BRICKS - Oolitic Middle School

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Oolitic Middle SchoolIndustrial Technology

The Story of Bricks

INTRODUCTION|WINNING|PREPARATION|MOLDING|DRYING| FIRING|MODERN BRICKS|SUMMARY

Words to know:

adobe, architecture, cavity, clinker, compression, course, cycle, die, exterior, extrusion, firing,green, interior, kiln, laminated, manual, oxide, porosity, pug mill, vitrify

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Introduction

It has been said that the study of bricks is the study of civilization.

Bricks made of mud and straw have been used for thousands of years.

Some bricks over 10,000 years old have been discovered. One of the

first building materials created by man, bricks are still a highly desired

choice to this day. Some of the newest homes and modern buildings

use bricks in their construction. The simple brick has maintained its
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reputation as a superior building product longer than perhaps any

other product in the modern world.

Plain mud bricks like the ones pictured on the left are called

'adobe' or sometimes 'slump bricks.' Examples of adobe bricks have

survived throughout history and are found

in many ancient buildings. Adobe was

used in the ziggurat temples ofMesopotamia and by the emperors of

ancient Rome. Since trees were scarce in

the Old Southwest, the American Indians

and the pioneer settlers alike chose adobe brick as the logical material

for buildings. Adobe bricks are still used in certain parts of the world

today.


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The cliff dwellings of Mesa Verde, Colorado

were built with adobe bricks around 1200 A.D.

Adobe bricks are made from a mixture of mud and small pieces of

straw or reeds. The bricks are formed by hand and left in the sun to

dry. But there is a problem with plain mud bricks. Over time, rain

water will dissolve them and cause them to crumble and break apart.


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Early brick makers eventually learned that if they would "burn" the

bricks by baking them in a very hot oven called a kiln, the bricks

would become very hard and durable.

The basic brick making process has survived for thousands of

years. To better understand the complete story, let's take a look back

into history and discover how the brick making process evolved into

the modern brick making industry of today.

There are five basic steps to making bricks.

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1. MINING. The first step is called mining or "winning" the clay.
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The original color of clay does little to indicate the color of thefinished brick. The color of a finished brick is generallydetermined by how much iron mineral is in the clay. Clay with a

high iron content will produce a deep red brick after firing (Seestep 5). Clay with less iron produces a buff or light browncolored brick.

The early brick makers relied on their own experience whenthey chose their clay. They chose it primarily by it's color andtexture. They didn't have the use of sophisticated laboratories toanalyze the clay back then. Because the steam shovel was not

invented until 1879, early brick makers had to dig for the claywith hand shovels. They obviously wanted to find their clay justunder the topsoil in order to minimize much of the harddigging.

The digging was usually done in the autumn. That way, theclay could be left exposed to

the freeze-thaw cycles of thecoming winter. A cycle is aseries of events that happenover and over again. Thefreezing and thawing over andover again would help breakdown the clay. That made theclay softer and easier to work


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by hand in the Spring.

The winter exposure not only made the clay soft but alsoremoved unwanted oxides. Oxides are minerals that havecombined with oxygen and are considered undesirableimpurities in brick making.

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2. PREPARATION. The second stepis preparation of the clay

By spring the clay was suitable tobe worked by hand. It was sometimes ground into a powder andsifted through a screen to remove stones. Sometimes the claywas placed into a soaking pit where it was mixed with water toobtain the proper consistency for molding.

A horse driven pugmill. This was agreat improvementover doing thisprocess by handsand feet.

Next, theclay was kneaded with the hands and feet to mix all theelements together. This step was called tempering orpuggingand was the hardest work of all. In the mid-1800's horse drivenpug mills (above) were invented to make this task easier. Pugmills are still used today, but of course they are now powered by


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huge electric motors instead of horses.

The clay was then removed from the soaking pit or pug millby a temperer who carried it to the molding table to begin thenext step in the process.

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3. MOLDING. The third step is molding.

The assistant brick molder was called the clot molder. Thatjob was to prepare a lump of clay (a clot) and give it to the brickmolder.

The brick molder was the key to the operation and the head

of the team. He or she would stand and work at the moldingtable for twelve to fourteen hours a day. With the help of theassistants, a brick molder could make 3,500 to 5,000 bricks in aday. They would take the clot of clay, roll it in sand and "dash" it(toss it forcefully) into a mold. A mold is a wooden frame that isthe shape of a brick. The clay was then pressed into the moldwith the hands. The excess clay was scraped from the top of

the mold with a flat stick called a strike that had been soaking inwater. This excess clay was returned to the clot molder to bereformed into later bricks.


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A brick molding table A single cavity wooden brickmold

Single, double, four, or six cavity brick molds were used. Acavity is the hollow area inside the mold where the wet clay isplaced to form the shape of the brick. A single cavity brick moldmade one brick at a time, a double cavity mold made two bricksat a time, and so on. Making one brick at a time had anadvantage since even a child could carry a single brick to thedrying area. Beech wood was the preferred material forconstructing the mold because it was believed that the claywould not stick to it. The top of the mold was often laminated(covered by a thin layer) with iron to prevent wear. The moldwas also coated each time with sand so the bricks would slideout easily. These types of bricks are referred to as "sand struck

bricks."

The next person on the team was called the off-bearer. Theoff-bearer's job was to move the filled mold from the moldingtable to the drying area using either a pallet or a wheelbarrow.There it would be placed on a level bed of sand. The off-bearerwould remove the brick from the mold, stack the brick to dry,


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then return the empty mold to the brick molding table. At the

molding table he or she would wet the mold and coat it againwith sand. It was now ready for the brick molder to form thenext brick.

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4. DRYING. The fourth step is drying.


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Bricks being wheeled to the hackstead and stacked for drying.Notice the color of the bricks at this stage.

The bricks were left stacked in the drying area for a fewdays. After about two days they were turned over. This wasdone to facilitate uniform drying and to prevent warping. Duringthis time tools called dressers or clappers were used tostraighten any crooked bricks and to obtain a smooth surface.

After about four days in dry, hot weather the bricks were


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Stacking and firing the kiln was part of the"art" of brickmaking. Green bricks were usedto construct the kiln shown above. The holesin the walls are the fire holes. The greenbricks were then stacked inside, about afinger's width apart so the heat would flowbetween them easily.

After the structure was daubed and sealedwith clay, wood or coal was placed in the fireholes, and the fires were lit. The fires werekept low for the first 24-48 hours until thebricks were completely dry. When the steamfrom the bricks cleared, the intensity of thefire was increased.

The fires burned for about six days day andnight. The brick makers remained on siteduring the entire burn period, getting littlesleep and keeping the fires burning. Near theend of the burn, the kiln reached atemperature of approximately 1,850 degreesFahrenheit.

Even after drying for more than two weeks in the air, thegreen bricks still contained 9-15% water. For this reason thefires were kept low for the first 24-48 hours while the brickscontinued to dry. During this time steam would rise from the top

of the kiln in huge white clouds. They called this steam "watersmoke."


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When the steam gases finally cleared it was the signal to increase

the intensity of the fires. If this was done too early, steam wouldform inside the bricks and cause them to explode. The brick shown

below on an old school house in Leesville, Indiana is an example of

this condition. This brick was fired too green and the internal gasses

caused it to burst open.

Intense fires were maintained in the fire holes around the

clock for about a week. It took that long to reach the requiredtemperature of around 1,850 degrees F.

Reaching the correct temperature was very important.When a brick reaches the correct temperature it begins to'vitrify.' Vitrification happens when sand and other materials inclay melt and fuse together. This changes the clay into a glass-

like material.

Properly fired bricks are very strong in compressionstrength. Compression is the squeezing force on a material. Inthe case of bricks, most of the compression force comes fromtheir own weight on top of each other. Bricks that do not get hotenough during firing are weak in compression strength and willcrumble under load. Bricks that become too hot will become


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too glass-like and brittle. The trick for the early brick maker was

to get them just right. The correct temperature was just at thepoint when the vitrification process began.

Since thermometers were not available in those days, thebrick maker had to rely on his knowledge and experience toguess when the bricks were done. At that time the fire was putout, the fireholes of the kiln were bricked over, thus ending thefiring process. It then took more than a week for the kiln to cool

down sufficiently to remove the bricks.

Medora Brick PlantA 50-man workforce once produced 54,000 handmade bricks a day at the

Medora Brick Plant in nearby Jackson County, Indiana. The plant opened in 1906.The round "beehive" shaped buildings in the picture are nine of the twelve

kilns that were used. The low tin-roofed buildings in the center of the picture are thehack-steads.

With its aging brick making technology, the old plant became unable to competewith more modern plants. The Medora Brick Plant closed on January 31,1992. Almost all brick that was used in this area before 1992 came from this brickplant. When cool,


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the kiln was disassembled and the sorting process begun. If

green bricks had been used to make the kiln, those bricks fromthe outermost walls were saved to be fired again in the nextkiln.

Some bricks which were closest to the fire received a naturalwood ash glaze from the sand that fell into the fires, becamevaporized, and deposited on the bricks. These bricks wereused in the interior(inside) courses of the walls because of

their attractive, slick and shiny appearance. A course is onerow of laid bricks.

Bricks that were severely over-burned,cracked, or warped were called 'clinkers'

and were occasionally used for garden

walls or garden paths. They were

probably called clinkers because of theclinking sound they made when they were

struck together. They were too glassy and

much too brittle to be used in buildings. Those that were only slightly under-fired had a salmon color

and early brick layers knew that the porosity (tiny air holes) inthese bricks would help to insulate a structure. These bricks

were placed on the innermost courses of a wall. This is anexample of a salmon colored brick.

Finally, the best bricks were chosen for the exterior(outside)walls of buildings because they were the strongest and mostdurable.
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Clay can now be transportedeasily from the mining site topermanent brick plants. There,

sophisticated testing labs, pugmills, temperature controlledkilns, and robotic equipment areused to transform it into hundredsof styles and textures of brickproducts. The making of bricksis no longer a guessing game

dependent upon the knowledgeand experience of only a fewpeople.

Modern high output brick factories have replaced the handmolding process with a much faster method of forming bricksfrom clay. Today's factories use what is referred to as theextrusion process. A large machine called an extruder forces


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a soft clay mixture through a small opening called a die. In this

case the die is a block of steel with an opening the size andshape of a brick. This forms a long continuous rectangle of claywhich can then be cut into individual bricks.

The extrusion process can be illustrated by the cookie pressshown below. Soft cookie dough is extruded through one of thedies shown on the left to form the desired shape of cookie. Thelong 'extrusion' of dough is then cut off into individual cookie

sections.

A cookie extrusion press A brick extrusion press The brickextruder being operated by the woman above right works on thesame principle. The long extrusion is first cut into about 6-footlong sections called slugs. The slug next passes through a rowof wires that slices it into individual brick sections, creating

several bricks at a time. This process is obviously much fasterthan the ancient method of molding bricks one by one by hand.

The extrusion process is used to form shapes in othermaterials as well. Aluminum extrusions are quite common.


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Aluminum is heated to make it soft so it can be extruded

through a die. Some familiar uses for aluminum extrusions arein residential storm doors and storm windows. Those arealuminum extrusions around the chalkboard in our classroom.

The Krispy-Kreme Donut Company uses the extrusionprocess to make their popular donuts. They would be unable tokeep up with the huge demandotherwise. Cutting donuts from a flat

sheet of dough as most companiesdo is much too slow. All of theKrispy-Kreme stores together canextrude a stack of donuts as high asthe Empire State Building in only 22seconds.

Can you think of other products that are extruded?

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Summary

Bricks have been around since man first began buildingstructures. Some say architecture, the art and science ofdesigning and constructing buildings, began when the first twobricks were laid together well.
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A robot handlesbricks in amodern brickplant.

Thehistory of the brick industry is a good example of the benefits ofmass production. Modern brick making uses at least somevariation of every one of the five original steps we havediscussed. Today, much of the difficult, manual (hand)labor is

performed by high-tech machinery and computer controlledrobots. Laboratories ensure consistent clay mixtures.Temperature and atmospheric controlled kilns produce uniform,high quality bricks in hundreds of varieties, shapes, and sizes.


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The warm solid feeling of a brick house is greatly preferred bya wide variety of home builders. Ask the Three Little Pigs!

Bricks are attractive and relatively inexpensive products withgood mechanical properties. The natural resource (clay) isplentiful and readily available. These are necessary qualities ofany good building material.

Nevertheless, bricks are essentially just burnt clay. . . and,they have been around for thousands of years. Amazingly,they continue to serve as the backdrop of the modern age.


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We have all been taught since childhood to follow the yellowbrick road . . . to follow our dreams into the future. When wedo, we will no doubt discover that the age-old brick is still with

us when we get there. When it comes to bricks, perhapsmodern isn't as modern as we think it is.

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Copyright (c) 2005-07, Harley D. Brown, Oolitic Middle School, Oolitic, Indiana
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BRICKS - Oolitic Middle School

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