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[Rob <becida AT comcast.net>]

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From: "tvoivozhd" <tvoivozd AT infi.net>
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Subject: Re: compressed earth block
Date: Sun, 18 Feb 2001 13:08:34 -0800
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> Do you know if there is any minimum psi needed to make a CEB?  While
> looking at the designs on the internet, I've seen a quite a variety of
> pressures being used.  I'm not sure how much pressure the manual CINVA
> rams generate, but I'd guess they have a compression of only about 30-50
> psi.  I may be way off on that, but the pictures typically show only a
> single person applying the pressure on the blocks with a lever about 6-8
> feet long.
>
> http://www.cinvaram.com/steps/step3.htm
>
> Maybe the higher the psi, the more stable the blocks?
>
> We just bought a larger tractor, that I believe could easily supply the
> power to make these blocks quite easily.  My first thought was to use
> the tractor to power a remote hydraulic cylinder.  This might be as good
> option, but I was thinking I might be able to build a simpler, less
> expensive unit by directly using the the power generated by the lift on
> the 3 point hitch.  I'm not sure how much force this might generate, but
> I believe it would be higher than that created by the manual CINVA
> units.
>
> Dan Settles

Tvoivozhd---there are no "minimums" in psi for making CEB, but the higher
the pressure the more dense is the block, therefore stronger.  What you are
trying to do is duplicate geological events which produce sandstone, and
make an economic tradeoff of compromise on density vs cost of producing
varying amounts of mechanical or hydraulic pressure.

Any of the manual CEB machines, from the original designed for low cost
housing in Colombia, to the present Aureka's, produce block dense enough to
last hundreds of years in a wall, vault or dome..  Yes, the hydraulic
presses may produce 50,000 psi, and yes the block is stronger, but such
pressures have only one advantage---you don't have to give much thought to
the proportions or constituents of soil elements used---staying away from
expansive clays of course..

Other than that it is overkill---like using inch and a quarter plywood for
stud-wall sheathing instead of quite suitable half inch sheathing..

Hydraulic cylinders are cheap, especially from the surplus houses.  I think
it would cost less and be more efficient to use one or two of these powered
by rear hydraulic lines of the tractor, rather than the three point lift.

Or modify a used woodsplitter---the kind that can tilt to a vertical
position.  I see them for sale in the local Trader every time a new issue
comes out..  As a variant on this theme, you can operate one of the manual
blockmakers with a hydraulic cylinder and some cobbled up linkage.

Going the hydraulic route has a much higher initial cost, but makes
production of CEB much easier and faster---harder to amortize the equipment
on a single house however, though a good percentage of its cost can be
recaptured by resale after completion of the job.

A rotary table machine is faster than a reciprocating press
(http://www.terstaram.com/ap3.htm) this particular one operates at 15,000 kg
pressure.

Of the domestic hydraulic presses, the Earth Press operates on a relatively
low 2500 psi block pressure, which still exceeds the UBC requirement for
block compressive strength.  http://www.adobe-block.com/

"The San Ysidro CEB press usually operate at 1700 psi, with a range from
zero to 2000 psi.  Pressure varies with quality of the mix used for block.
Q. how much pressure do you use to make a block?

A. This answer is dependent upon your moisture content and dirt quality.
With optimum dirt you would require about 1400 PSI to make a quality block
this is based on the formula: system pressure * cylinder area / area of
press foot a dryer mix would require more pressure and a wetter mix less.
Our machines a set to press at 1700 PSI. This is adjustable down to 0 and up
to 2000 PSI on the block as 2000 PSI is the maximum pressure capable the
wear on the machine would be considerably greater. "

The above San Ysidro is produced by Powell  http://www.adobemachine.com/

The specs change with change in hydraulic pressure and soil
composition---here is an excerpt from someone using 4000 psi in their
version of CEB---which increases block density of normal adobe mix (block
weighing 30 lbs) twenty five percent to a 40 pound weight.

The use of CEB permits great flexibility of design in a cheap, universally
available, strong and durable material---produced in machines of low to
moderate cost in relation to production capability.

It is a mental stretch a little broad for most builders, but you can
accomplish a similar result with a similar but uncompressed soil mix in
bags---where the requisite strength and durability is achieved not by
compression, not by reinforcement, but by temporarily turning the house into
a bake oven and ceramicizing the walls and roof with a barrel of oil,
gravity fed into a torch inserted in a door opening.  Nothing wrong with a
5000 square foot house built at a cost of $1800, with the most complicated
equipment being a funnel gadget used to fill the earthen bags.  It's an idea
which would be easier to accept if the first building were small and
intended for storage or animal housing.  (The Nader Khalil concept)
 http://forests.org/ric/good_wood/adobe_su.htm

If you are uncomfortable with the idea of a dome or vault house, the next
lowest cost roof used in conjunction with CEB or ceramic walls would be
ferrocement "channels" long enough to bridge across opposite walls plus a
desired three or foot overhang on each end.  Deriving from earlier
half-cylinder designs in South America which were fabricated over
screeded-contour earth molds, the more sophisticated ferrocement "channels"
employed in India are made by prefabbed molds on vibrating tables.  The
finished channels are laid adjacent to each other as a roof, the adjacent
lips covered with smaller inverted channels as clamps and seal against rain.
For suitable, low-cost insulation, pumicecrete, perlitecrete, or foamed and
surface-sealed concrete would be poured in the channels.  Foamed concrete
runs like water unless it contains a thixotropic agent.  Pumicecrete is
easier to handle in this respect.
http://www.ecouncil.ac.cr/devalt/livelihoods/buildingtechnologies.htm


----------------------------------------------------------------------------
----


Home Energy Magazine Online May/June 1999

----------------------------------------------------------------------------
----
Earth as a building material can be great for both builders and
homeowners--it offers low material costs and low transportation costs,
especially for earth dug directly from the site, and high thermal mass,
which can mean huge savings in energy.
----------------------------------------------------------------------------
----

Embodied Costs--The Real Price We Pay
Embodied cost is the complete life cycle cost of gathering, manufacturing,
transporting, assembling, and even recycling building materials (see
"Reducing the Embodied Energy of Buildings," HE Jan/Feb '95, p. 19). As long
as the materials are gathered locally, earthen structures of all kinds are
real winners in terms of embodied costs. In 1976, the Energy Research Group,
University of Illinois at Chicago, and architects Richard G. Stein and
Associates did a complete study of building materials and the embodied
energy that each represented. They found that earth's construction methods
gave it definite advantages in terms of resource consumption. Because adobe
is primarily soil, the energy costs of gathering and manufacturing are very
low, and if it is made from soil on site, the energy cost of transport is
also negligible.


Water is the enemy of earthen construction. This water damage was caused by
water leaking around old exterior flashing. It has leaked earth into the
interoir plaster, causing stains and making the plaster peel off.
Print Resources
Easton, David The Rammed Earth House. White River Junction, Vermont: Chelsea
Green Publishing, 1996.
McHenry, Paul Graham, Adobe and Rammed Earth Buildings. Tucson: University
of Arizona Press, 1984.

Internet Resources
* Rammed Earth Works
http://www.rammedearthworks.com
* Cast Earth
http://www.castearth.com

* New Mexico Energy Conservation and Management Division
http://intertech.albuquerque.nm.us/ecmd/html/
Publications/Adobe/archives/Adobe_TOC.htm

* U.S. Department of Energy
http://www.eren.doe.gov/EE/strawhouse/

* The Earth Building Foundation
www.earthbuilding.com



To manufacture pressed adobe block, workers dump earth into a hydraulic
adobe press. A large screen at the top sifts out rocks.

The dirt drops into the pressing machine and is hydraulically compressed by
almost half. The machine can produce up to 900 blocks per hour.

The blocks drop from the machine onto a conveyor, ready for a quick cleaning
and immediate stacking on pallets.

A Cast Earth home under construction, with some walls in the curing phase
and forms set up to pour new walls.

This Cast Earth home features a passive solar design, propane and wood heat,
and an evaporative air conditioner. The walls took just two days to pour and
cure. Note the wall's stair pattern, an indication of the building process.

The walls of this Cast Earth house and garage show the sandpainting effect
of the building process, as well as an extensive roof overhang that protects
the walls from water damage.
It takes a long time for even the hottest summer sun to warm up a heavy
earthen structure. That's one reason that earth has been a popular building
material in hot climates for many centuries and is still common in the
sizzling Southwest where I live. Earth is one of many alternative materials
that can be used in place of residential stick building. Due to its high
thermal mass, in climates that demand lots of cooling energy and have cool
nighttime temperatures, nothing works like earth.
Pros and Cons of Earth Building
Earth is a sustainable material, meaning that it has little impact on the
environment and that building with it expends little or none of the earth's
finite resources, such as fossil fuels. It also has low embodied costs--the
costs to individuals and society together of creating, storing,
distributing, using, and disposing of a given material (see "Embodied
Costs--The Real Price We Pay"). And earthen construction has passed the test
of time--until recently, earth-building technology changed very little from
the mud brick homes that were first built during the Neolithic period, back
in 7100 bc.
Earth building does pose some problems. Earthen walls don't span open spaces
or window and door openings very well, so they tend to crack near windows
and doors that have inadequate metal or wood lintels. If the roof fails,
moisture that seeps in can quickly erode the walls. Also, most earthen
materials are unsuitable for homes of more than two stories because in order
to carry the load of the upper walls, the lower walls would need to be
thicker than is typically practical to build. Furthermore, labor costs for a
two-story adobe home would be very high indeed.

Turn Off Your Air Conditioner

In hot, dry climates, the high thermal mass of earth-built homes can render
them substantially more energy-efficient than stick-built homes, thanks to
the flywheel effect of walls with high thermal mass (see "Mass Walls Mean
Thermal Comfort"). A recent study by Oak Ridge National Laboratory (ORNL)
found that the thermal mass benefit of high-mass walls is a function of the
wall's composition and the climatic conditions where it is built. For
example, in a hot, dry climate such as that in Phoenix, the energy demand of
a one-story house with high-mass walls is equivalent to the energy demand of
a similar wood-frame house made with R-25 light-weight walls. (More
information on the ORNL research will appear in the next issue of Home
Energy.)

When I don't use supplemental heating or cooling, the indoor temperature of
my adobe house in Tucson, Arizona, seldom rises above 85°F in the summer or
falls below 61°F in the winter--this in a climate with roughly 22 freezing
nights a year and frequent summer temperatures above 105°F. Tucson has 2,000
annual heating degree days and 3,000 annual cooling degree days.

I only run the air conditioning during July, August, and part of
September--the Tucson "monsoon" season. Otherwise, on most mornings, when
the desert air temperature is coolest, I simply close all the windows and
doors. Because it takes as long as 14 hours for the outdoor heat to pass all
of the way through the adobe block and heat the indoor air, night has fallen
before it gets hot indoors.

The humidity of the rainy season changes the equation and forces me to turn
the air conditioning on. Humidity lessens the differential between daytime
highs and lows, so drawing in night air no longer serves the same purpose.
After mid-June, the days are their longest, meaning that the sun is heating
the block longer and there are fewer night hours and higher night
temperatures. That means the adobe block hasn't enough time to give up the
heat gained during the day before it is daylight again. Nights also don't
get as cool (somewhere in the 70s). However, running the air conditioning at
night cools the house and serves the same effect as opening the windows. I
usually turn off the air conditioning in the morning and let the house coast
with its doors and windows closed until nightfall.

Thermal intertia is also at work in the winter, when fewer daylight hours
mean the sun simply doesn't shine long enough to warm the adobe block. This
means the house is cold for a much longer portion of the day than it is
warm. I have often been surprised to go outside and find it warmer outdoors
than inside. Forced air heat, which merely blows warm air around, isn't as
effective in a high-mass house as radiant heat, which physically radiates
warmth to people. Radiant floor heating warms the feet, the person, and
eventually the adobe. It make take longer to get the walls warm, but once
they are warm, they stay that way.

Thoughtful and selective insulation can efficiently modulate the thermal
properties of earthen homes. Although an external thermal barrier would
eliminate the earthen walls' role as solar heat collectors, that same
insulation placed within the walls acts as a heat sink for the home's
interior volumes. Adding insulation within north and east walls would be
useful in a very cold climate, while insulating within a west wall would be
advantageous in a hot climate.

Water--Earth's Enemy

Water is the enemy of all earthen construction. Water wicking up from the
ground erodes the bases of earthen walls, causing them to crumble and fall
away. Water from leaky roofs gets trapped in an earthen wall and oozes
mud-laden water onto the ceiling; if the problem is not fixed, it will cause
the plaster to pop off.

The degenerative effects of water can cause some earthen walls to simply
melt, although it may take a long time. Vertical surfaces exposed to as much
as 25 inches of rain per year will erode approximately 1 inch in 20 years.
Horizontal surfaces like the top of a wall, on the other hand, can erode as
much as 2 to 3 inches in a single year. Therfore, earthen homes must be
carefully stuccoed or sealed. Most earthen walls are stuccoed, but if there
is a deep roof overhang, clear wall sealer may be sufficient. How well an
earth-built home stands up to water depends on how well it is protected by
roofing and stucco or sealing, but also on how it was constructed and
whether it contains stabilizers.

New Technologies Come to Market

Thermal comfort isn't the only draw of thick earthen walls. They also have
an aesthetic appeal that is driving strong customer demand. Luxury homes
lead this market; in New Mexico, half of all new homes selling for more than
$300,000 are some form of earthen construction. Most of these are adobe, but
a growing number of them are built using new earthen technologies.

The most significant structural innovation in earthen construction was the
introduction in the 1930s of concrete foundations to protect the structure
from water. Concrete overhead bond beams to increase structural integrity
were another important change. More recently, various additives for
strengthening the bricks and increasing water resistance have been
incorporated into adobe mixtures. New construction methods and a revival of
older building methods are also being used.

Today, several types of earth construction compete with traditional adobe:
semistabilized and fully stabilized adobe, pressed adobe block, rammed
earth, Cast Earth, and Pneumatically Impacted Stabilized Earth (PISE). See
"PISE--Thermal Comfort Made Practical" for more detail on this last process.

Adobe
The word "adobe" refers variously to earthen blocks or bricks, to the
mixtures used to form them, to a type of mud plaster, and to the entire
building. New Mexico is the largest domestic producer and user of adobe. The
state is home to more than 59,000 adobe dwellings, one-third of all adobe
homes in the United States.
Most older, traditional adobe homes were built with earth excavated from the
site. The resulting hole became the basement, so these homes have basements
only as large as the volume of earth needed to build the walls. Then, as
now, typical adobe bricks measured 4 inches x 10 inches x 14 inches and
weighed approximately 30 lb.

Earth for modern adobe homes is typically quarried from commercial sites
where the soil content is known, and the bricks are made at adobe brick
factories. Adobe walls are typically 10 inches or 14 inches thick. Walls
taller than 6 to 8 feet high are thicker at the bottom than at the top, to
better support the load.

The kinds of adobe available today include traditional, semistabilized, and
stabilized adobe. (Stabilizers are additives that make the adobe stronger
and more water resistant.) Machine-pressed adobe block, often simply called
pressed block, is another type of adobe that is gaining popularity in the
Southwest. Such variations were developed in an effort to ward off the
destructive effects of water. More unusual variations of traditional adobe
include New Mexican terrones (cut-sod brick) and quemados (burnt adobe), but
these are not used very often. According to New Mexico State records,
semistabilized adobe is the most common variant currently in use today;
before 1970, most homes were the traditional untreated adobe.

Traditional Adobe

Traditional adobe bricks are found mostly in older homes. These untreated
bricks are made out of soil and straw. The sandy alkaline silt and clay
soils of the Southwest are much prized for adobe. The straw adds strength
and prevents cracking.

In constructing these bricks, the adobe makers moisten the mixture of straw
and soil to make a thick goop, then slap the goop into a mold, often a
simple, four-sided wooden mold. The adobe may stay in the mold anywhere from
two or three minutes to three or four hours to several days, depending on
weather conditions and on how square the bricks are meant to be. (Bricks
that have set for only a few minutes tend to slump or bulge out at the edges
and are not always square.) Then they knock the brick free of the mold and
let it dry out and cure in the sun for up to 30 days.

If the walls are dry and water is kept from wicking up into the building
from the earth, an adobe building can easily last 100 or more years.
Maintenance is important, though, since moisture can get in through cracks.
My own house is 62 years old and is in fine shape. Over the years there has
been minimal cracking in the plaster that covers the inside walls and the
stucco that covers the outside walls. The house does have one advantage in
that it sits on a concrete foundation.

Semistabilized Adobe

Semistabilized adobe brick was developed in New Mexico. Previously,
throughout the Southwest, sap from agave or prickly pear, straw, and manure
were among the additives used to stabilize adobe. Today, stabilized adobe is
made of plain earth mixed with a stabilizer that classifies the brick as
water resistant.

Liquid asphalt emulsion stabilizer, 3%-5 % by weight, is the most popular
additive because it is easy and inexpensive to use (it is a byproduct of the
road building industry). Portland cement, 5%-10% by weight, is also an
excellent additive, one that can be added to the dry earth and mixed in the
same way as concrete. The Portland cement augments the structural integrity
of the brick, so that the finished product is less crumbly than traditional
adobe.

Fully Stabilized Adobe

Fully stabilized adobe contains enough asphalt emulsion or Portland cement
to limit the brick's seven-day water absorption to less than 4% of its dry
weight. This amounts to about twice as much stabilizer as is used in
semistabilized adobe--6 to 12% by weight of the dry mixture. Because they
are so well protected, these bricks will last longer under exposure to the
elements (although they should also be sealed).

In 1994, 79% of the adobe bricks manufactured in New Mexico were
semistabilized; 21% were the traditional untreated adobes. Fully stabilized
bricks accounted for roughly 1% of the state's adobe production and were
available only on special order. Fully stabilized adobe is more expensive
than the other types and looks much more like concrete than like adobe.

Pressed Adobe Block

Pressed adobe block is the latest improvement to adobe. There are two kinds
of pressed adobe block: natural and semistabilized. Semistabilized adobe
pressed block contains 5% by weight Portland cement. Both types of pressed
adobe block are tougher than and less crumbly than other types of adobe.

The molds used for pressed adobe block are almost twice as deep as the molds
used for other types of adobe. Rather than simply curing the molded blocks
in the sun, the manufacturer uses a hydraulic press to set the mud under
extreme pressure. When the press goes to work, 4,000 lb per square inch
(psi) of pressure quickly compresses the blocks to the traditional 4-inch
thickness. Rather than the traditional 30 lb, each pressed adobe block
weighs a hefty 40 lb. As for tensile strength (modulus of rupture), it takes
100 psi of pressure to break pressed adobe block--double the uniform
building code requirement of 50 psi.

According to Keith Guffey of Tucson's Pascua Yaqui Adobe Company, pressed
adobe block has been proven by the manufacturers to be stronger than other
types of adobe. Other types of adobe, Guffey says, are strength rated at
400-600 psi, meaning that they can handle roof loads of that weight. Pressed
adobe block is strength rated at 1,000-2,000 psi.