at Colonial Williamsburg, tourists can process the clay used for making bricks
at Colonial Williamsburg, tourists can process the clay used for making bricks
clay formed into bricks must dry before being assembled into a kiln and baked
Making brick is an ancient art. Some of the oldest discovered to date have been excavated at the town of Jericho in modern Turkey. Bricks there are 9,000 years old, dating back to 7,000 BCE.
Those bricks were made from mud and dried in the sun, similar to the construction of adobe houses. Bricks that were intentionally fired 5,000 years ago to metamorphose (vitrify) the clay and make it more waterproof have been found in China. However, the Native Americans in Virginia made only pottery. They heated clay in firepits fueled by wood and manufactured cooking vessels. They produced just earthenware. The Native Americans never fired clay at a high enough temperature (2,000°F) to make bricks.
Bricks are a human-made metamorphic rock. The raw material is clay, a sedimentary layer formed of particles that decomposed from feldspar and other bedrock minerals and washed downstream to an accumulation site. There is clay throughout the entire Coastal Plain, and it is common in stream valleys within all other physiographic provinces. There is no shortage of the raw material in the Piedmont or Coastal Plain of Virginia.
Clay particles are formed in the process of weathering (diagenesis) in which the molecules of feldspars and other minerals realign as heat and pressure changes. Hot hydrothermal fluids and cold groundwater both facilitate the transformation. Different forms of clay, such as kaolinite, illite and montmorillonite, are produced from different parent materials and under different conditions. Compression of clay and silt particles creates a mudstone. That shale, when metamorphosed, become slate.1
Clay for pottery and fired bricks contains no organic material or pebbles. For make adobe fir structures, about 30% of the material is clay. The majority is sand, glued together by the clay with 10-20% organic material (straw or animal hair) before the mixture is dried in the sun.
Construction with clay dried in the sun is far easier than converting the clay into bricks, and the first buildings at Jamestown were made from wattle and daub. Mud, whether dried first into adobe or just applied as wet mud to a framework of wooden "wattle" and then allowed to dry into "daub," is vulnerable to rain.
Virginia's first colonists built thatch roofs with wide overhangs to prevent water from eroding the exterior walls. Fired bricks are more suitable for permanent structures in Virginia's climate, with 40+ inches of rain per year.
To make a brick, organic material must be removed from the clay before it is heated; otherwise, plant fibers will burn away in the high temperature kiln. That will create gaps in the brick, or cause the brick to fall apart. To create waterproof bricks, topsoil is removed before clay is mined. All remaining organic material then is separated from the clay, before a brick is molded into shape.
Pebbles and stones also are removed. In a kiln, they will heat to a different temperature than the clay. That difference will crack a brick or cause gaps between clay and rock.
Making bricks is similar to making pottery. Pottery makers add a selected amount of sand or crushed shells to their clay as temper. The sand/shell particles have a different shape than clay particles. Adding a small amount of temper, mixed well into the clay, allows the clay to release moisture as it heats. Without a way for vaporized water to escape, the pottery would crack in the fire due to steam pressure.
Sand in clay is useful as a temper for brickmaking, through more than 30% sand can prevent the clay particles from fusing together. Though clay is common in the Piedmont and some of the Coastal Plain, successful brickmakers carefully chose the source of the clay they would use.
Bricks are made in a traditional way each year at Colonial Williamsburg. It is the last place in the United States to fire a large number of bricks with a wood-fired kiln or "clamp."
The mounds of mined clay are exposed to rain/snow over the winter. The freeze/thaw cycle helps to break up the clay particles, making it easier to process to the desired level of plasticity. Precipitation washes salts out of the clay, so the bricks in a building do not develop a white coating as they age.
Interpreters at Colonial Williamsburg "knead" the clay to remove large non-clay particles, which in the 2,000°F heat would crack the brick. Visitors are invited to knead by hand or feet, but that process is slow and tedious. In colonial times, indentured servants and enslaved workers processed the clay by stepping on it repeatedly in a mud pit. Even children could be assigned that task, which would not have been pleasant work on a cold day.
Colonial Williamsburg also uses a pug mill to mix the clay. Pug mills became common by the mid-1800's, and were essential in industrial operations after the Civil War ended slavery. In a pub mill, horses or mules turned a blade inside a barrel to mix raw clay and water. Mixing creates a homogeneous product, so a brick will bake consistently.
Colonial Williamsburg uses a pub mill to increase productivity in order to manufacture the thousands of bricks needed for annual construction projects. The alternative, tasking interpreters to mix the clay with their feet, might affect employee retention...
Once the clay is a consistent mixture, interpreters make bricks by hand. During the summer months, they place mud in a wooden mold that defines the shape of the final product. Most molds are rectangular, but some include rounded edges to make the coping bricks on top of walls and used as decorative features.
Clay is brought to the interpretive exhibit from about seven miles away. At various times, clay from different sources might have different percentages of sand. Colonial brickmakers could adjust the size of their molds to account for the different shrinkage, in order to create bricks of a consistent size.
bricks are made from clay that is shaped in a mold, then dried before firing
Source: Mads Bolton, Historic Trades and Skills of Colonial Williamsburg (June 21, 2024 Facebook post)
Each brickmaker had his own molds. They were not standardized with one particular size throughout the colony, in contrast to the standard modern 4"x2.25"x8" brick. Each brickmaker produced their version of a standard product, and masons used mortar as needed to align bricks in a wall.
Fine sand was used to coat the interior of each mold before the mud was slapped inside, then leveled at the top. Without the sand, the mud would stick inside the mold. Molding bricks was a repetitive process requiring physical labor without intellectual stimulation:2
Workers would dump the soft mud brick out of the mold and place it in the sun. For the first 2-3 days, the bricks were laid flat and not on their narrow side. That required more space, but minimized the wet mud's tendency to expand sideways and get flattened due to gravity.
The fresh bricks were covered initially with a tarp or straw so they would not dry out too quickly and crack. The next step was to flip the partially-dried bricks onto their sides and remove the cover, so air and sunlight could dry the bricks thoroughly.
After about a week of drying out, the bricks would be stacked underneath a wooden roof to keep them out of the rain. Shade avoided exposure to daily direct sunlight which would also dry bricks too quickly, creating a friable stack of mud which would fall apart and be useless. Bricks would continue to dry until enough had been produced to justify building a brick kiln/clamp.
Bricks were made from mud during the summer, when the temperatures were warm. In colonial Virginia, bricks could not be made in the winter. Water in the brick would freeze and crack the clay before it could dry and be fired. Winter still required work. Firewood was cut then, so it would dry over the summer and burn hot the following fall.
As much as a pound of water would evaporate from each brick as it dried. By late September, all the bricks to be fired would be sufficiently dry and in a sheltered place. After crops had been harvested in the fall, additional labor was available for loading the wood required to fire a kiln sometime between October and December. Waiting until the end of hurricane season in September minimized the risk that a heavy rainstorm would drench a kiln and ruin the brickmaking effort.
The brickmaker's labor crew, typically enslaved workers in the 1700's, built the kiln/clamp in a process could require several weeks. Already-fired bricks were placed on the bottom, then several thousand "green" bricks were stacked carefully. A series of tunnels were left at the bottom of the pile for the firewood, and the air required for the wood to burn.
kiln construction starts with laying down a set of "benches" on which unbaked bricks will be stacked in arches ("corbels")
Above the tunnels, bricks were aligned in rows designed for hot air to pass through. Stacks of bricks ended up being 10-15 feet high, if the demand was sufficient. On the outside of the kiln/clamp, fresh mud would be smeared on old bricks so the exterior sides were sealed. Gaps were left so the ends of tunnels at the bottom of the stack were exposed on two sides.
The tunnels at the bottom were large enough so laborers could shove wood inside them from either side. The width of a kiln/clamp was limited; it was essential that wood be inserted into the middle so heat from the fire would cook all of the bricks in the stack. After the wood was initially lit, more wood was added regularly. Making bricks required that a hot fire be kept burning for 4-5 days at the bottom of the kiln.
dried mud bricks are stacked to create a kiln, inside which the bricks will be heated to 2,000°F
Source: Mads Bolton, Historic Trades and Skills of Colonial Williamsburg (September 18, 2024 and October 18, 2024 Facebook posts)
Within the kiln, bricks were stacked close to each other but not touching on the sides. That spacing allowed heat to rise from the wood fires in the tunnels, gradually raising the temperature within the kiln. Controlling the flow of air was essential. The exterior of the kiln was lined with old previously-fired bricks which were covered with mud, and metal covers were used to control the amount of air that could enter the tunnels at the sides of the kiln. Except for the ends of the tunnels and the open top of the stack, the exterior of the kiln was insulated and made to be air-tight and control the heat flow.
the exterior of a brick kiln was insulated with old brick and mud, with bricks to be fired stacked inside
Source: Mads Bolton, Historic Trades and Skills of Colonial Williamsburg (November 18, 2024 Facebook post)
The brickmaker's special skill was in controlling the temperature inside the kiln. It not heated enough, the final product would be soft salmon-colored bricks. Those would crumble when exposed to rain. If heated too hot, mud bricks would melt together and create a pile of useless metamorphosed clay fused together instead of separate bricks.
To start the firing of the kiln, small sticks of wood were ignited in the tunnels. For the first few days, those tunnels were left open all day and night as the temperature inside the kiln rose. Larger pieces of firewood were added gradually as the fires became self-sustaining underneath the stacked mud bricks. As fresh wood was added, hot embers were pushed into the center at the bottom of the pile. Careful alignment of the firewood and embers was required to heat all the bricks evenly, as the temperature inside the entire kiln slowly increased.
The initial temperature was kept around 350°F. Hot air moving through the stack slowly forced remaining moisture out of the clay, which the brickmaker could observe as rising steam.
firewood shoved inside the tunnels heats the bricks stacked within the kiln
Source: Mads Bolton, Historic Trades and Skills of Colonial Williamsburg (November 23, 2024 Facebook post)
Until the start of the firing, a tarp above the top of the stack would be used to keep the still-soft bricks dry during a rainstorm. Later in the process, rising heat from within the kiln made a covering unnecessary - and unrealistic, since any cover would burn unless it was raised far above the kiln.
When the brickmaker saw the initial heating was successful and there was no longer steam vapor rising above the kiln, he would direct that more firewood be added to increase the temperature to roughly 1,400°F-1,800°F. The higher temperature and access to fresh air burned whatever material in the clay would oxidize, fully dehydrating the brick.
After about three days, the openings for the firing tunnels within the kiln were closed with metal or stone covers. The covers were removed only briefly when more firewood was being added. Heating the kiln required wood to be added about every hour, all day and night. Roughly a cord of wood was burned for each 1,000 bricks manufactured.
The bottom of the stack, where the wood was burning on the ground, had the highest temperature. In the final stage, with the firing tunnels closed for most of the time, temperatures next to the embers reached 2,000°F or even hotter. The middle of the kiln would be 1,800°F and the top would be around 1,600°F.
In the high temperature, clay particles gradually vitrified and melted together to create a water-resistant metamorphic brick. Temperatures varied by location within the kiln, affecting how the clay of each brick fused together. Bricks exposed to lower temperatures, often at the edges of the kiln, ended up being softer and less waterproof. Such bricks were used for interior walls.
Bricks exposed to higher heat, ending up with the clay particles very tightly fused, were used for foundations and exterior walls. "Clinker" bricks that became too brittle, after being overheated, could be used as rubble between interior walls. Such bricks could also be broken up and mixed into the next batch of clay.
Iron in the clay oxidized in the heat, creating the red color of a well-fired brick. Bricks at the top would be a lighter red. Potash in the wood would glaze the exterior of the bricks near the tunnels, adding a black color and making then more watertight. As bricks were removed from a cooled kiln, they would be sorted into different piles for different uses in a building.
The first masons in Virginia were brought by the Virginia Company to Jamestown to make hearths and other structures from bricks that were imported from England. Jamestown archeologists have determined that brick ovens were built in a kitchen cellar inside James Fort, soon after the first colonists arrived. The brick retained the heat needed to cook food. In the morning, wood fires were lit inside the ovens to heat the bricks and surrounding clay. After the coals were removed from the hot oven, dough could then be placed inside to bake bread.
After Sir George Yeardley arrived in 1610, the English colonists began to manufacture bricks from local clay. Wood and clay were plentiful in Virginia; it was the labor which was scarce.
Dutch bricks were imported to Jamestown starting around 1630. They came as ballas or perhaps as cargo for construction. Dutch bricks are yellow-brown rather than red, because the Dutch clay was rich in calcium but low in iron. The Dutch bricks lack the iron oxide (rust) which creates the red color of bricks made from Virginia clay.3
settlers at Jamestown made bricks for construction of a church, New Town houses and the Statehouse, and the National Park Service has excavated a kiln
Source: J. Paul Hudson, A Pictorial Booklet on Early Jamestown Commodities and Industries (illustration by Sidney E. King, 1957)
A colonial brickmaker had to calculate the amount of wood to burn each day, in order to create the preferred temperature. The brickmaker used several clues to determine when to stop firing the kiln. The color of the bricks glowing different shades of yellow within the stack, as seen through the tunnels, indicated if the desired temperature had been reached.
Bricks would shrink as the moisture in the clay boiled away, and the top of the stack would slump slightly in response. Throughout the firing, the brickmaker would climb a ladder to view the top, If the slumping was more pronounced in one part of the stack, more wood would be added at one tunnel or air flow would be modified to smooth out the distribution of heat.
When the bricks had been cooked sufficiently, the coverings around the tunnel would be sealed with clay and the pile left to cool. After about a week, the mud and exterior bricks would be stripped off the sides of the kiln and the newly-fired bricks could be unstacked.
A wealthy person, church vestry, or government agency would contract with a brickmaker to produce enough bricks for each structure. The brickmaker, typically someone who moved from project to project as contracts became available, would acquire a crew of enslaved and free blacks to perform the tedious labor tasks. Two white brickmakers directed the enslaved workers who made the bricks in the 1790's for the new Executive Mansion (White House) in Washington, DC.
The laborers became skilled as they selected and made the clay, molded the bricks, and fired the kiln. It is likely that some enslaved workers managed brickmaking operations in locations where there was a regular demand, as opposed to one-time projects for small mansions in rural areas where only one season of manufacturing was required.
A hearth, fireplace, and chimney would require around 12,000 bricks. The George Wythe House in Williamsburg required 250,000 bricks, the Capitol in Williamsburg required 600,000 bricks, and the Governor's Palace used 1-1.2 million bricks.
Where to locate a brick kilns was a judgement call. When Thomas Jefferson first built Monticello, the kiln was very close to the construction site for the house. Bricks from the kiln that were too soft even for interior walls was used with dirt to reshape the topography and create the lawn around the mansion house. In 1774, perhaps at the suggestion of the workers at the kiln, he calculated that it would require less labor to locate the kiln closer to the raw materials and moved it down the hill:4
colonial brickmakers were traveling businessmen who went to places where customers were building a new structure
Source: Virginia Chronicle, Virginia Gazette (December 17, 1772, p.3)
The Wren building at the College of William and Mary is the the oldest academic building still in use in the United States. However, the kiln constructed in 1695 to manufacture the bricks for the new college was the very first building. An archeological study in 1932 noted:5
A modern assessment of the structure noted:6
Making mortar to place between the bricks was also a labor-intensive process. Oyster shells were collected to provide a source of lime. Shells were baked in a wood-fueled kiln, or sometimes just a stack of shell and firewood layers, to convert calcium carbonate (CaCo3) into quicklime or calcium oxide (CaO).
When water was added to the calcium oxide powder, another chemical reaction created slaked lime or calcium hydroxide (Ca(OH)2). That product could be applied directly to farm fields to raise the pH of soil; increased alkalinity enhanced plant growth.
To create the mortar used for constructing brick buildings, slaked lime (calcium hydroxide) was mixed with sand, crushed oyster shells, and more water. That produced the gritty slurry which was placed between bricks. That slurry was not used immediately; it was allowed to cool before being applied. Cooling gave time for quicklime/calcium oxide still remaining in the mix to convert into slaked lime (calcium hydroxide) and become stable for the long term. If the mortar was applied immediately, too much remaining quicklime could expand in the mortar between the bricks and the pressure would create cracks.
Modern science has revealed that having some quicklime in the final product can be beneficial. The Romans made concrete that included quicklime, creating an exothermic reaction which heated the material. Not all of the quicklime/calcium oxide in the "hot mixing" process was converted into slaked lime (calcium hydroxide). Small particles of quicklime known as "lime clasts" were trapped in the final product.
When cracks allowed water to seep into Roman concrete, the lime clasts would then transform into slaked lime (calcium hydroxide) and calcium carbonate which gradually sealed the cracks. The final product was a self-healing, resilient concrete.
The Romans also used pozzolana, a volcanic ash, when making their concrete mixture. Pozzolana reacted with other materials to create crystals shaped like flakes and needles that bonded other concrete particles tightly. Roman concrete has supported buildings such as the Pantheon for 2,000 years.
Mortar chemistry is critical to maintaining historic structures. Settling and age requires repointing the walls occasionally. Repointing is a process in which crumbling mortar, which no longer holds bricks in place, is replaced with new mortar.
The modern mortar mixture known as Portland cement is more watertight than the mortar created in colonial times. In old buildings, moisture moves from inside the building and though walls via the mortar. If modern mortar is used in repointing, that moisture will end up passing through the bricks. The bricks will gradually decay and weaken the wall.
In addition, modern mortar is stiff and will not shrink/swell consistently with old brick. Preservation architects now specify that repairs use a mortar mix that matches what was used in original construction. To match appearances, the color of new mortar can be adjusted as needed to create the historic "look" by adding clay or modern pigments.7
Machinery to manufacture bricks was created in 1885. Mass production facilitated construction of houses, commercial buildings, and industrial plants in cities across the United States. Modern tall buildings rely upon an internal steel frame for support and use bricks for exterior facing, but there are still 10,000,000 bricks in the Empire State Building in New York City.8
after several days, tunnels within the brick kiln are fueled hourly and then sealed
wood is added to the kiln night and day for about five days
prior to the Civil War, enslaved workers unstacked the fired bricks from the kiln
A brick building in colonial Virginia was a sign of permanence as well as wealth. The first brick building in Virginia was constructed in 1638-39 at Jamestown by Richard Kemp, who had been appointed as Secretary of the colony. Governor Harvey described the house as:9
The oldest intact brick structure in the United States is Bacon's Castle in Surry County. It was built by Arthur Allen in 1665, and is today owned by Preservation Virginia. During a restoration project in 2025, workers found a brick with the imprint of a kitten's paw. The imprint survived because that particular brick was protected from the elements, after being put into the interior of a 20' thick wall. At other colonial sites, bricks have been found with prints of dogs, pigs, and of course the human hands that originally shaped the clay.10
Source: Colonial Williamsburg, Meet the Brickmakers!
Source: Townsends, The Ancient Art Of Brickmaking - Impervious Building Blocks Handmade From The Earth
During the colonial period, skilled brickmakers were itinerant workers. They traveled from project to project to guide the process, particularly construction of the kiln and firing of the bricks. Enslaved workers at the job site did the physical labor to mix the clay, mold the bricks, and cut the firewood. After a year or two to create several hundred thousand bricks for one mansion or public building, the brickmaker moved to the location of the next customer and obtained a new workforce.
Brick manufacturing evolved from a cottage industry into an industrial process after the Civil War. As urban areas created a concentrated and steady demand for bricks, brickmaking plants were constructed with machinery to mix and extrude clay into the desired shapes. A skilled workforce which lived nearby made the bricks, and the product was shipped to the construction site rather than manufactured there.
Alexandria County (renamed Arlington County in 1920) was a major center for brick manufacturing at the start of the 20th Century. Clay was excavated along the Potomac River shoreline, then molded into shape and fired to become bricks for construction projects in Washington DC. In 1903, production was estimated at 100 million bricks. One plant had six kilns, each with the capacity to produce 300,000 bricks.
"Brick City" developed at the southwestern end of Long Bridge. The site later became known as Crystal City, and then National Landing after the arrival of Amazon.11
factories making bricks for buildings in Washington, DC were concentrated on the Potomac River shoreline of Alexandria County in what today is Crystal City/National Landing
Source: Library of Congress, The vicinity of Washington, D.C (by Griffith Morgan Hopkins Jr., 1894)
Insider, How Bricks Are Made