EARTH CONSTRUCTION

Rammed earth is essentially manmade sedimentary rock. Rather than

being compressed for thousands of years under deep layers of soil, it is

formed in minutes by mechanically compacting properly prepared dirt. The

compaction may be done manually with a hammer-like device,

mechanically with a lever-operated brick-making press, or pneumatically

with an air-driven tamping tool. Dynamic compaction using manual or

power tampers not only compresses the soil, but it also vibrates the

individual dirt particles, shifting them into the most tightly packed

arrangement possible. When finished, rammed earth is about as strong as

concrete.

Houses built of rammed earth have several advantages over wood-frame

construction. The walls are fireproof, rot resistant, and impervious to

termites. The solid, 18-24 in (45.72-60.96 cm) thick walls are nearly

soundproof. The massive walls help maintain a comfortable temperature

within the house, damping temperature swings that normally occur on hot

summer days or cold winter nights. When designed and oriented to take the

best advantage of solar energy, a rammed earth house can be comfortable

with 80% less energy consumption than a wood-frame house. On the other

hand, initial construction is about 5% more expensive than wood-frame

construction because it is very labor intensive.

History

Humankind has used the earth itself to build homes and other structures

for thousands of years. Jericho, the earliest city recorded in history, was

built of earth. Temples, mosques, and churches were built of mud bricks

and rammed earth throughout the ancient Middle East. Egyptian pharaohs

ruled cities constructed of rammed earth. In the Far East, the technique

was used not just for houses, but even for building ancient forerunners of

the Great Wall of China. Romans and Phoenicians brought the technology

to Europe, where it was used for more than 2,000 years.

In the United States, rammed earth construction enjoyed a period of

popularity from 1780 until about 1850, when mass-produced fired bricks

and sawed lumber became readily available. Houses could be built more

quickly and easily with bricks and lumber, which were considered more

modern and elegant materials than dirt. The supply shortages experienced

after World War I and during the Great Depression brought rammed earth

construction back into favor for two decades. Frank Lloyd Wright designed

houses to be made of rammed earth.

When World War II ended, the country faced a large demand for housing,

and wartime factories turned to manufacturing building materials that

could be used for quicker types of construction. Rammed earth was

brushed aside until it was repopularized during the environmentally

conscious 1970s. A modified version of the technique, invented by Michael

Reynolds, uses building blocks of discarded automobile tires rammed full of

earth. These houses not only keep used tires out of landfills, but they can be

built by inexperienced, first-time builders. When a homeowner uses the

unpaid labor of himself, relatives, and friends, and when he can obtain

many of the building materials for free, the construction cost can be held to

less than half that of a wood-frame house.

For thousands of years, rammed earth construction was taught personally

by one generation of builders to the next. In early twentieth-

century America, such a network of experienced builders did not exist. The

U.S. Department of Agriculture developed and published a manual

titled Rammed Earth Walls for Buildings that showed people how to build

their own homes. Research projects designed to improve the methods and

quality of rammed earth construction were reported in academic journals,

and more than 100 articles on rammed earth appeared in trade and popular

magazines from 1926 to 1950.

Several more recent innovations increase the speed and ease of

construction and enhance the structural integrity of the final product. For

example, pneumatic tampers can be used to compact soil much more

quickly than the traditional manual method. Easy-to-assemble forms allow

walls to be built as solid panels rather than building them up as successive

layers a foot or two at a time. Using time-honored manual methods, a four-

person crew can erect 40-50 sq ft (12.19-15.24 sq m) of rammed earth wall

per day; with power tools, the same crew can construct 300 sq ft (91.44 sq

m) per day. David Easton, founder of Rammed Earth Works, has developed

several earthquake-resistant designs to reinforce and structurally integrate

the walls; the choice of design alternative depends on several

considerations, including the distance to the nearest seismic fault.

Raw Materials

As the name implies, the primary material used in rammed earth

construction is the earth itself. There are five basic types of soil (gravel,

sand, silt, clay, and organic), and the dirt in a given location is generally

some combination of all or most of these types. Historically, the longest

lasting rammed earth walls were made of soil that was 70% sand and 30%

clay. The soil from a new building site is tested to determine its suitability.

Organic material must be removed from the soil and, if necessary, a

different type of soil can be trucked in and mixed with the existing dirt to

create a blend that will work. Cement may be added to the soil to increase

both its strength and its resistance to moisture—usually at about one-fourth

the ratio that would be used to make concrete.

Steel reinforcing bars are placed in the foundations and sometimes in the

walls. Plywood is used to make the removable forms for standard rammed

earth construction. Sheets of three-quarter-inch (1.9 cm) plywood are thick

enough. High-density-overlay (HDO) panels, which have a thin, plastic

coating on one side, work especially well because they release more easily

from the wall after construction. This not only leaves a clean finish on the

just-completed wall, but it leaves the form boards in good condition to be

used on future projects.

Rammed-earth tire construction uses discarded automobile tires,

aluminum cans, and cardboard in addition to compacted soil. About 1,000

tires are used to build the walls of a 2,000 sq ft (609.6 sq m) house.

Design

Rammed earth houses are custom designed to make the most energy-

efficient use of the site. They can be successfully designed for many climate

regions, including humid areas with cold winters. The size and placement of

windows is an important factor in taking advantage of solar heating in the

winter and cooling breezes in the summer. The house can be positioned to

take advantage of hills that offer protection from storms. Shade trees

or trellised vines offer relief from summer heat but admit warm sunlight in

winter.

The Manufacturing

Process

Rammed earth houses can be built in one of three basic ways. Individual,

rammed earth bricks can be formed and used with standard building

techniques; in fact, such bricks may be used to form the floors in a rammed

earth house built with other techniques. Standard rammed earth

construction involves erecting wood forms and compacting

Standard rammed earth construction involves erecting wood forms and

compacting the prepared soil into these molds, which are removed after the

walls are completed.

In the tire method, a row of used automobile tires is simply laid atop the

concrete footing, perhaps centered around steel reinforcing bars that

extend out of the footing. The tires are then filled with soil. About 1,000

tires are used to build the walls of a 2,000 sq ft 1609.6 sq m) house. the prepared soil into these molds, which are removed after the walls are completed. The rammed-earth tire method is a commonly used alternative. The descriptions that follow are overviews of the standard and tire methods.

Preparing the site

1 An inch or two (2.5-5 cm) of topsoil is removed from the building

site and stored so it can be replaced around the completed structure.

Organic matter such as weeds and roots are removed and may be

composted for use in post-construction landscaping. After the site is

cleared, the outline of the house is staked out. The soil is excavated to

a depth that guarantees a level surface; the excavation includes the

floor area of the building as well as a 3 ft (1 m) surrounding buffer

zone. A trench may be dug so that the walls will be anchored into the

ground to a depth below the winter freezing line.

Laying the foundation

2 The foundation, which is made of reinforced concrete, consists of a

footing that may be as narrow as the thickness of the wall or up to

three times that thickness, depending on the strength of the

underlying soil. The footing is extended above ground level to form a

short "stem wall" that will connect the rammed earth walls to the

footing. Depending on the architectural design, a slab floor may also

be poured.

Analyzing the soil

3 A variety of tests are conducted to determine the suitability of the

local soil for construction material. For example, a particle

determination test reveals the relative proportions of sand and silt in

the sample. A compaction test is performed by forming a ball of mud

and dropping it from a height of 3 ft (1 m); the degree to which the

ball disintegrates on impact reveals its usefulness for building. Other,

more precise, tests can be performed at a geotechnical laboratory. If

the native soil is unsuitable or inadequate for building, it can be

blended with or replaced by soil from another source. Soil may be

purchased from a quarry, or it might be available as refuse from a

nearby construction site, in which case it could be delivered free or at

a minimal cost.

Framing the walls

4 Traditionally, wood forms were used to build up walls 2 ft (0.6 m)

at a time. After the mold was filled with fully compacted soil, it would

be removed and reset to form the next section of wall. More efficient

methods now allow forms to be constructed for the entire height of

the wall (even more than one story). Horizontally, the framework

may form the complete length of wall, or it may form shorter panels

[e.g., 8 ft (2.44 m) long] separated by 6 in (15 cm) gaps that can be

filled with reinforced concrete for enhanced structural strength.

Framing is a major component of the construction process, in terms

of both importance and time; it usually takes less time to fill and

compact the soil within the forms than it does to set, align, and

remove the framework.

In the case of rammed-earth tire construction, wood forms are not

used. A row of used automobile tires is simply laid atop the concrete

footing, perhaps centered around steel reinforcing bars that extend

out of the footing. After each layer of tires has been filled and

compacted, another layer will be added, offset by half the tire

diameter from the layer below.

Tamping the soil

5 Traditional tampers are made of a heavy wooden block with a

handle extending upward through its center. A more compact version

can be made from a 4 in (10 cm) square steel plate welded to a section

of 1 in (2.5 cm) pipe. A 4-6 in (10-15 cm) layer of moistened soil is

placed inside the form, and a worker drops the tamper from a height

of 12-18 in (30-46 cm). In fact, most of the work is now done quickly

with pneumatic tampers, and manual devices are used only in tight

spaces around electrical boxes or plumbing pipes. After many

repetitions with the tamper over the entire surface of the layer, the

noise made by the impacting tamper changes from a dull thud to a

ringing sound. This happens when the soil has been compacted to

about half of its original volume. At this point, another layer of

prepared soil is added, and the tamping process is repeated. When

the tamping is finished, the wood forms are removed.

The tamping process is different when tires are used as the

framework. In this case, a sheet of cardboard is placed across the

bottom of the hole in the tire, and moistened soil is shoveled into the

tire. The dirt is packed by hand into the interior of the tire, and then

it is compacted by repeated blows with a sledge hammer. Using this

technique, about three wheelbarrow loads (350 lb or 158.9 kg) of soil

can be packed into each tire. Pounding the dirt causes the tire's walls

to bulge, interlocking the tire to the row below. As additional layers

are added and the wall becomes taller, scaffolding must be

constructed so workers have a place to stand while filling and

pounding the tires.

Finishing the walls

6 Interior faces of walls are often finished with plaster. If such a

coating is not applied, the wall should be treated with a clear,

penetrating sealant to prevent dust from sloughing off. Because stone

(even when manmade from rammed earth) is somewhat porous, it

may be necessary to apply sealant to weatherproof the exterior faces

of the walls in certain climate areas.

Rammed earth tire walls are finished by inserting aluminum cans

into gaps between the tires and filling remaining voids with adobe

(straw-reinforced mud). Earth is packed against the exterior face of

the wall, creating a flat surface that completely conceals the tires.

Wall interiors are finished with 2-4 in (5-10 cm) of plaster or stucco.

Byproducts/Waste

Rammed earth structures use natural resources efficiently. Those made of

packed tires even make productive use of some of society's trash. Because

the tires are sealed within 3 ft (0.9 m) thick walls, neither oxygen nor the

sun's ultraviolet rays can react with them. This means they cannot catch fire

and they do not release toxic chemicals. The structures qualify for better

fire ratings than wood-frame buildings, and they do not smell of rubber.

The Future

During the late 1700s, a French builder named Francois Cointeraux

founded a school in Paris to study and publicize rammed earth

construction, which he called pise' de terre (puddled clay of earth). Today,

David Easton has developed a new version of rammed earth construction

he calls PISE (Pneumatically Impacted Stabilized Earth). It involves

spraying the prepared soil under high pressure against a one-sided form.

This technique can produce 1,200 sq ft (365.76 sq m) of 18 in (45.72 cm)

thick wall per day, which is four times faster than a typical, four-person

crew can fill box-like forms and compact earth with power tampers.

Where to Learn More

Books

Easton, David. The Rammed Earth House. Chelsea Green Publishing

Company, 1996.

McHenry, Paul Graham. Adobe and Rammed Earth Buildings: Design and

Construction. University of Arizona Press, 1989.

Periodicals

"Rammed Earth Construction." Countryside & Small Stock

Journal, March/April 1992, pp. 32-33.

Other

"Rammed-Earth Tire Homes" February 9,

1997. http://monticello.avenue.gen.va.us/Community/Environment/Yello

wMtn/men .html (May 22,1997).

— Loretta Hall

Read more: http://www.madehow.com/Volume-3/Rammed-Earth-

Construction.html#ixzz39P9ZJTiQ

What is Cob?

Cob is earth used as a building material. Straw is mixed in with it to improve its

strength.

If your soil is too sandy, you add a little clay. If your soil has too much clay in it,

you add a little sand. If you are lucky, your earth may be just right. We call this

‘ready-mix’.

Can I Use the Soil from my Garden?

You don’t use any old soil. You discard the top soil, the stuff that gardeners

love. It is full of decomposed leaves and micro-organisms. You are after the soil

below that, the sub-soil, the inorganic material. Nobody wants that. But it is

exactly what you need. One man’s junk is another man’s treasure.

You need to dig up the earth to lay your foundations. Instead of dumping it,

you will turn that earth into the building that will sit on top of those

foundations. That’s pretty amazing.

Back to Top

How do I Mix in the Straw?

You have your supply of sub-soil with the right balance of sand and clay. Now it

is time to mix in your straw. You can do this by dancing on top of it, by letting

livestock trample on it, or by mixing it using various basic machines. Using

livestock to trample the cob overnight is a very ancient (and sensible) method.

Animal dung can improve cob’s workability, but be careful of this approach if

you live in a country with dung beetles; I saw one destroy a mud-dung floor in

Oregon. It looked like a tiny mole had crisscrossed over the entire surface

(being cob, though, it was very easily repaired).

Back to Top

What Happens Next?

You build.

Back to Top

So Cob is Environmentally-Friendly?

From an environmentally-friendly point of view, it does not get much better.

You source your raw material yourself, right where you want to build. No tree

is cut down, no rock is quarried, no metal is mined, no oil is extracted.

Your raw material does not require any melting or heating at high

temperatures, or the addition of any chemicals or massive quantities of water,

to turn it into a building material.

There is no need for transport from the forest/quarry/mine/rig to the factory;

no transport from the factory to the builders’ providers; no transport from the

builders’ providers to your site.

Cob is not toxic. It will not harm your health if you live a lifetime within earthen

walls.

In generations to come, if your home is no longer occupied, cob will eventually

disintegrate back into the earth. It will leave no trace. That is a pretty special

quality in a building material and often all too rare. When checking the 'green-

ness' of a building material, you need to think about its whole life cycle - from

the cradle-to-the-grave. If you would like to read a bit more about this, please

click here.

Cob goes even one step further. It is perpetually re-usable. This is known as

cradle-to-cradle. When a material has finshed its first tour of duty, it can be

used a second time. In the case of cob, it can be used a third, fourth, fifth time.

By adding enough water to a cob wall, you can actually re-sculpt it. If you

knock a cob wall down (for an extension for example), you can simply add

water and use that original cob to build your new wall.

I visited a 150 year old Irish cob cottage in 2009. The wall had been severely

damaged due to the application of cement render in the 1950s. The owner had

the foresight to gather up and store the crumbling cob. The wall could be

rebuilt using the original material. Isn't that wonderful?

Back to Top

What Does it Cost?

It is free, except for the labour you put in. You do put in a lot of labour.

Be aware too, that you will need to roof your cob home, have built-in

furniture, etc. It is more time-consuming and trickier to add these elements to

a curved building. If you need to pay trades people to help you with these

aspects, it will be more expensive than if they were fitting out a rectilinear

house. There are tricks that we can teach you to minimise this kind of

expensive input. Check out our courses.

At the end of the day, your cob home should not cost any more than a

standard-built house. It is possible to build it cheaper than a standard house.

We certainly did. At the end though, you will not have a standard house. You

will have created something beautiful, sculptural, personal and enduring.

Back to Top

Can Anybody Build with Cob?

Anyone can build with cob, small children and grandparents alike. Personally, I

am nervous of power tools. There is no need for them when cobbing. When a

batch of cob is made, traditionally it is rolled into ‘loaves’. You don’t need

strength to carry it from A to B. You size the loaf, or cob, to your ability. Each

loaf gets worked into the monolith of cob below.

If working on a larger scale, you can pitchfork or shovel cob into place and

work it in with simple wooden tools. Whether working with small cobs, or

larger shovelfuls, this is building at a human scale (something which is absent

from so many contemporary buildings, with all of their components craned

into position).

Back to Top

Can I Form Organic Shapes with Cob?

Cob is sculptural. You can curve it. You can carve into it. You can add on to it. It

can be reworked at any stage in its life. Cob works really well in curves. A

curved cob wall is actually stronger than a straight one, as it becomes self-

buttressing; it supports itself. This opens up so many possibilities for a

completely individual building, full of personality and free from the 1.2m x 2.4

(4ft. x 8ft.) module dictated by so many modern building materials.

Curved or non-uniform rooms feel good. There is a theory that as humankind

evolved in nature, we can only be truly comfortable when we are in ‘natural’

environments. The box-shaped rooms that most people live in nowadays are,

in fact, alien to us. We are not meant to spend so much time around so many

straight lines. Modular, straight building components are the result of

mechanisation for mass production. They are driven by profit margins and

convenience, not by any regard for the health or well-being of the future

occupants of these buildings. A curved or randomly shaped room feels like it is

embracing you. There are no dead corners. There is a flow. It is a pleasure to

spend time there.

Back to Top

A Feast for All the Senses?

Architecture should be about all the senses. Too often, architecture is purely

visual. Cob buildings are extremly tactile. The first thing that people do when

they visit our house is carress it. They touch the walls, they follow the line of

the curves with their hands. Visitors are surprised at how much they want to

do it, but everbody does it, spontaneously and without exception.

The mass of earth and non-uniform shapes of cob also allow for wonderful,

gentle acoustics - that's the sense of hearing covered. Cob buildings do not

really smell - perhaps the slightest hint of earth - an outdoors, natural smell.

There is a definite absence of chemical smells. Cob buildings look good enough

to eat. Geophagy, or 'eating clay/dirt/earth', happens worldwide for cultural,

dietry and/or medicinal purposes. I wouldn't recommend it, but maybe cob

can really claim to satisfy all of the senses.

Back to Top

I Want to Get Back to a Sense of Craftmanship

Cob is labour intensive, but it is extremely satisfying. As there is a slow food

movement, so cob belongs to the slow build movement. Cob-builders are not

getting a consumer product instantly off the shelf. They are spending time,

crafting their building, taking great pride in their work. The building process

may take longer than usual, but the legacy will last for generations.

Back to Top

Are There Any Special Considerations Working with Cob?

Cob buildings are built as monoliths – huge, thick, solid walls. Traditionally they

were built approximately 600mm (2 ft.) wide, up to a storey-and-a-half or

more.

They need ‘a good hat and good boots’, large overhangs and stone or block

plinths to minimise the amount of rain reaching the cob walls. They need to be

finished with compatible materials, which will protect the cob but also allow it

to breathe.

If you maintain your cob building well, such as re-newing your external

limewash every few years, it will last for generations.

Back to Top

What About Insulation?

Cob does not have a "good" u-value. The current building regulations in Ireland

require that the maximum u-value for a wall should be 0.21 W/m²K. A 600mm

wide cob wall will only achieve values from approxiamtely 0.4 to 0.65 W/m²K,

pretty far off the mark. This implies that cob walls need to be heavily insulated

to achieve current standards of thermal comfort, but our experience begs to

differ.

The building regulations do not take into account cob’s excellent thermal mass

properties (the walls act like slow release storage heaters), its monolithic

nature (which has a effect on how heat passes through the wall), its thermal

inertia properties and the fact that the mass of earth in the walls is a huge

reservoir for water vapour (reducing humidity levels in a room, which allows

you to feel more comfortable at lower temperatures). These qualities need to

be investigated and measured further if cob is to be accepted as a viable

modern building material.

In our house, we compensated for cob’s alleged inadequate insulation

capability by super-insulating everything else – the floor, the roof and the two

coldest walls of our home (north and east – these are timber-frame, with

straw-bales for insulation and cobbed up the inside with 100mm (4”) of cob).

In the winter, our house is toasty with only a 10kW turf-and-wood-stove to

heat 130m² of floor area, as well as our hot water. We have no back-up heating

system (we have solar water panels for our summer hot water). I cannot feel

any difference between the rooms which are entirely surrounded by cob

compared with the rooms which are partially or totally super-insulated.

The problem of straight-forward compliance with the building regulations will

be an issue for anyone wanting to take on a cob building. If you want to read

more about this, please click here.

COB CONSTRUCTION

A building needs a strong foundation to rest upon. This is the first detail to consider when building any structure.

It should be a unified and stable base for your building to sit upon, and must also support the load of the building.

It was our goal during Week One of Aprovecho’s Sustainable Shelter Workshop Series (www.aprovecho.net) to

construct a stone foundation for the building we would be working on for the next 7 weeks.

Alan Ash, a master stone mason (thestonemason.com), was brought in to instruct and guide the foundation

building process. Alan has been working with stone for 30 years and had a huge wealth of knowledge and

experience to pass along to us throughout the week. Alan is a real character, and a joy to work with! He knows

how to get’er done! And as he’ll say, “Damn, I’m good!” He really IS damn good!

The foundation was done with mostly dry stacked stone (local Oregon basalt), and mortared on each pier with

lime mortar. A clay/lime mortar was used between the other stones that were above grade. With dry stone

masonry, gravity, friction, and the skill of the worker are what holds your stone work together.

I thought, rather than writing out big long paragraphs of what we did, here is a basic step-by-step process of what

we did to build our foundation. If you have questions about any steps in the process, please leave a comment

below.

1.SitePreparation

Clear a level pad for your building. Make it at least 3 feet bigger than the size of your building on all

sides so that you have room to maneuver about the site.

Set up batter boards. These allow you to run string lines for the outside and inside of your foundation

trench. Always use a line level to level these strings.

Make sure that your foundation is “square” by using the Pythagorean theorem.

Dig your foundation trench down to the frost line (depends on where you are). Make the sides of your

trench vertical, square on the sides, and tamp down the bottom.

Determine your drainage point, and make the bottom of your trench slope down to where the water will

drain out. Standard good practice is to have it slope down ¼ inch per foot (1 inch per 4 feet). This is

pretty slight. Use either a transit or a water level to do this part. The Egyptians used water levels to level

the pyramids so don’t be turned off by this ancient tool. It works just as well as a transit for this job. Just

make sure that there are no bubbles in it.

2.RubbleTrenchandDrainagePipe

There are a couple different ways to create a rubble trench for your foundation. I have a more detailed guide in

my eBook“Build a Cob House: A Step-By-Step Guide.”

Here are the basics though:

Lay down a few inches of gravel on the bottom of your trench and tamp it down. Use drain-grade gravel.

Use landscaping fabric to cover the bottom and the sides of the rest of the trench surfaces. Leave

enough on top so that you can wrap it back over the top when you’re done.

You typically want to start your stone foundation or stem wall about 6” below grade. So measure down

from the top of your trench about 6”. This will be where your rubble trench ends.

Fill about 1/3 of your trench with drainage gravel again. Now filling over the top of your landscaping

fabric.

Lay in your perforated drainage pipe on top of this layer of gravel. Make sure that it is leading out to your

drainage point.

Fill in the rest of your trench with gravel and cover the drainage pipe, but leave an extra 2” free for now.

(Remember to keep 6” of space below grade to start your stem wall foundation too.) So leave about 8”

free of gravel at this point.

Cover the landscaping fabric over the top of the gravel, making a “burrito” of sorts. Cover this with

another 2” of drainage gravel all around.

Tamp your gravel inside the trench.

Begin your stone foundation or stem wall.

3.StoneLaying

Grade your stone – sort out the stones by size. The larger rocks will go on the bottom of your

foundation. Also pick out corner stones with a nice 90 degree angle, and mark these with a big X.

Set up your next set of tapered batter boards. You need to build these according to your structure. The

top surface of rock foundation walls should be NO LESS than 16 inches wide. The minimum height of a

stem wall above grade should also be 18 inches. Our batters moved in 2” per each foot upward in

height.

Lay your corner stones for the first layer and start from there.

Lay the exterior layer first. You will probably have one interior and exterior layer of stones for your

foundation.

Always lay your stones lengthwise into the wall! This is important in order for your foundation to last a

long time.

Lay your stones so that the “face” that you want is showing on the outside of your foundation wall. Try to

use faces that have a slight upward slope to them. This will help shape your wall nicely.

You want all of your stones to have contact. They all need to touch!

Insert “hearting” in between your large stones. This is a critical step! Hearting is just smaller stones or

gravel to help support the large stones and fill in the gaps. Use your “waste” rock for this. Try to insert

one bigger rock and then some smaller ones. When adding hearting, always lay it in from the inside of

the stone wall, and don’t put it in from the exterior of the wall. This prevents them from wedging out over

time. Also, don’t force the hearting in. You don’t want to disturb your large stones’ positions.

Lay the interior layer of stones now. Use the stones without a good shape or face for your inside layers

since these won’t be seen. As Alan Ash would tell us, “Just get the shittiest big rock!” The words of a

Master…(Note: This is not always his general rule of thumb though. He has reason for what he says.)

Insert more hearting to fill in all the gaps too.

For “static” stone laying, you will lay one layer of stones at a time. For each layer, lay a string line by

attaching it to two opposite tapered batter boards. This will help guide you up at the right slope as well.

Follow the 1 over 2 rule. Lay one stone to cover the break between the two stones below it. This is

called “breaking the joint.”

4.Mortaring

If you’re mortaring your stones together, lift up the stones and place them aside. Keep them in the same

direction so that you know how they should go back in place.

Lay your mortar down where your stone will sit.

Place your stones back in place on top of the mortar.

Re-insert your hearting, and add new hearting inside of the mortar if needed.

We used Natural Hydraulic Lime mortar on this structure. You can also use cement mortar if you

choose. NHL is best for mortaring stones underground as it sets in water. It is harder to come by than

cement mortar and costs a lot more though. If you’re on the East coast, you can get NHL and lime putty

through Virginia Lime Works.

This is a potentially good recipe for lime mortar: Use 3 parts sand to 1 part NHL. The amount of water

can vary, but it will be about ½ part water. We tested the sand that we were using for voids as well as

gradation and that’s how we came up with the 3-1 formula. Often it can be 2.5,1, or even less though.

A good recipe for a clay/lime mortar is: 6 parts sand, 1 & ½ parts sifted clay, ½ parts lime putty, and

about 1 part water. (Add the water and lime first.) This is mortar to only be used on the above grade part

of the wall.

That basically sums up what we did and how to build a stone foundation for your cob house or any other manner

of building you might be envisioning.

ADOBE CONSTRUCTION

In southwestern United States and Mexico (as well as other parts of the world), where there

are not many trees, people often build houses out of mud bricks called adobe. Adobe houses

are warm in the evening and cool in the daytime.

If a mud brick is warmed by the sun, how long will it continue to give off warmth once the

sun goes down?

Round huts made of bricks

Materials for making mud bricks:

Soil

Water

Bowl

Large mixing spoon

Straw, dry grass or pine needles

2 thermometers

One-pint milk carton

Clock

A sunny window

Pencil and paper

How to make mud bricks:

Gather some straw. If you do not have straw you can use dry grass, or dry pine needles.

Put the straw, soil from your yard, and water into a bowl and mix it well.

Open the top of the empty one-pint milk carton. Pour the mud mixture from the bowl into the

milk carton.

Make a hole in the mud by pushing a pencil halfway down in the middle of the opening.

Loosen the mud around the pencil by moving the pencil in a small circle, and then leave it in

the carton.

Place the milk carton in a sunny window and leave it there for several days to dry.

When the brick is firm and dry, take the pencil out of it and peel off the carton.

Leave your brick in a sunny window for one more hour. Then, put the brick on a table out of

the sunlight.

Put a thermometer into the hole of the brick. This will measure the temperature inside the

brick.

Lay another thermometer nearby on the table to measure the temperature of the air outside

the brick.

Wait a few minutes, and then read and write down the temperatures showing on the

thermometer inside and outside of the brick. (How long will it take before the thermometer

inside the brick is the same temperature as the one outside of it?)

Many people around the world use different materials to build their houses. What are some of

the advantages to using adobe bricks to build a house? What could be added to the mud mix

to make stronger bricks?

Adobe bricks are not used for building in places where there is a lot of rain, or where it is

cold. What would happen if adobe bricks froze and thawed a lot? What happens to adobe

bricks if they keep getting wet?