsite building material sourcing. The thermal insulation, sound insulation,and strength of the bricks are excellent.

CEBs can also be used in fences, cisterns, road paving, ovens, dams, thermal storage cisterns, silos, barns, dairyplant, bakery building, greenhouses, raised garden beds, etc.

Materials used in compressed earth blocks



Bricks pressed on The Liberator

CEBs are made from soil that is 15-40% non-expansive clay, 25-40% siltpowder, and 40-70% sharp sand tosmall gravel content. The more modernmachines do not require aggregate(rock) to make a strong soil block formost applications. Soil moisture contentranges from 4-12% by weight. Claywith a plasticity index (PI) of up to 25or 30 would be acceptable for mostapplications. The PI of the mixed soil(clay, silt and sand/gravel combined)should not exceed 12 to 15; that is thedifference between the Upper andLower Atterberg limits, as determined

by laboratory testing.[1]

Selection and preparation of the soil areimportant to getting the best results from a CEB press. See the CEB Blocks page.

CEB Shapes and Sizes

(TODO: Add pictures of CEBs built with The Liberator; show different shapes and sizes it can make)

To_Interlock_on_Not_to_Interlock

Alternative Materials

Krafterra: A researcher from UnB (University of Brasília, Brazil) suggests the use of kraft paper from

cement bags mixed with earth to obtain better CEBs, dubbed krafterra.WoolGeopolymers: Although cements are the most common application of geopolymerization, a range of

refractory and structural products have been produced. The products of geopolymerization are calledpoly-silicates.

Galvinized wire? Galvinized wire reinforcing would be light and could probably provide extra resistanceto earthquakes. The prices are similar to rebar per pound, but there is perhaps 5 times the support per

pound of material. Does not need double thickness, which cuts down on labor.

Aesthetics

MEB photo gallery (http://www.midwestearthbuilders.com/photogallery.html)

CebTex (http://cebtex.com/?page_id=6)CebTex2 (http://cebtex.com/?page_id=7)

exterior images AECT (http://pages.sbcglobal.net/fwehman/Exterior.html)interior images AECT (http://pages.sbcglobal.net/fwehman/Interior.html)

Midland Project Construction Pictures by Earthblock Texas Homes(http://www.adobemachine.com/midland_project_construction_pic.htm)

Stick frame construction is the main building method in North America. It is a weak but fast building method,which makes money for developers but returns little value to the homeowner, if one considers lifecycle cost of



buildings. (note the lifecycle use of materials in Greenforms at CMPBS) Procuring lumber drains money out oflocal economies. This is not to mention clear-cutting and vast lumber monocultures that supply the lumber. Weare interested in raising the standard of building, away from stick frame. We believe that with all theseconsiderations, the CEB is the only building technique that even remotely has a chance of substituting for stickframe constuction, and that with our machine, priced $3-5k and designed for fabrication replication, will fill in agreat need. CEB construction has the potential for mainstreamability in home construction.

Advantages of CEBs

Thermal properties

CEBs are excellent thermal insulators. In very cold climates, a superinsulated building can be made by putting alayer of insulation between two layers of CEBs - see Superinsulated CEB Construction

Furthermore, they lose and gain heat less quickly than surrounding air. As a result of this, they store warmth incold weather, and coolness in hot weather.

Comparison to other natural building methods

If you want to build a home from natural materials, you have a choice of -

Wood: stick-frame, timber frame, post and beamStructural masonry: brick, concrete block, rock, CEB (note that CEB falls into the class of structural

masonry)Earth-mix: adobe, rammed earth, stabilized earth blocks, cob, earthbag

Other natural building methods: strawbale, cordwood, papercrete, earthships and variations of all types.

Earthbag and cordwood construction, though cheap, take too much time. It takes about $400 and 400 man-

hours to build the walls and roof of a 200 square foot (18.6m2) room. Earthbag construction requires filling,stacking and tamping bags of earth. As the walls get higher, the bags must be lifted accordingly. Barbed wire isstrung between layers of bags. The process is not easily mechanized. And the walls require stuccoingafterwards. Cordwood was also difficult. Wood has to be cut, stacked, restacked and stacked again. We weresurprised at how much wood was required for a small addition. Furthermore, both cordwood and earthbagshave the distinct disadvantage of being irregular. By contrast, CEB construction takes much less time. This isbecause the blocks made are uniform, whereas other natural building methods use irregular materials.

Wayne Nelson of Habitat for Humanity in his piece entitled "Compressed Earth Blocks"(http://www.networkearth.org/naturalbuilding/ceb.html) says, "Uniformly sized building components can result inless waste, faster construction and the possibility of using other pre-made components or modular manufacturedbuilding elements." High uniformity gives CEB a competitive advantage over other natural building methods,allowing the CEB to influence local economies as a building medium.

Local production

Compressed earth blocks exemplify the quality "locally-made". The required clay-sand subsoil is locallyavailable nearly everywhere. Even the mortar is made from this mix with additional water. (See: Wikipedia(http://en.wikipedia.org/wiki/Compressed_earth_block) ) Humus-rich top-soil can be preserved for agricultureand the resulting hole may become a basement, root-cellar, pond or smoothed out to blend with the landscape.



If onsite soil is insufficient (ie. not enough, or unbalanced) near-by off-site soil or ammendments might be anappropriate option. Miles traveled: near Zero.

Compare this to the stick-frame house. According to "Gate-to-Gate Life-Cycle Inventory of Softwood LumberProduction" by Michael R. Milota, Cynthia D. West, and Ian D. Hartley, lumber travels 65 miles on average,just to get to the mill. Numerous unnatural materials are often used (ie vinyl siding and insulation) that have theirown set of negative ecological consequences.

Other natural building methods have variably high scores on local, ecological use of materials, provided thematerials are locally abundant.

A CEB press also can also enhance the local economy through a brickworks facitility. Bricks can be madecompetitively at a local scale. In "Compressed Earth Block Volume 1: Manual of Production" by CRA Terre,Vincent Rigassi (see D.10) (http://80.237.211.43/basin/publications/index.asp?A=1) , CEB is pronounced as"one of those rare 'modern materials' which has sufficient production flexibility to enable it to be integrated intoboth formal and informal sectors of activity, from 'cottage' industry to full-scale industrial plants" (pg 5).

The third opportunity for local production is to manufacture CEB presses. Our open-source CEB machine TheLiberator is designed to be built with simple tools and off-the-shelf parts. There is an opportunity for hugeprofits here as other CEB presses are expensive ($25k for one of 3-5 brick/minute performance). TheLiberator's design has minimum welds, using only bolts to secure the frame together. Since no specialized toolsor advanced skills are needed, a local machine shop or adventurous entrepreneur can easily manufacture it,contributing to the local economy.

Durability

Strength

Strength of CEBs depends on the machine (especially automated versus manual) and the quality of the soil(poorly mixed soil can lead to a weaker brick). According to Wikipedia, "CEB can have a compressive strengthas high as 2,000 pounds per square inch. Blocks with compressive strengths of 1,200 to 1,400 p.s.i. arecommon." We have not yet strength-tested blocks from The Liberator.

The compressive strength of CEB sounds impressive, but according to Fred Webster, Ph.D. seismic Engineer inhis paper "Some Thoughts on'Adobe Codes' (http://www.deatech.com/natural/cobinfo/adobe.html) , it is neitherthe only nor the most important variable in determining the ability of CEB's to withstand loads. "In actuality, highcompressive strength is and should not be the greatest concern related to pressed block quality. If the block hasa compressive strength of 1000 psi rather than 300 psi, it is quite superfluous to the performance of the buildingsubjected to ordinary service loads or even earthquake loads. It is not requisite that earthen blocks be up to thestandard of concrete in order to perform well during severe earthquake shaking." Webster suggests that soilquality may be more important than compressive strength in determining the bricks overall durability. "Standardsfor appropriate soil selection need to be aggressively and rationally developed and tested by the pressed blockindustry. Currently, the best standards and research are being performed by BASIN(http://80.237.211.43/basin/basin/index.asp?A=1) , a combined appropriate technology effort made up ofGermany, England, Switzerland, and France" (Webster).

Water Resistance

Although high quality blocks are water-resistant, they are not fully waterproof and commercial builders, such asMidwest Earth Builders (http://www.midwestearthbuilders.com/) use a stucco to protect the exterior walls.Other design features, such as a large overhang, can also provide some protection against weathering.



CEB buildings may need to be re-finished with stucco coating, just like a house would occasionally need newpaint. If a conventional roof is used, maintenance repairs would be identical to a traditional house. Moreresearch is needed on maintenance costs of a CEB building.

Fire and Mold-proof

Economics: The press, initial building cost, maintenance

We have found that earthbag and cordwood costs about $30 per square foot ($322 per square meter) wherelabour is valued at $10/ hour. CEB construction should be about 5 times cheaper than that; data to follow.

The main cost is the machine for making the CEBs. Commercial versions that make 3-5 blocks a minute cost$25k. This is one reason why we have built The Liberator, an open-source CEB machine that costs $3-5k andcan make 9 blocks a minute.

A tractor with loader and rototiller are required to prepare the soil. These are additional costs. Other equipmentand their related costs are detailed in the pdf CEB manual D.10(http://80.237.211.43/basin/publications/index.asp?A=1) found on the BASIN website.

Building Costs

MEB (http://www.midwestearthbuilders.com/BuildingInfo.html) claims, "[c]ost on a per block basis averageapproximately $1.10 per block. A 1000 square foot home will need approximately 5,500 blocks. So, $6,050would be the block costs. Once again, we have worked with customers who have provided their own labor andtractor for loading, and have brought this cost down to $.50 to $.60/block."

CEB press maker AECT (http://pages.sbcglobal.net/fwehman/AECTOverview.html) claims, "the cost of thestructural compressed earth block construction using the AECT structural compressed earth block machines toproduce the structural masonry blocks is between 25-40% less expensive than the next closest constructionapproach for quality, long lasting and energy efficient structures. Some other cheaper construction techniquesare inexpensive, but the resulting housing or commercial buildings are cheap, structurally deficient, noisy, andwasteful in energy use and not appealing to homeowners or commercial tenants."

But when compared strictly on economic terms to a conventional home, natural building methods savesurprisingly little. Most natural building methods use convential roofs and foundations. Only the walls areconstructed from alternative materials.

From their experience, Midwest Earth Builders (MEB)(http://www.midwestearthbuilders.com/BuildingInfo.html) claim "Because CEBs are used entirely as a wallsystem, the remaining costs, which can represent 80-90% of the total cost of the home, will be the same asconventional building. For example, the cost of the roof, windows, cabinets, etc. are the same for a framed andCEB home.

Building the wall of a home typically represents 10-20% of the total cost of a home. A CEB wall will average15% more then a conventionally built wall. In other words if the wall of a conventional home cost $15,000 for a$100,000 home, it will cost $2,250 more for a CEB wall."

A similar summary of straw bale housing is given from Green Home Building(http://www.greenhomebuilding.com/strawbale.htm) . "Erecting bale walls can go amazingly quickly, and doesnot take a lot of skill, but then the rest of the creation of the building is similar to any other wood framed house.In fact strawbale houses typically only save about 15% of the wood used in a conventionally framed house. The



cost of finishing a strawbale house can often exceed that of standard construction, because of the specializedwork that goes into plastering both sides of the walls. The result is often worth it though, because of the superiorinsulation and wall depth that is achieved."

A commerical, pre-built 200 sq ft "deluxe shed" (http://www.philssheds.com/sheds.htm#Deluxe) costs $4,400.Missouri minimum wage is $6.50, but if we gave the workers a nice $10/hour, the price is equivalent. (Anothercompany (http://www.postwoodworking.com/shed_pricing.asp) quoted their shed at $4,009 and I found a two-year old aluminum one on craigslist for $1500, which was originally bought at $2500.)

Other points to consider:

1. Skill level. Stuccoing straw bale buildings may be better left to a professional. CEB requires little skill and

is therefore, a good choice for the owner-builder. Normal masonary work requires skilled professionals

to apply a thick (1/4-1/2") layer of mortar between layers of bricks, but "because earth blocks do notrequire thick mortar joints, walls can be built quickly by workers unskilled in masonry" (MEB)

(http://www.midwestearthbuilders.com/BuildingInfo.html) . MEB

(http://www.midwestearthbuilders.com/AboutUs.html) explains, "One does not have to be an

experienced mason to build with CEBs. Homeowners, contractors, and builders can quickly be taught

how to stack a wall and begin construction immediately. Because only a thin mortar/slurry joint is used

between blocks, walls go up quickly and there is no need to wait for the mortar to set up after a few rows

like with typical brick masonry."2. Can other parts of the building be made more economically? CEB can be made into roofing shingles with

a roof-tile mold D.10 (http://80.237.211.43/basin/publications/index.asp?A=1) . Conventional roofs are

easily held by CEB: "If the block has a compressive strength of 1000 psi rather than 300 psi, it is quite

superfluous to the performance of the building subjected to ordinary service loads or even earthquake

loads" (Webster) (http://www.deatech.com/natural/cobinfo/adobe.html) . Thus, it seems safe to assume

that a CEB wall, appropriately constructed, could hold up the weight of a living roof. Although again, with

current technologies, it is more expensive up-front, with long-term savings in maintenance and heating.3. Because CEB is an on-site material and because all parts of the process can be done by hand or

machine, it lends itself to great variability of final product prices. Habitat for Humanity

(http://www.networkearth.org/naturalbuilding/ceb.html) uses CEB in some of their projects. And BASIN

(http://80.237.211.43/basin/partner/index.asp?A=1) is comprised of organizations which do development

work. So, obviously, CEB homes do NOT need to cost as much as conventionally-built ones.

Disadvantages of CEBs

The CEB does fall short of perfection in a couple respects. The press and other needed equipment (ie. rototillerand tractor) are not made from locally harvested materials. However, almost all building methods require use ofsome heavy machinery, and to its advantage, the press is designed to be locally manufactured. Also, TheLiberator is not designed to make roofing shingles (although these can be made from compressed earth). So,the ecological qualities of the roof cannot be addressed.

More Information

CEB Press - Full information on our high-performance, low-cost, open-source CEB machine: The

Liberator.

The Liberator Full Product Release

Earthquake safety

CEB FAQ (http://www.institutotierraycal.org/CompressedEarthBlocks.html) from Instituto Tierra y Cal



100-page CEB handbook (http://unesdoc.unesco.org/images/0012/001282/128236e.pdf) from a

Unesco project in SudanOverview of CEBs (http://www.earthblockinc.com/overview.htm) , by Jim Hallock

What should we have in mind when acquiring a CEB press? (http://www.tijol-eco.com.br/infos.html) -

CEB legal issues and norms in Brazil

appropedia: Compressed earth brick press

Auram earth construction equipment and blocks (http://www.earth-auroville.com/index.php?

nav=menu&pg=auram&id1=7&lang_code=en) from Auroville Earth Institute (available in many shapes).

Rammed Earth Construction (http://autonopedia.org/buildings_and_shelter/Rammed_Earth.html) fromAutonopedia

Rammed/Stabilized Earth (http://www.whygreenbuildings.com/ecolodgical/page.php?pageID=131) from

Green Building Encyclopedia

Advanced Earthen Construction Technologies (http://pages.sbcglobal.net/fwehman/)

Powell and Sons CEB machines (http://www.adobemachine.com/)

Gernot Minke - one of the world's leaders in earth construction - see here

(http://www.eartharchitecture.org/index.php?/archives/786-Gernot-Minke.html) for thorough overview,

including detailed soil testing procedures.Galvanized wire reinforced, earthquake resistant earth construction techniques publication - [1]

(http://sheltercentre.org/sites/default/files/GalvanisedWireReinforcement.pdf)

Ronald Rael is an Architect, Author and Assistant Professor of Architecture at The University of

California, Berkeley. He is the founder of EarthArchitecture.org (http://www.eartharchitecture.org) , a

clearinghouse of information on the subject.

Compressed Earth Block Guide - [2] (http://nzdl.sadl.uleth.ca/cgi-bin/library?e=d-00000-00---off-0cdl-

-00-0--0-10-0---0---0prompt-10---4-------0-1l--11-en-50---20-about---00-0-1-00-0-0-11-1-0utfZz-8-00&a=d&c=cdl&cl=CL2.3&d=HASH01979938ef89e979ddfb736b.9.2)

GTZ manuals on CEB technology: Volume I, Manual of Production

(http://www.sheltercentre.org/library/Compressed+Earth+Blocks+Volume+1+Manual+Of+Production)

and Volume II, Manual of Design and Construction (http://sheltercentre.org/library/compressed-earth-

blocks-volume-2-manuel-design-and-construction)

Other information - [3] (http://www.grisb.org/publications/pub34.htm) , [4]

(http://www.earthblockinc.com/faq.htm)

References

1. ↑ http://en.wikipedia.org/wiki/Compressed_earth_block

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