Preserving Historic Buildings Quiz | Humanities

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1. In historic preservation it is important to know the age of the building needing repairs, the types of materials used, and how those materials were originally worked, so that the restoration of the building fits seamlessly with the original. One of the best ways to determine the age of a wood building (the most common building material though the 19th Century) is to look at the cut marks. Different types of log cutting techniques overlap through the years, so they're not used exclusively to date wooden structures, but they provide a good base point for determining a range of years in which a building was constructed. Of the following, which cut pattern alludes to a wood building constructed before 1700?

Answer: The checkerboard pattern of hand hewn wood

Looking at saw marks, while not giving a specific year, gives a range of years in which a wood building was constructed. It gives preservationists a great point to start. The four main distinctive patterns of wood cuts are the checkerboard pattern of hand hewn wood, the angled V-cut of a man-powered pit saw, the parallel vertical cut line of a frame saw mill, and the curved/arced pattern of a circular saw.

Hand hewn wood dates from around 1620 to about 1810. The distinctive checkerboard pattern is created by and adze, a flat headed tool which is used on the top and bottom of logs to remove wood and create a flat surface.

V-shape pit saw marks are seen in wood dating from around 1700 to 1830. These marks are both vertical and at an angle of 25-30 degrees with the vertical. When pit saws were in use, to cut the wood into the desired shape, the felled tree was placed horizontal across the opening of a "pit". The pit was just the space under the tree and not necessary in the ground. One man would stand above the pit and one would stand below. With each man holding an end of a long pit saw, they would push and pull the saw and move along the length of the tree, cutting off excess wood, or slipping it into smaller pieces.

The parallel vertical lines of a frame saw mill are seen from about 1800 to 1860. Frame saws were often powered by water mills and had blades like huge modern bandsaws. As water turned the waterwheel attached to the frame, the saw would move up and down, and the wood would be drawn past.

Circular saw marks have been seen in wood since the late 1800s, and they are the saw of choice is modern wood-frame construction. The best way tell the age of wood with circular saw marks is to look at the radius of the arced marks. More historic wood had curved cuts of a very large radius compared to the cuts made from modern circular saws. Wood cut before 1910 most often has a curve radius of 5'. Wood from between 1910 and 1935 has a curve radius of 3'. Wood cut post-WWII has a curve radius of 16". Most professionally cut modern wood has a curve radius of 12".

2. Another common way of dating wood frame buildings is to look at tree-rings. This is especially useful in timber construction, where the whole of the tree is used. When dating trees, each year is read as a combination of one light and one dark ring of the tree trunk. Each spring growth period of the tree is seen as a light ring, with the corresponding summer growth seen as a dark ring. The study of these rings has a special name. What is the study of tree rings called?

Answer: Dendrochronology

Dendrochronology is the study of tree rings (dendro- means "tree"). Agrobiology is study of plant nutrition and growth in relation to soil. Cytomorphology is the study of the structure of cells. Geochronology is the study of the age of the Earth.

Counting tree rings is the easiest way to determine the age of a tree. The pattern of dark and light rings is distinctive and each set corresponds to a year. Dark tree rings, in most locations around the world, appear in the summer when weather is relatively dry. The dark color is dense growth and the bands of dark wood are often much narrower than the bands of light wood. The light color is less dense growth where the bands are wider. These light tree rings, in most locations, appear in summer growing seasons where weather is relatively damp. In some places, such as the western United States, wet and dry seasons are reversed and the pattern of light and dark tree rings is reversed accordingly. All trees of like wood will have the same growth pattern of rings for the same time period throughout a region. Knowing the ring pattern seen in cut wood can help determine the original location of the tree.

3. Historically, wood structures have a relatively short life-expectancy. Untreated wood, used in most pre-20th Century construction, is prone to deterioration by termites and other insects, yearly freeze-thaw cycles, and repeated wet-dry cycles that cause dry-rot. What remains when the wood deteriorates are the metal mechanical devices of connection, such as screws and nails. These screws and nails are excellent tools to aid in the dating of historic structures. Like wood cut patterns, different screws and nails represent different time periods of wood construction. Screws, first seen in wood construction as early as the 1700s, pre-date the use of nails in construction. However, the evolution of nail design was faster than that of screws. Which of the following nail types was used in US wood construction first, in the late 1700s/early 1800s?

Answer: Forged nails with stamped heads

Before mechanical fasteners like screws and nails were used in wood construction, wood frame members were connected using mortise and tenon joints. In mortise and tenon joints, one piece of wood has a hole cut into it, usually by a chisel, and a second piece of wood is formed with a protrusion that can fit into the hole. The protrusion is often a little larger than the hole, so that a solid connection is made when the two pieces are forced together. Friction between the wood pieces is what holds mortise and tenon joints together. In addition to mortise and tenon joints, wood pegs were often used to hold pieces of lumber together, and operated using the same principle, with friction as the binding force.

The first mechanical fasteners were seen as early as the 1700s, when metal screws were introduced. Until around 1840, screws were made without tapering. In the late 1800s, the Phillips-head screw was produced. It was not until the last decade or so of the 20th Century before square heads and patterned grips became widely used.

Nails started being widely used as fasteners around the turn of the 18th Century. The first nails used were forged nails, which were popular before 1810 and had four sloped edges and a stamped head. The nail of choice between 1805 and 1860 was a cut nail. A cut nail is a nail which is cut from a piece of sheet metal. It has two parallel sides and two taperin sides. After 1860, round wire nails with stamped heads became popular. In 1920, round wire nails with modern heads began to be widely used. Plancher nails, with sharp points and flat heads, are a modern invention. Such nails are used to attach overlapping wood floorboards, so that the mechanical connections are invisible.

4. In addition to wood, brick has been a common material in building construction for centuries. Brick patterns and colors have changed over time and are useful in dating buildings. The preservation of brick buildings has its own set of challenges. It is very common in brick buildings for water to infiltrate the mortar that binds the bricks together. This causes a lot of problems in brick walls, including the very common spalling, or popping off of the front, of bricks. To fix this problem in brick (or stone) a procedure called repointing is carried out. In repointing, the color, density, strength, and pattern of both the bricks and the mortar must be matched. The mortar used in the repointing must have the characteristics of being less dense and more flexible than the bricks or the wall will fail under compression and the bricks will spall again. Which ingredient of modern mortar should be avoided when repointing historic masonry?

Answer: Portland cement

Traditional brick mortars were composed of water, sand, and lime. Such mortars were less dense and more flexible than the historic bricks they kept in place. In order for a mortar to be effective, it needs to be less dense and more flexible than the surrounding bricks so that it can act as a shock-absorber of the forces in a wall. If the mortar is not less dense and more flexible than the surrounding bricks, then forces build up in the bricks, causing the brick faces to spall. Portland cement should never be used to repair historic mortars. It is dense and relatively inflexible, and would cause more damage than good to historic brick structures. Portland cement should only be used with modern, completely-machined brick, which is both hard and dense.

A common way to date buildings is by looking at the pattern of the bricks in the exterior walls. Popular brick patterns, called bonds, have changed through the centuries from the English bond, to the Flemish bond, to the American bond. English bonds were popular in 16th and 17th Century England and America. The Flemish bond was popular around the time of the English Civil War. The American bond was most popular during the mid-1800s. All three types of patterns are seen in load bearing, structural brick walls.

Most modern buildings do not have solid brick walls, but have hanging brick facades. It is easy to spot a non-load bearing wall because of a distinctive brick pattern called a running bond. In a running bond, all the bricks in the wall are oriented in the same direction, whereas in load bearing walls some of the bricks are oriented perpendicular to the face of the wall to tie back into the wall for support. The running bond has only been used since the late 1800s.

5. Another common problem in brick and stone construction caused by water infiltration through mortar is the collection of salts on the surface of bricks and stone. Both brick and stone are porous materials which means that water can wick through them. A lot of early brick and stone buildings were constructed with mortars that contained salts. When water enters into the mortar layer of brick and stone buildings, it picks up the salts, which are then drawn through the brick or stone and are deposited on the surface. The salts are seen as patches of white that cosmetically deface the facades of such masonry buildings. The salts are not harmful to the structure and can be washed away. What is the technical name for these white salt deposits on the faces of bricks and stones?

Answer: Efflorescence

Efflorescence is the exposing of salts on the surface of a brick or stone. While efflorescence on a masonry building does not look pretty, it is important to note that such salt deposits are not harmful or damaging to the brick/stone or to the integrity of a masonry wall. Efflorescence is easily removed with a steam cleaning. Steam cleaning, however, is not a permanent solution. Since the efflorescence originates in the mortal of a brick wall, it will continue to come back again and again until all the salts in a mortar are removed. Repeated steam cleanings are necessary, but eventually the efflorescence will stop coming back.

Poultice is a chemical plaster-like material that can be used to help with the removal of efflorescence from a brick wall. It is plastered onto the surface of brick effected by efflorescence, covered with a plastic bag, and left to harden for a day. It is then chipped off and neutralized. Tempering is a process in brick-making that unifies the density of the clay before bricks are fired. Hydraulic fracking has no connection to bricks, but is used in the petroleum and natural gas industry.

6. In historic stone buildings, in particular, there is a type of problem that occurs when metals are inserted into the stone. This problem often arises when metal gates are used to close stone entryways. This problem, called oxide jacking, occurs when the metal is exposed to water (rain or humidity) and rusts. When metals rust, or oxidize, they expand. When this oxidation occurs to metals encased in stone, the force of the expanding metal causes spalling in the stone. Which of the following metals does not readily oxidize, and is therefore safe to use in conjunction with stone?

Answer: Bronze

Bronze is an alloy of copper and tin. Copper on its own will oxidize in a process called getting a patina, but the tin in bronze protects the copper from oxidation. Bronze is safe to use in conjunction with stone and brick because, without oxidation, it will not expand and spall of the face of the stone. Cast iron, wrought iron, and aluminum all oxidize and expand in damp conditions and are therefore not appropriate to use with stone.

There are many cases where iron railings or gates have been used with stone, and in all cases, the iron rusts, discolors the stone, and the stone breaks apart because of the stress caused by expansion of the rusting iron.

7. Cleaning historic buildings must be done with care. Often times harsh methods are used to clean dirt, rust, and salt deposits from the facades of brick and stone buildings. These methods can permanently destroy the faces of bricks and stones, leaving the building "scarred". Of the following, which is the safest and most effective method of cleaning a brick or stone building?

Answer: Steam

Steam is by far the gentlest and most effective method of cleaning brick and stone buildings. As long as water infiltration is not a problem with the side of a building, steam is the preferred method of cleaning. It doesn't damage the surface of bricks or stones, and it easily removes dirt and salt buildups that may mark the brick or stone.

In some cases, like that of efflorescence a second accepted method of cleaning is the use of chemicals. When using chemical cleaners, however, it is important not to use anything that could etch the stone on the surface of a building. Sandblasting should never be used to clean a brick or stone building.

It permanently damages the faces of brick and stone and can leave pockmarks in a wall. Sandblasting changes the color and the surface texture of brick and stone, and the damage it causes is irreversible. Scraping is not an accepted method of cleaning brick and stone facades.

8. Clay products are very commonly seen in historic buildings from brick to porcelain and terra cotta. Bricks are normally used in wall construction, terra cotta is most often seen in roof covering, and porcelain is most often seen in interior fixtures like sinks. All three materials start out the same, as soft clay. Whether the initial clay becomes brick, porcelain, or terra cotta, is determined by how the clay is fired. What is the correct distinction between the firings of terra cotta, brick, and porcelain?

Answer: Terra cotta is fired once; brick and porcelain are fired twice.

Brick is fired at the lowest temperature of the three clay materials, at temperatures of 900-1000 �C. Porcelain is fired at the highest temperatures of 1,200 �C and 1,400 �C. Terra cotta is fired at the intermediate temperature of 1000�C. Both brick and porcelain are fired twice, but terra cotta is only fired once.

In structural, load bearing, brick walls, different qualities of bricks are used for different purposes. Bricks are graded based on how close they were to the fire during the firing process. The bricks that were closest to the fire and charred or glazed, are the darkest in color, and are used for looks. Mid-sized bricks are the best for use on facades. Harder bricks are used on exterior facades (except the front) and softer bricks are used for the interiors of walls. Bricks that are the farthest away during firing are not used in wall construction, but are used as pavers.

9. The environment plays a large part in the weathering and deterioration of buildings. Wind, water, temperature changes, and settling earth can all cause problems with both modern and historic buildings. Which environmental factor is the greatest threat to the conservation of historic buildings?

Answer: Water

Water is a killer of buildings. It can enter a building several different ways and cause devastating structural damage. There are four main ways water can enter a building: through the roof, the walls, the openings, and the foundation. In wood construction, a layer called a water barrier, or a vapor barrier can be adhered/fastened to the exterior of the wood to keep water from coming into contact with the wood. In concrete construction, the concrete can be sealed with chemicals or special plasters to keep water out. In brick construction, it is impossible to keep water from penetrating through a wall. Brick, by nature, is a porous material and it does not hold chemical sealers. Because brick is often used as decoration for the exterior of a building, it is impractical to cover it with a plastic layer. In the case of brick, water is allowed to pass through the exterior layer of brick into an airspace behind the wall which is protected on the interior by a waterproof barrier. At the base of all brick walls, there are gaps in the mortar, called weep holes, which allow water that has passed through the bricks to drain away from the wall.

Roofs are protected from water by various types of overlapping coverings from terra cotta tiles, to slates, metals and rubber shingles. In each case, the layers are stacked and overlapped so that water can only travel downhill. Water has the capability to wick upward, and the overlapping of roof coverings creates a waterproof system that keeps water from wicking up and into the underlying structure. Openings such as windows are often sealed with waterproof tape and caulk which keeps water off the exterior. Windows also often have a lip that angles away from the opening and that has a groove to keep water shed from entering through the window. It is impossible to keep foundations completely dry, so to aid in keeping water out of basements, drainage systems of gravels and corrugated pipes are used to move water quickly and effectively away from the exterior surface of a foundation.

10. In more modern times, metals have been used in buildings from reinforcing rods (rebar) to railings, flashings, and roof fasteners. Common metals used in historic construction are cast iron, wrought iron, steel, copper, bronze, and aluminum. Each metal has its own strengths and weaknesses. Some metals are structural while others are decorative. Some metals oxidize and rust while others do not. In addition, some metals cannot be used in conjunction with others. When metals such as copper and iron are used together, there is a transfer of electrons from iron to copper. This process is called galvanic action, and the metal which loses its electrons corrodes. The metal which gains electrons does not corrode and is given a special name. What name is given to a metal that gains electrons through galvanic action?

Answer: Noble

Metals which gains electrons through galvanic action are called "noble" metals. The most commonly used non-precious noble metal used in construction is copper. Common precious noble metals are silver and gold. They are resistant to corrosion and oxidation in most air, and gain electrons through galvanic action.

There are only a handful of metals that are considered to be noble by the definition that noble metals are resistant to corrosion and oxidation. However, in the case of galvanic action, when two metals are placed in contact with each other, the more "noble" metal will always attract the electrons of the less "noble" metal, causing the less noble metal to corrode and oxidize.

It is very important, when using a combination of metals in construction, to avoid using metals such as iron and tin in conjunction with copper, because copper will always take the electrons in galvanic action.

11. In historic buildings, a very popular roofing material is slate. Slate is a metamorphic rock that is fine-grained and can be split into thin, smooth layers. Slates come in a variety of different colors and are extremely durable, which makes them ideal for use in roofing. The color of a slate is different depending on the location in which is it found. Because of its durability and look, slate is the most expensive roofing material. Many historic buildings used slate roofs, despite the cost, because of the long-term life of the stone. Buckingham Slate, quarried in Virginia, has a life longer than 300 years. Slate has a form of deterioration that occurs slowly over time and is different from all other roofing materials. How does slate deteriorate?

Answer: It delaminates.

Slate deteriorates by delaminating. The structure of slate is such that is formed in very thin layers that stack on top of each other into a solid stone. It is metamorphosed rock which makes it highly durable, capable of lasting for hundreds of years. The unique structure of slate, which makes it so long-lasting, means that it is also very poor in tension. Because slate is poor in tension it must be hung, not nailed, to the underlying roof structure. Copper is the only metal that can be safely used to hang slate.

Other common roofing materials used in construction are terra cotta tiles, rubber shingles, wood shingles, and metal (such as copper and tin). Terra cotta tiles are very poor in compression and can easily shatter under the weight of a person (or snow), and are used only in warm climates. Rubber shingles can become brittle in the cold, and can dampen with water, which cause them to break off or to mold. Wood shingles not properly sealed which are exposed to rain, snow, or even just humidity, can rot. Metal roofing can deteriorate by oxidation (rusting), and with copper being in high demand, are also prone to being stolen.

12. Often in historic buildings, cracks occur in walls and foundations. There are four different types of cracks that can occur in buildings. Three types of cracks are easily fixed and one can bring down entire buildings. There are horizontal cracks caused by early general settlement, vertical cracks caused by uneven settlement, diagonal cracks caused by shear/sliding forces, and patched "cracks" caused by water infiltration. Which type of crack is the most serious and can bring entire buildings down to the ground?

Answer: Shear diagonal cracks

Shear cracks are extremely dangerous and can bring entire buildings down to the ground. Shear cracks occur when there is uneven tension or compression stress in a building. They occur when buildings have poor foundations, or the bearing loads in buildings are unequal. Horizontal cracks and vertical cracks both occur early in the life of a building and do not necessarily cause structural damage to a building.

In most cases of vertical and horizontal cracks, if the cracks are properly patched and sealed there is nothing to worry about. If they are not properly patched and sealed, water can enter through the cracks and cause real structural damage. Water infiltration patches are not necessarily structural, and most of the time are not anything to worry about.

13. A foundation is the base on which a building stands. It transfers the loads of a building into the earth, and helps to keep water out of buildings. In modern buildings, foundations are most often made of concrete with layers of waterproofing and with drainage along the sides to transport water away from the walls. Historically, foundations were made of stacked/layered stones with smaller stones on the exterior to help drain water away from the building. In some places foundations are very shallow, and in others they are very deep. In tall, heavy buildings, it is preferable for foundations to go all the way down to bedrock. In smaller buildings there is no need to go so deep. There is a general rule for the depth of a foundation in relation to the "frost line" to avoid uneven settling and upheaval of a building. A frost line is the depth to which the ground freezes in the winter. What is the general international rule for foundation depth?

Answer: A foundation must extend below the frost line.

The general rule for foundations and the frost line is that the base of the foundation must extend to below the level of the frost line. In most places, this means at least 2' below the frost line to be safe. The depth of the frost line differs from location to location around the globe. The frost line is deeper toward the north and south poles and nonexistent near the equator. Above the ground surface, foundations generally extend up to 16" above grade to keep out bugs and termites.

If a foundation does not extend far enough below the frost line the building can upheave when the ground freezes. Upheaval and uneven settlement are very common causes of building collapse. The Leaning Tower of Pisa is a great example of uneven settlement, where the building sank into the ground on one side, causing the building to tilt sideways. In cases where it is impractical to build walls on a foundation, piles (large concrete columns) can be placed in the ground to be used as a foundation. These piles are generally only used in skyscrapers or where soil is very soft, and a lot of the time they extend down to bedrock, well below the frost line.

14. From the 1860s to the 1970s the most common and most effective fireproofing material was asbestos. It came in several forms including felts, shingles, and vinyl-asbestos tiles. It is now known that asbestos fibers in the air can cause asbestosis, mesothelioma, and lung cancer. Many people walk on vinyl-asbestos tiles all the time and are not in any danger. As long as the tiles are intact, the asbestos does not pose any threat and should be left alone. Only when the tiles start to fracture do they become a health hazard. To remove hazardous asbestos, contractors need to be specially certified because the removal of asbestos tiles (and its other forms) can cause more fibers to become airborne. What is the term used to describe something which is brittle and easily fractured or crumbled, like asbestos tiles when they need to be removed?

Answer: Friable

Friable is the only one of the options that means brittle and easily fractured or crumbled. The word "friable" is most often used when talking about asbestos. When asbestos tiles, for example, lose their elasticity and their corners begin to fracture off, they are said to be friable, and need to be removed. Vinyl asbestos tiles were commonly manufacture in 9" x 9" squares.

When original tiles began to fracture, releasing harmful asbestos fibers into the air, they were removed. A healthy alternative tile used today instead of asbestos tile, is called vinyl composite tile (VCT).

It commonly comes in 8" x 8" and 12" x 12" squares.

15. A very common hazardous material found in historic buildings is lead. Lead was a standard construction material from antiquity until around the 1970s and it appears in many forms from pipes to roofing to paint. Lead roofs were popular until the late 19th Century when its health hazards were discovered. Lead roofs have been gradually replaced by other metal roofing materials. Which of the following lead-alternative metal roofing materials is known for its property of changing color as it patinas?

Answer: Copper

As with the removal of asbestos, it is not always best to remove lead from a building, and if it needs to be removed, specially trained contractors are needed. In some cases, encasing the lead with a solid binder and then painting over it is the best method. In cases involving plumbing, it is usually best to remove and replace the pipes. It is important to encapsulate or remove lead inside a building whenever possible because it can cause severe health problems. In adults and children, lead poisoning can cause neurological disorders and numbness as well as developmental disorders and mental health problems.

When copper oxidizes it patinas to black and then to green. Zinc and tin both rust. Monel is a nickel alloy that is resistant to rust, but may have a slight patina due to its copper content.

Source: Author kaddarsgirl

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