This is an Earthcache – as such, there is no physical cache. Instead after examining the building stones of the old jail at the posted coordinates you will answer 3 questions and message me the answers. This earthcache is located in Hanover Courthouse with permission and only available to see during daylight hours.
SANDSTONE
Mankind has used sandstone to construct buildings ranging from homes to cathedrals, or in this case, jails, for hundreds of years. Different types of sandstone vary in their hardness, but it is softer than other stone types, and therefore making it much easier to quarry and shape. This characteristic also makes it very vulnerable to erosion. Wind and water have changed sandstone in nature for millions of years reducing mountains to sand. The exterior surfaces of sandstone buildings and other objects are also soon affected by the same forces that erode stone in nature.
Sandstone is a sedimentary stone formed by the consolidation of individual grains of sand, which are usually comprised of quartz or feldspar. The most common method of consolidation is the saturation of a sand bed by other materials, such as clay or calcite, but sometimes it results from pressure that develops as newer geological layers are deposited on the top of the bed. Sandstone can be found in a variety of colors, which are determined by its mineral composition; the most common are tan, brown, yellow, red, gray, green and white.
Sandstone is the softest of building stones used in architecture. It “weathers” (decays) easily. It is also porous so it absorbs water easily and needs to be kept dry if possible and allowed to dry if it gets wet. It is relatively easy to carve and shape.
The sandstone used as the exterior cladding of this jail most likely came from Aquia Creek, Virginia. This is the same stone used in the construction of the U.S. Capitol and White House in Washington, D.C. Aquia Creek sandstone itself is not optimal as a building stone in terms of durability, as it was already recognized at the time of its selection. Rather, it was chosen because it was locally available and easily worked.
Aquia Creek is a arkosic sandstone formed from the talus of a decaying granite during the Lower Cretaceous period over 100 million years ago, part of the Potomac Group. The sediments were compacted along the Potomac River near the tidewater region, for this reason it probably never had sufficient overburden to compact its layers into dense stone.
Major components of the sandstone include quartz, which gives the stone strength and acid resistance, and smaller amount of feldspars, which give the stone warm coloration. There is also a small amount of iron that provides the red coloration to the stone, appearing in the form of uniform lines, dots, or “stains.” Grains are bound with secondary amorphous silica, but the stone is considered weakly cemented.
WEATHERING
Sedimentary stones such as sandstone are relatively soft, porous and have friable surfaces. The cements that bond the various sediments together are easily damaged by weathering, pollution, or salts. Anything that causes a difference in the behavior of the outer surface of stone structures compared to the inner regions can lead to stresses that eventually cause cracking and the exfoliation of the outer surfaces.
Hanover has a humid, subtropical climate with multiple wet/dry and freeze/thaw cycles. This is caused by moisture freezing inside cracks in rock. Upon freezing its volume expands, causing large forces which cracks spall off the outer surface. As this cycle repeats the outer surface repeatedly undergoes spalling, resulting in weathering that would continually stress weaker areas, and eventually lead to contour loss.
Spalling is a common mechanism of rock weathering, and occurs at the surface of a rock when there are large shear stresses under the surface. This form of mechanical weathering can be caused by freezing and thawing, unloading, thermal expansion and contraction, or salt deposition.
Dissolved salt is carried through the material in water and crystallizes inside the material near the surface as the water evaporates. A cycle of wetting and drying is established, and crystallizing salts exert pressure disrupting the stone. As the salt crystals expand this builds up shear stresses which break away spall from the surface.
Salts can come from many sources. They may be inherent in the stone itself. They can come from the presence of de-icing salts or polluted rain water, from improper cleaning methods, from the setting bed, and even from the base of the stone by capillary action allowing the soluble salts to rise.
PAINTING THE STONE
Can painting the stone prevent or contributed to weathering? When aquia sandstone is painted, the oil penetrates at least 1/16” inch and forms a seal. This seal greatly reduces the absorption of rain water, but in a large building it is almost certain that water can find other places to enter such as joints between blocks, from the ground, or from the tops of walls. If water is penetrates it will spread through the walls, and the paint will prevent evaporation from exiting at the surface. Under such conditions there is a great chance spalling will occur due to frost action.
LOGGING REQUIREMENTS:
To log this Earthcache: Read the geology lesson above. Answer all four questions posted below and send them via e-mail or messenger contacts on my Geocaching profile.
QUESTION 1. Walk around the building. What side (NE, NE, SE, or SW) shows the most weathering? Any guesses to why that is?
QUESTION 2. Which of these do you think has contributed to the spalling here? Freezing and thawing, thermal expansion and contraction, salt deposition, or all three.
QUESTION 3. Do you see any patching or repairs? If so, how are they holding up?
QUESTION 4. Do you feel that adding a coat of sealant or paint would help or hinder the weathering here?
OPTIONAL PHOTO: Posting a photo that readily indicates that you (and anyone else logging the find) are at the location.
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REFERENCES:
1. Old Stone Jail, Hanover Historical Society, hanoverhistorical.org
2. Famous Building Stones of Our Nation’s Capital, USGS, pubs.usgs.gov
3. A Study of the Properties of the U.S. Capitol Sandstone, Hockman & Kessler, NATIONAL BUREAU OF STANDARDS REPORT,4998, Architect of the Capitol, January 8, 1957, govinfo.gov
4. Porous Materials - Common Problems: Spalling, STAIN-PROOF by Dry-Treat, Video, youtube.com
5. CONDITION SURVEY OF AQUIA CREEK SANDSTONE COLUMNS FROM THE U.S. CAPITOL RE-ERECTED AT THE U.S. NATIONAL ARBORETUM, Aloiz, Grissom, Livingston,& Charola, , repository.si.edu