Large Powder Magazine Final Report.pdf

FORT JEFFERSON

Large Detached Magazine

Dry Tortugas National Park, Florida

August, 2017

Acknowledgments All research, documents, and drawings were produced through a generous donation from the

HTR Foundation in an effort to preserve Civil War era structures at Dry Tortugas National Park.

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ADMINISTRATIVE DATA

GENERAL bACkGROuND

RESOuRCE bACkGROuND

PHYSICAL DESCRIPTION

TREATMENT RECOMMENDATIONS

APPENDICES

APPENDIx A. DRAWINGS

APPENDIx b. SELECT HISTORIC IMAGES

APPENDIx C. MATERIALS ANALYSIS

Contents

Large Detached Magazine 2016, FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk1

Administrative Data

RESOuRCE NAME AND NuMbERS building Name: Large Detached Magazine

Other Names: Large Powder Magazine

Parade Magazine

Structure No.: HS-02

LCS ID No.: 011916

RESOuRCE LOCATION

The Large Detached Magazine is located along the northern edge of Fort Jefferson’s parade ground near bastion 5. Fort Jefferson is located on Garden key, within Dry Tortugas National Park (DRTO). The Park is located approximately 67 miles west of key West Florida in the Gulf of Mexico and only accessible by boat or seaplane.

The Park encompasses an area of approximately 100 square miles and contains seven small sand and coral keys (islands) and the surrounding shoals and water. Garden key contains the Park’s central cultural feature, Fort Jefferson. The Fort is occupied by Park staff and is the center of Park operations.

The visiting public generally travels to the Park by commercial ferry or seaplane service operated out of key West.

Location: Parade Ground Fort Jefferson, Garden key, Dry Tortugas National Park

Coordinates: 24° 37’ 46” N Latitude 82° 52’ 50” W Longitude

County: Monroe

State: Florida

CuLTuRAL RESOuRCE DATA

The Large Detached Magazine was listed on the National Register of Historic Places in 1976 as a contributing element of the Fort Jefferson National Monument Historic District.

In 1992, Dry Tortugas National Park was established by Public Law 102-525 to “preserve and protect for the education, inspiration and enjoyment of present and future generations nationally significant natural, historic, scenic, marine and scientific values in South Florida.” under [36 CFR 60.1

(b) (1)], historic units of the National Park Service are automatically given National Register of Historic Places status by virtue of their incorporation into the park system.

Dry Tortugas National Park is currently in the process of updating its National Register documentation.

SIGNIFICANCE

The National Register of Historic Places Nomination Form completed in 1976 includes the following Statement of Significance for Fort Jefferson:

During the first half of the nineteenth century the u.S. began a chain of seacost defenses from Maine to Texas. Though not as extensive in area as Fort Monroe in Virginia, Fort Jefferson, seventy miles west of key West was the largest of all Third System Forts in terms of armament for which it was designed, about 450 guns. built to cover a strategic anchorage in the Gulf of Mexico, it was one of only three forts in the South to remain in Federal hands throughout the Civil War. It was never fully armed or even completed though construction proceeded well beyond the war and into the 1870s. During the post-war years the fort became a prison, housing among others some of the alleged Lincoln assassination conspirators, the most famous being Dr. Samuel Mudd. After serving nearly four years and having helped save many prisoners from yellow fever, Dr. Mudd received a full Presidential pardon. The Fort was virtually deserted in 1874, and it was not until 1900 that it was transferred to the Navy Department. It was later made available to the Dept. of Agriculture who used it as a bird sanctuary until if finally became a national monument in 1935.

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Tortugas Harbor

Large Detached Magazine

Fort Jefferson

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk3

The rich history of the area of Fort Jefferson goes back as far as 1513 when it was discovered by Ponce de Leon and named the Tortugas Islands, Tortugas being the Spanish word for turtle. Since the eight low-lying islands had no fresh water, sailors called them Dry Tortugas.

Pirates operated in and around the Dry Tortugas preying upon ships of all flags. Not until 1821 when Florida became part of the united States were the pirates successfully driven out.

The importance of the Dry Tortugas to the military grew as westward expansion of the country brought more and more commerce to Gulf Coast cities. To prevent enemy seizure of the islands and to insure the control of the Gulf of Mexico shipping, a decision was made to erect a Fort somewhere on the islands Fort Jefferson served this purpose by being the key to control of the Gulf of Mexico because of its strategic location. Commerce from the Mississippi Valley to the Atlantic coast passed through this vital area. The Fort was begun on Garden key in 1846 and was later named Fort Jefferson in honor of the former u.S.

President.

During the 30 years of construction, Fort Jefferson was a quiet place with the Civil War the only event to bring major changes in building or life.

Federal troops hurriedly occupied the half-completed, unarmed fortress in

January 1864. The development of the rifled cannon rendered Fort Jefferson obsolete long before construction was stopped.

Hurricanes and yellow fever, coupled with the obsolescence of the fortification led to the abandonment of the fort by the Army in 1874 with the work still underway. During the 1880s and 90s, the Navy looked upon Fort Jefferson as a re-coaling station for its Caribbean fleet. From Tortugas Harbor, the battleship Maine weighed anchor for Cuba, where she was blown up in Havana.

One of the first naval wireless stations was built at the Fort early in the 20th century and, during World War I, the area was equipped as a seaplane base. As the military moved out again, fires, storms and salvagers took their toll, leaving the “Gibralter of the Gulf” the vast ruin it is today.

The National Register Nomination states specifically of the Large Detached Magazine:

Located near the northeastern bastion inside the fort, this barrel-vaulted magazine was built to serve as the main powder storage area. Its shell-proof arch was turned in 1866. The walls were raised 13 1/2 feet, and if completed would have covered the arch which stands about 30 feet high. The magazine is structurally sound, except for bricks on the parade ground face, which have been extensively damaged by weapons being fired by soldiers into the side of the magazine. The dimensions of the magazine are approximately 60’ x 90’.

Section 12 of the National Register nomination establishes the Level of Significance of Fort Jefferson as National.

The nomination does not specify a Period of Significance, however in March 2004, a “Record of Decision” was issued establishing the Period of Significance for the Fort and its associated resources as spanning from 1846 to 1876.

RELATED STuDIES byrd, beth W. and Susan L. Hitchcock, Garden key, Dry Tortugas National Park, Cultural Landscape Report, 2011.

bears, Edwin C., Fort Jefferson National Monument, Historic Structure Report, Historical Data Section, 1983.

Lord Aeck Sargent Architects. Fort Jefferson National Monument, Historic Structure Report Amendment, 2004.

Manucy, Albert, A Constructional History of Fort Jefferson , 1846 - 1864, National Park Service, 1981.

Morrison, George T., Phillips, John Wesley and Revised by Richard Rasp. National Register of Historic Places Inventory- Nomination Form for Fort Jefferson National Monument, February, 1976.

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Ever 7121 - Ca. 1937 image of Large Detached Magazine with timber centering in place.

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk5

General background

From the start of construction on Fort Jefferson in late 1840s there were challenges securing adequately durable and strong brick. When construction appropriations were approved in 1844, most Florida brick manufacturers were still making brick using hand-presses. Due to unreliable local transportation and the slower pace of local brick manufacturing, additional bricks for the Fort were shipped from manufacturers as far away as New York and Maine. However, northern bricks were not suited for the tropical marine environment of the Fort and decayed quickly.

The outbreak of the Mexican-American War in 1846 delayed any substantial progress on the Fort, so it was not until 1850 that the Army began to find sources for the massive quantity of bricks the fort’s construction would require. In December of 1850, Captain Wright, the Fort’s superintending engineer, visited several existing Gulf Coast forts to observe the condition of their bricks and ascertain where those bricks were made.

Wright identified brick made in the Pensacola area as preferable for its ability to withstand the salt and high humidity of the Tortugas, but brick manufacturers and shipping companies in the area were still lacking in their ability to produce adequate bricks and ship them to the construction site. Maine bricks were a close second, having already withstood several years in place in piers on Garden key.

Failures by Congress to approve appropriations for the Fort led to more delays in securing and transporting building materials. So, it was not until

1854, that Phillip H. Raiford and General Anderson Abercrombie, influential Alabama businessmen, plantation-owners, and politicians, proposed that they would establish a brick manufacturing business in the Pensacola area to supply bricks for the construction of Fort Jefferson and Fort Taylor.

The War Department quickly approved, despite Raiford and Abercrombie’s inexperience in brick-making. A contract dated August 24, 1854 shows that Raiford and Abercrombie agreed to supply 3,000,000 bricks of specific dimensions and quality, at $21 per thousand, to each fort.

Raiford and Abercrombie’s inexperience led to continued delays in establishing their plant on Escambia bay in Pensacola. While they set up their facility, they secured bricks from other manufacturers to supply to the forts. In 1855, when Raiford and Abercrombie began producing and supplying its first bricks, they proved to be substandard, breaking and crumbling easily. The company was at risk of losing their contract to provide bricks for the forts. Financial stresses led Phillip Raiford to sell his interest in the company to John E. bacon in 1857. During this time, bricks and other building supplies for the fort were being transported from the northeast, a more expensive, slower, and difficult endeavor – shipwrecks were not uncommon.

A decision by the newly incorporated bacon and Abercrombie to hire master brick-maker, John W. Crary, saved the company from demise. Crary immediately improved the hand manufacturing process to a point that the bricks made by the company now satisfied inspectors at the forts. Shortly thereafter, Crary began inventing and implementing a mechanized process for brickmaking that automated and shortened many manufacturing steps while producing stronger and more durable brick. The reliability of shipping bricks to the forts also improved with the securing of a contract in 1858 with the key West shipping firm, Tift and Company. The supply of high quality bricks to the forts was secured; by 1861, Crary claimed to have supplied over 16,000,000 bricks to the federal government.

In the decade leading up to the Civil War, Florida experienced massive growth in both population and economy. State leaders pushed for expansion of railroads, while landowners expanded their plantations and their slaveholdings – at a time when the national debate over slavery was reaching its peak. During this time, political parties in Florida were in a state of flux; the Whig party had disbanded and two new political parties were challenging a radicalized Democratic Party. Despite their differences, however;

Floridians were mostly united in their dislike of the Republican Party, predominantly due to the Republican platform against slavery in the new territories. Not one vote was cast in Florida on November 7, 1860 for Republican presidential candidate Abraham Lincoln.

Following Lincoln’s election, a convention was held in which delegates voted on whether to immediately secede from the union or to ‘cooperatively’ secede along with the other southern states. Florida elected to secede immediately and passed an Ordinance of Secession on January 10, 1861. Many of the other Confederate states

Challenges with logistics, building materials, and appropriations create significant delays in construction at the fort.

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were also scrambling to pass Secession legislation. With secession imminent, Florida state leaders quickly organized state militias, supplying them with arms and ammunition.

Progress was slow, however, as Florida’s limited transportation networks and still sparse population made communication and organization challenging.

Florida’s senators were also preparing for the state’s inevitable secession, using their status in Washington DC to procure information on united States military activity in Florida, specifically regarding the strength of the garrisons at forts located within Florida.1 It was clear to them that one of the first actions following secession would have to be the taking of all Federal positions in Florida. In fact, an arsenal near Chattahoochee as well as Fort Marion in St. Augustine were taken by state militia just days prior to secession.

In early January, 1861, Fort Marion and the arsenal near Chattahoochee were surrendered without conflict as they were both only guarded by a handful of federal soldiers. by mid-January, 1861, combined forces of southern state militias took control of the naval yard in Pensacola and threatened to take nearby Fort Pickens.2 1 Johns, John E., Florida During the Civil War, university of Florida

Press, 1963, p. 23

2 Nulty, William H., Confederate Florida: The Road to Olustee, The university of Alabama Press, 1990, p.

On February 26, 1861, bacon and Abercrombie, halted all production of bricks for the forts – having sided with the secessionists. In March 1862 the Confederate army ordered all Pensacola industries destroyed out of concern that they might be used by federal forces. bacon and Abercrombie’s brickworks was subsequently burned to the ground and never rebuilt.

Meanwhile, the Federal military, fully aware of Florida’s intention to secede, was strategically reinforcing its southern Florida forts, namely Fort Taylor in key West and Fort Jefferson on the Tortugas. both forts were extremely important strategic posts for naval and commercial activities in the Gulf of Mexico, with construction beginning roughly 15 years prior as part of the united States’ Third System of coastal defenses.

However, both forts required significant work to be adequately prepared not only for any possible attack, but also to accommodate the increase in the size of their garrisons.

Captain M. C. Meig, Corps of Engineers, arrived at Fort Jefferson on November 8, 1861 and noted that the fort had “not a single gun”.

No attack ever came, but construction on the forts continued throughout the Civil War and in to the following decade.

Despite the logistical challenges of securing and transporting material, the fiscal shortfalls from insufficient appropriations, and two wars, some progress was made at the Fort.

by the end of the Civil War, the Fort’s walls were nearly complete; there were several sections of barracks and officer’s quarters, kitchens, a hospital, a chapel, and several wood buildings; and, foundations for several more buildings had been laid.

Over the next decade to 1876 when the fort was finally abandoned, the officer’s quarters and barracks, and their associated kitchens, were completed; the Large Detached Magazine had walls and its barrel vaulted arch; the small magazine’s foundations were set; and many of the embrasures, casemates, and barbettes were mounted with guns.

However, in 1889, George Phillips, the Fort’s overseer and employed at the Fort since 1846, noted that most of the buildings at Fort Jefferson were in a state of dilapidation.

“Everything here is going to destruction… The once fine quarters of the Officers and Soldiers are now but a little more than a wreck.” Phillips also noted widespread vandalism by salvagers taking brass hardware, windows, and doors.

Drawer 74, Sheet 80 - Fort Jefferson, Dry Tortugas, Fla, Sketch showing Condition of Works June 30th, 1867, to accompany annual Report.

Large Powder Magazine

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk7

Resource background

As initially designed by Totten, Fort Jefferson was to have five, two-story magazines (two 48 by 28 feet and three 30 by 28 feet). As well, the two casemates of each long curtain wall were to be used as magazines. Each tower bastion also held a small magazine. Plans for the fort were approved by the Secretary of War on November 16, 1846.

The earliest drawing that shows powder magazines within the fort’s parade ground is a plan from 1846 (Drawer 74, Sheet2) entitled “Projected Fort for Garden key” that overlays the fortification onto a survey of the island prepared the previous year. The drawing shows a total of five brick magazines along with various other structures planned for construction within the parade ground. The structures are generally arranged parallel to each of the fronts, leaving the center of the parade ground open. The drawing shows two different magazines, three roughly square magazines measuring 52’ x 53’ located near bastions D, E and F and two larger magazines measuring 52’ by 70’ along fronts 1 and 3 near bastions b and C.

The Mexican-American War of 1846-1848 and a 14-month (May 1852-August 1853) suspension of work due to failures by Congress to approve appropriations for construction, created significant delays in the work. Continued shortfalls in appropriations and the overarching difficulty in securing and transporting quality construction materials to the Tortugas meant that only the main walls of the fort and several “temporary” wood-frame buildings were built in the first decade and a half of construction.

When captain Meigs, the Fort’s new superintending engineer, arrived on site in November of 1860, he remarked “not a single gun… could be found.” The first guns eventually did arrive in January of 1861, shortly after Florida announced their secession from the union. However, the parade magazines were still not started and so munitions were stored in the smaller magazines of the bastions and curtain walls.

Captain Morton, who replaced Captain Meigs in February 1861, received new drawings of the parade ground magazines in December of 1861. Chief Engineer Totten instructed Morton to start work at once on one of the largest magazines, and stressed the formation of the magazine grillage to prevent subsidence, a growing problem for the works completed thus far. Construction of the new magazine was estimated to cost $32,862.

The Civil War further delayed construction at the fort and so, by June of 1864, only the grillage of the magazine was laid. It was at that time estimated that it would take 550,000 bricks, 150 barrels of lime and 5,000 barrels of cement to complete the magazine.

Despite having only completed the foundations of the Large Detached Magazine, by 1865, foundations were begun for the small magazine.

The parade magazines were continued but never finished; by June 1866 the walls of the large magazine had reached a reference of 13’ 6” and the principal arch turned. It was estimated that 566,000 bricks and 2,036 barrels of cement had been expended to date. In the decade after 1876 only maintenance was completed and by 1891, all magazines in the fort were emptied of gunpowder and munitions.

Timber centering installed to support the brick work of the principal arch during construction remained in place until the early 1960s.

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DRTO 7122 - Ca. 1937.

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk9

Timeline

Large Detached Magazine shown on early plan of Fort

Jefferson Approved November 16, 1846 [Drawer 74, Sheet 2]

ARMY

June 1864 - Grillage for the Large Detached Magazine is laid and concrete brought up to the proper reference - No brick work had commended. (Manucy p. 117)

April 12, 1861 , Southern forces fire upon Fort Sumter, South Carolina

April 9th, 1865, General Robert E. Lee surrenders at Appomattox, VA

January/February, 1862 - General Totten instructs Morton to start work at once on the Large Detached Magazine (Manucy p. 90)

1865 - Foundation for Large Detached Magazine completed (Manucy p. 139)

1866 - Arch of Large Detached Magazine turned (Manucy p. 150)

1868 - Walls of Large Detached Magazine raised 13’-6” (Manucy p. 155)

THE CIVIL WAR

1860 - Montgomery C. Meigs arrives at Garden key replacing

Captain Daniel Woodberry as Superintending Engineer in charge of construction of Fort Jefferson (CLR p. 8).

April 1861 - Lieutenant James St.

Clair Morton replaces Meigs as

Superintending Engineer.

December 29, 1845, The united States annexes Texas

February 2, 1848, Treaty of Guadalupe signed

THE MExICAN-

AMERICAN WAR

January 1874 - Garrison transferred to Fort barrancas leaving only a few soldiers to look after the armament and ordnance stores (CLR, p. 11)

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NAVY NATIONAL PARk SERVICEMARINE HOSPITAL

SERVICE

ARMY

April 1988 - Historic Structure Report indicates condition of

Large Detached Magazine is one of relative stability, the structure being situated in the protected confines of the parade ground. The brick are showing signs of weathering in some areas, particularly on the south and west elevations. (Historic Structure Report, p. 19)

1992 - Dry Tortugas National Park established.

TIME SCALE COMPRESSED

1970 - “physical status report stated that the arch was in good condition but needed repointing and sealing to prevent the mortar from leaching out.” (Garden key Cultural Landscape Report, 2011)

2006 - Historic Structure Report Amendment indicates Large Detached Magazine remains in stable condition but continues to suffer from deficiencies identified during earlier investigations including deteriorated mortar joints, leaching mortar and isolated areas of brick loss/collapse at building corners and vent openings. (HSRA p. 157)

1950 - Timber centering of main arch remains visible in 1950 images of magazine.

January 1, 1935 - Fort Jefferson designated a National Monument by President Franklin Delano Roosevelt

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September, 1939

September, 1945

July, 1914

November, 1918

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk11

Physical Description

The Large Detached Magazine is located towards the northeastern portion of the Fort’s parade ground, parallel to Front 5.

The multi-wythe brick masonry structure sits on a slate water table course, which is above a below-grade concrete bearing wall.

According to research collected in [Manucy and the HSR], the foundation is a wood grillage laid on a sand base.

The structure is roughly 56’ by 80’, including the primary magazine structure of about 60’, a fortified vestibule of about 15’, and ventilation chimney of about 4‘. The 8’ think walls rise to 14’- 8”; their full finished height was meant to be roughly 20’ – 9”. Rising above the walls another 15’- 8” is the principal barrel-vaulted arch, which consists of four independent wythes of brick. The thickness of the walls is not entirely brick; in non-bearing portions the walls are filled with a coral aggregate and natural cement mix. The walls feature narrow openings as part of a passive ventilation system.

The plan of the magazine matches closely with what is shown in the fortification drawings. below the water table course, the interior of the magazine features the angled concrete walls and concrete floor of a cistern, divided in to four chambers by brick partition walls. Above the water course is an open area flanked by four vaults along each long wall. A modern flight of brick stairs leads diagonally down to the floor of the cistern and to some interpretive signage.

The vestibule, which is about 20’ narrower than the main structure, features door openings on both its short sides, at the intersections with the end wall of the magazine. The door openings lead to vaulted corridors that first lead away from the magazine at right angles to the doors, then join and return back towards the magazine through a narrow opening. Each opening, two from the parade ground in to the vestibule and one from the vestibule to the magazine, were to have iron-reinforced wood doors, as specified in the drawings. Some brass pintels still remain in stone masonry within the door frames. Missing brass pintels appear to have been forcibly removed as evidenced by patterns of missing and damaged brick.

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Coral concrete infill

FLOOR PLAN

Stone water table

Principal arch

Ventilation channel

Multi-wythe brick Masonry Wall

AxONOMETRIC VIEW

75’ - 4”

Modern brick stair and rail

Vestibule

Entrance

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk13

View of Large Detached Magazine looking northwest.

View of interior of magazine.

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View of Large Detached Magazine looking southeast.

View of Large Detached Magazine looking east.

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk15

Treatment Recommendations

Treatment to stabilize the Large Detached Magazine will require limited repairs to small isolated areas of brick loss and more widespread repointing of deteriorated mortar. No conditions were observed that threaten the short term stability of the structure, however areas where bricks have fallen from the wall should be repaired as a priority to avoid the permanent loss of historic fabric and the development of more significant failures requiring greater intervention and investment of resources.

Long term preservation of the Magazine will require ongoing observation to monitor conditions and the rate of material deterioration. This must be coupled with a program of cyclical maintenance to address issues as they arise and maintain the integrity of the structure’s envelope and major features.

because construction of the Large Detached Magazine was never fully completed, there are portions of the structure that are exposed to the elements that were not designed to serve in this capacity. The irregular top surface of the unfinished perimeter masonry walls, the coral concrete infill and the surface of the principal arch would have been protected by a massive wood and concrete gable roof structure had the original design been fully implemented. These elements, along with the magazine interior, have now been exposed to the weather for more than a century and are experiencing the deteriorative effects of this exposure.

Given this, treatment strategies should integrate measures to increase durability against moisture infiltration and weathering without compromising the integrity of the architecture.

Areas of mortar deterioration are generally concentrated along the base of the Magazine, at the top of the exterior masonry walls, at building corners and at the underside of the principal arch. Where deterioration is most severe, the mortar has significantly weathered within the joints or it has lost its structural qualities and ability to bind the masonry together. This has resulted in areas where individual bricks have shifted or fallen from the wall. These failures have generally occurred at building corners, at the top of the brick veneer wall, and at the ventilation channels .

Examination of the top surface of the principal arch was performed from the terreplein using binoculars,. Despite its direct exposure to the elements, the sky-facing surface of the arch is in generally good condition with no major signs of failure observed.

The materials present on the interior of the magazine were observed to be in generally good condition. Areas of mortar deterioration are concentrated at the vaulted brick ceilings and along the base of the structure. Evidence of moisture migration through the masonry walls is apparent throughout. Deposits on the interior walls suggest the lime binder is being dissolved and brought to the surface by the moisture.

Recommendations for treatment include the following:

• Remove volunteer plants and vegetation from the structure. Implement a program of vegetation management to keep the structure free from higher plant forms that could potentially damage masonry.

• Repoint areas where mortar has deteriorated or lost its binding qualities.

Develop compatible repair mortars based on results of materials analysis.

At least two mortar types appear to have been used in the construction of the Large Detached Magazine, The mortar used to lay up the walls appears to be a natural cement mortar similar to that used in the construction of the scarp walls. A second mortar type was used to point the brick masonry walls.

Analysis reveals the pointing mortar to be a lime mortar with no evidence of gypsum or other cementitious materials observed (See Appendix C).

• Reconstruct isolated areas of masonry collapse/brick loss at top of exterior walls, building corners and ventilation channels using salvaged brick.

• Fill in gaps and crevices in coral concrete infill to prevent erosion of material and unchecked moisture infiltration.

• Preserve areas of masonry damage along west elevation presumed to be caused during the historic period when the south wall was used as a backstop for small arms target practice.

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STRuCTuRAL RECOMMENDATIONS bY SILMAN

Overall, the Large Power Magazine appears stable and little to no structural intervention is required.

The parapet walls at areas around the Large Detached Magazine have displaced and there are a number of vent channel walls that have collapsed inward. Refer to architectural drawings and narrative for repair at these locations.

Silman observed that the arch is constructed in four separate arches, with no visible header courses tying them together. The outer arch appears to have separated slightly from the inner three arches, which is likely a result of it being sky-facing and directly exposed to weather, as opposed to the inner arches which it shields. Some minimal repointing may be desired to fill cracks, however Silman recommends limiting the repointing to maintain the open joint and allow for thermal movement in the structure.

Silman assumed the inner arch to have been shored during construction and then used as the formwork for building the outer three arches, which would indicate that the inner arch is supporting the weight of the outer arches. However, historic photos show that the shoring was in place for the construction of all four arches, such that each ring can be assumed to support itself and share lateral load equally. Original construction drawings show the intent to build a wood and concrete gable roof over the arches, indicating that they were not intended to be exposed to direct wind or rain.

FORT JEFFERSON, DRY TORTuGAS NATIONAL PARk17

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APPENDIX A. DRAWINGS

Drawings obtained from the South Florida Collections Center

Everglades National Park

Drawer 74, Sheet 12. Detached Magazine

Drawer 74, Sheet 63. No. 53. Fort Jefferson, Plans Sections and Elevations of a Detached Magazine

Drawer 74, Sheet 63. Fort Jefferson, Plans Sections and Elevations of a Detached Magazine

Drawer 74, Sheet 80. Fort Jefferson, Dry Tortugas, FLA, Sketch showing Conditions of Works June 30th, 1867 to accompany annual report.

APPENDIX B. SELECT HISTORIC IMAGES

Images obtained from the South Florida Collections Center

Everglades National Park

DRTO 300892 - Ca. 1899.

DRTO 300936 - Date unknown.

EVER 7122 - Ca. 1937.

EVER 7121 - Ca. 1937.

DRTO 301695 - Ca. 1945.

DRTO 301253 - Date unknown.

DRTO 301551 - Date unknown.

DRTO 301556 - Date unknown.

APPENDIX C. MATERIALS ANALYSIS

Petrographic Examination of Mortar (ASTM C856 and ASTM C1723)

Acid Digestion Analysis of Mortar (ASTM C136)

Water Vapor Transmission and Coefficients of Hygric and Thermal Expansion of brick

Prepared for: Mr. David B. Woodham, P.E.

Atkinson-Noland & Associates, Inc.

Boulder, Colorado

Prepared by: David Rothstein, Ph.D., P.G., FACI Report No.: DRP16.1504

9 DECEMBER 2016

Petrographic Examination of Mortar Samples from Fort Jefferson, Dry Tortugas National Park, Florida

DRP Consulting, Inc. 3200 Carbon Place #104 Boulder, CO 80301 www.drpcinc.com

Fort Jefferson Mortar Petrography Report No. DRP16.1504 Summary Report 9 December 2016

EXECUTIVE SUMMARY

Three (3) mortar samples from Fort Jefferson located in Dry Tortugas National Park, Florida are subjects of petrographic examination to characterize the general composition and condition of the materials represented by the samples. The findings from this scope of work indicate that the three mortars have similar aggregates and distinctly different binder compositions. The sand is carbonate in composition and has a nominal top size of 1.18 mm (#16 sieve) in the Small and Large Powder Magazine mortars and a nominal top size of 2.36 mm (#8 sieve) in the Engineers Officers Quarters mortar. The sand consists of a variety of limestones and shell fragments. The sand content appears higher in the Engineers Officers Quarters mortar with tighter particle packing than was observed in the other samples

The Small Powder Magazine mortar has a lime-gypsum binder. Occasional lime lumps were observed and rare particles of anhydrite rimmed by gypsum and ettringite were observed.

Relatively large, tabular aggregations of material rich in ettringite with minor anhydrite were also observed commonly. These may represent fragments of a material rich in calcium and aluminum (such as clay) that were used production of the mortar and are now pseudomorphed by ettringite.

The Large Powder Magazine mortar is a lime mortar with no evidence of gypsum and no evidence of other cementitious materials observed. Numerous nodules of burnt limestone and burnt lime were observed as were partially burnt fragments of limestone.

The Engineers Officers Quarters mortar has a binder phase that consists of lime and a cementitious phase typical of a historical natural cement such as Rosendale cement.

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1.0 INTRODUCTION

Mr. David B. Woodham, P.E. of Atkinson-Noland & Associates, Inc. (ANA) located in Boulder, Colorado requested DRP Consulting, Inc. (DRP) to perform petrographic examinations of mortar samples collected from Fort Jefferson located in Dry Tortugas National Park, Florida. The purpose of the investigation is to characterize the general composition and condition of the mortars represented by the samples. On 10 November 2016 Mr. Woodham delivered three (3) mortar samples to DRP. Table 1 summarizes information regarding the identification of the samples.

Fort Jefferson was constructed between 1845 and 1876 such that no information regarding the original project materials are available. The location of the structure on a remote island in the Gulf of Mexico provides exposure to heat, salt, destructive weather systems and water. No information was provided regarding the field conditions attending the areas that provided the samples listed above.

2.0 SCOPE OF WORK

The testing involved petrographic analysis of each sample according to ASTM C856 [‑ ] 1 supplemented with scanning electron microscopy (SEM) and energy-dispersive x-ray spectrometry (EDX) as described in ASTM C1723 [‑ ]. This report summarizes the findings of 2 this scope of work; Appendix A-Appendix C contains the notes, photographs and micrographs from the petrographic examination and Appendix D describes the procedures used to perform the tests.

Table1. Summary of samples

DRP No. Sample IdentiÞcation & Location

20YD8374 Small powder magazine, North wall at entrance

20YD8375 Large powder magazine, Southeast corner

20YD8376 Engineers ofÞcers quarters

! Standard Practice for Petrographic Examination of Hardened Concrete. Annual Book of ASTM Standards, Vol. 4.02., ASTM 1 C856-14.

! Standard Guide for Examination of Hardened Concrete Using Scanning Electron Microscopy, Annual Book of ASTM 2 Standards, Vol. 4.02, ASTM C1723-10.

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3.0 FINDINGS

The following findings are relevant to the mortars represented by the samples. The referenced figures are in Appendix A, Appendix B and Appendix C.

3.1 Small Powder Magazine Mortar The sample consists of a mortar fragment that is 55 mm (2.2 in.) long, 35 mm (1.3 in.) wide and 7 mm (0.3 in.) thick and weighs ~ 17g (0.6 oz.; Figure A1, Figure A2). No embedded objects, cracks or significant microcracks were observed. The mortar is non-air entrained. The aggregate is a natural sand with a nominal top size of 1.18 mm (#16) that consists of limestone and occasional shell fragments (Figure A3). The paste is light gray (Figure A4) and the binder is a very fine-grained mixture of lime and gypsum. Lumps or nodules of hydrated lime and burnt lime were observed along with occasional grains of anhydrite rimmed by ettringite (Figure A5-Figure A7). Aggregations of material rich in ettringite and anhydrite were also observed (Figure A8). These aggregations are tabular in shape and the size of large sand fragments. The entire surface stained purple from phenolphthalein, indicating a lack of carbonation within the mortar paste (Figure A9).

3.2 Large Powder Magazine Mortar The sample consists of two mortar fragments. One fragment is 45 mm (1.7 in.) long, 35 mm (1.3 in.) wide and 7 mm (0.3 in.) thick and the other is 35 mm (1.3 in.) long, 25 mm (1 in.) wide and 7 mm (.3 in.) thick. The combined weight of the samples is ~ 15 g (0.5 oz.; Figure B1, Figure B2). No embedded objects were observed; a few hairline cracks are present. The mortar is non-air entrained. The aggregate is a natural sand with a nominal top size of 1.18 mm (#16) that consists of limestone and occasional shell fragments (Figure B3). The paste is light gray to white with a granular texture and dull luster (Figure B4). The binder is a very fine-grained lime-based mortar with no evidence of anhydrite, gypsum or ettringite observed (Figure B5). The paste contains calcium silicate phases that are carbonated (Figure B6, Figure B7). No portion of a freshly saw-cut surface stained purple from phenolphthalein, indicating carbonation of the mortar paste (Figure B8).

3.3 Engineers Officers Quarters Mortar The sample consists of a mortar fragment that is 60 mm (2.3 in.) long, 40 mm (1.6 in.) wide and 27 mm (1.1 in.) thick and weighs ~ 95 g (3.2 oz.; Figure C1, Figure C2). No embedded objects were observed; a few hairline cracks are present.The mortar is non-air entrained. The aggregate is a natural sand with a nominal top size of 2.36 mm (#8) that consists of limestone and occasional shell fragments (Figure C3). The paste is pale brown gray (Figure C4) and the binder is a very fine-grained mixture of lime and a cementitious phase that is similar to natural cement such as the historic Rosendale natural cement (Figure C5). Carbonated calcium-magnesium silicate phases were observe in the paste (Figure C6, Figure C7). No evidence of sulfate-bearing phases. No portion of a freshly saw-cut surface stained purple from phenolphthalein, indicating carbonation of the mortar paste (Figure C8).

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4.0 CONCLUSIONS

The findings described above indicate that the three mortars have similar aggregates and distinctly different binder compositions. The sand is carbonate in composition and has a nominal top size of 1.18 mm (#16 sieve) in the Small and Large Powder Magazine mortars and a nominal top size of 2.36 mm (#8 sieve) in the Engineers Officers Quarters mortar. The sand consists of a variety of limestones and shell fragments. The sand content appears higher in the Engineers Officers Quarters mortar with tighter particle packing than was observed in the other samples

The Small Powder Magazine mortar has a lime-gypsum binder. Occasional lime lumps were observed and rare particles of anhydrite rimmed by gypsum and ettringite were observed.

Relatively large, tabular aggregations of material rich in ettringite with minor anhydrite were also observed commonly. These may represent fragments of a material rich in calcium and aluminum (such as clay) that were used production of the mortar and are now pseudomorphed by ettringite.

The Large Powder Magazine mortar is a lime mortar with no evidence of gypsum and no evidence of other cementitious materials observed. Numerous nodules of burnt limestone and burnt lime were observed as were partially burnt fragments of limestone.

The Engineers Officers Quarters mortar has a binder phase that consists of lime and a cementitious phase typical of a historical natural cement such as Rosendale cement.

This concludes work performed on this project to date.

David Rothstein, Ph.D., P.G., FACI

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Fort Jefferson Mortar Petrography

Appendices

Appendix A Small Powder Magazine Mortar Petrography (ASTM C856/C1723) Appendix B Large Powder Magazine Mortar Petrography (ASTM C856/C1723) Appendix C Engineers OfÞcers Quarters Mortar Petrography (ASTM C856/C1723) Appendix D Procedures

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Appendix A: Fort Jefferson Mortar Petrography Report No.: DRP16.1504 Sample ID: Small Powder Magazine Mortar (20YD8374) Date: 5 December 2016

1. RECEIVED CONDITION

ORIENTATION &

DIMENSIONS

Fragment of mortar measures 55 mm (2.2 in.) long, 35 mm (1.3 in.) wide and 7 mm (0.28 in.)

thick. The sample weighs ~ 17 g (0.6 oz.; Figure A1, Figure A2).

SURFACES

One side of the fragment is relatively flat and medium gray in color; the other side is more uneven and white.

GENERAL

CONDITION

The mortar is hard and compact.

2. EMBEDDED OBJECTS

GENERAL None observed.

3. CRACKING

MACROSCOPIC None observed.

MICROSCOPIC None observed.

4. VOIDS

VOID SYSTEM

Mortar is non air-entrained and contains less than 1% total air as estimated from visual and microscopical observations (not determined in accordance with ASTM C457).

VOID FILLINGS None observed.

5. AGGREGATE

PHYSICAL

PROPERTIES

The aggregate is a natural sand with a nominal top size of 1.18 mm (#16 sieve; Figure A3).

The rocks are hard and competent; the grading and distribution are relatively even.

ROCK TYPES

The aggregate consists of fragments of limestone and occasional shell fragments. The limestones range from very fine grained (micritic) to medium-grained; some fossiliferous rocks were also observed. Numerous sand-sized particles that consist of ettringite and anhydrite were also observed.

OTHER

FEATURES

No deleterious coatings or incrustations observed. No low w/c mortar coatings observed.

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6. BINDER OBSERVATIONS

POLISHED

SURFACE

Paste is light gray (Munsell 10YR/7/1) and has a smooth texture (Figure A4). The sample was impregnated with epoxy which tends to alter the texture, luster and hardness of the paste.

THIN SECTION/

SEM*

The binder phase is very fine-grained and consist of a mixture of lime and gypsum, based on the observation of lumps of hydrated lime, burnt lime and occasional grains of anhydrite (Figure A5). SEM/EDS analysis detected the presence of calcium silicate phases in the paste that may be from burnt siliceous limestone (Figure A6, Figure A7). Some of these phases are somewhat carbonated, based primarily on SEM observations. As mentioned above, large lumps of material rich in ettringite with vestiges of anhydrite were observed as well (Figure A8).

* Abbreviations as follows: RRCG = relict and residual cement grains; SCM = supplemental cementitious materials; CH = calcium hydroxide; ITZ = interfacial transition zone. Modal abundances are based on visual estimations.

7. SECONDARY DEPOSITS

PHENOLPHTHALEIN Entire surface stains purple (Figure A9).

DEPOSITS

Deposits of ettringite observed in large lumps in the paste; gypsum observed around some anhydrite grains.

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FIGURES

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Figure A1. Photographs showing oblique views of the sample in as-received condition. The red and blue dots show the orientation of the saw cuts used to prepare the sample. The scale is in millimeters.

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Figure A2. Photograph showing the polished surface of the sample. The scale is in millimeters.

(a) !

Figure A3. (a) Reflected light photomicrograph of the polished surface showing overview of aggregate.

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(b) !

(c) !

Figure A3 (cont’d). Transmitted light photomicrographs of thin section showing detail of aggregate in (b) plane-polarized and (c) cross-polarized light. The red arrows indicate particles of limestone and shell fragments.

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(b) !

Figure A4. (a) Photograph and (b) reflected light photomicrograph of polished surface showing overview and detail, respectively of the binder phase of the mortar. Scale in millimeters in (a).

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(a) !

(b) !

Figure A5. Transmitted light photomicrographs of thin section showing components in the mortar in (a) plane-polarized and (b) cross-polarizedlight. The red arrow indicates a particle typical of burnt lime, the yellow arrow indicates a limestone particle and the green arrow indicates a phase that consists of ettringite and anhydrite.

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(a) !

(b) !

Figure A6. Backscatter electron micrographs of the polished surface showing detail of paste. The green box in

(a) shows the area of (b) where the red box and green, red and yellow dots designate areas that provided the EDS spectra shown in Figure A7 (a), (b), (c) and (d), respectively.

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(a) !

(b) !

(c) !

(d) !

Figure A7. EDS spectra indicating elemental compositions of areas corresponding to the (a) red box, (b) green dot dot, (c) red dot and (d) yellow dot in Figure A6. The spectrum and BSE image shown in Figure A6 are indicative of (a) ettringite, (b) limestone that contains minor silica, (c) carbonated calcium silicate hydration product and (c) carbon-rich residue in burnt lime or limestone.

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(a) !

(b) !

Figure A8. Transmitted light photomicrographs of thin section showing detail of mortar components in (a) plane-polarized and (b) cross-polarized light. The red arrows indicate grains of anhydrite; the green arrows indicate ettringite.

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(b) !

Figure A9. Photographs showing (a) overview and (b) detail of the phenolphthalein stained surface. The scale is in millimeters in both photos.

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Appendix B: Fort Jefferson Mortar Petrography Report No.: DRP16.1504 Sample ID: Large Powder Magazine Mortar (20YD8375) Date: 6 December 2016

DIMENSIONS

The sample comprises two chunks of mortar. One measures 45 mm (1.7 in.) long, 35 mm (1.3 in.) wide and 7 mm (0.3 in.) thick and the other measured 35 mm (1.3 in.) long, 25 mm (1 in.)

wide and 7 mm (0.3 in.) thick. The total weight of the sample is ~ 15 g (0.5 oz.; Figure B1, Figure B2).

SURFACES

One side of the fragment is relatively flat and medium gray in color; the other side is more uneven and white.

GENERAL

CONDITION

The mortar is hard and compact.

2. EMBEDDED OBJECTS

GENERAL None observed.

3. CRACKING

MACROSCOPIC

Occasional sub-vertical hairline cracks (~ 100 µm or 4 mil wide) up to 2 mm (80 mil) long observed.

MICROSCOPIC None observed.

4. VOIDS

VOID SYSTEM

Mortar is non air-entrained and contains less than 2% total air as estimated from visual and microscopical observations (not determined in accordance with ASTM C457).

VOID FILLINGS None observed.

5. AGGREGATE

PHYSICAL

PROPERTIES

The aggregate is a natural sand with a nominal top size of 1.18 mm (#16 sieve; Figure B3).

The rocks are hard and competent; the grading and distribution are relatively even.

ROCK TYPES

The aggregate consists of fragments of limestone and occasional shell fragments. The limestones range from very fine grained (micritic) to medium-grained; some fossiliferous rocks were also observed. Numerous sand-sized particles that consist of burnt limestone were also observed.

OTHER

FEATURES

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6. BINDER OBSERVATIONS

POLISHED

SURFACE

Paste is light gray (Munsell 10YR/7/1) to white (10YR/8/1), has a granular texture and dull luster (Figure B4). The paste is moderately soft (Mohs 2.5-3).

THIN SECTION/

SEM*

The binder phase is very fine-grained and is a lime-based mortar, based on the observation of lumps of hydrated lime and burnt lime (Figure B5). SEM/EDS analysis detected the presence of calcium silicate phases in the paste (Figure B6, Figure B7). Some of these phases are somewhat carbonated, based primarily on SEM observations. No evidence of anhydrite, gypsum or other sulfate-bearing phases was observed.

* Abbreviations as follows: RRCG = relict and residual cement grains; SCM = supplemental cementitious materials; CH = calcium hydroxide; ITZ = interfacial transition zone. Modal abundances are based on visual estimations.

7. SECONDARY DEPOSITS

PHENOLPHTHALEIN No staining observed (Figure B8).

DEPOSITS Paste is carbonated.

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FIGURES

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Figure B1. Photographs showing oblique views of the sample in as-received condition. The red and blue dots show the orientation of the saw cuts used to prepare the sample. The scale is in millimeters in both photos.

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Figure B2. Photograph showing the polished surface of the sample. The scale is in millimeters.

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Figure B3. (a) Reflected light photomicrograph of the polished surface showing overview of aggregate; scale in millimeters.

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(b) !

(c) !

Figure B3 (cont’d). Transmitted light photomicrographs of thin section showing detail of aggregate in (b) plane-polarized and (c) cross-polarized light. The red arrows indicate particles of limestone and the green arrows show burnt lime.

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Figure B4. (a) Photograph and (b) reflected light photomicrograph of polished surface showing overview and

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Figure B5. Transmitted light photomicrographs of thin section showing components of the mortar in (a) plane-polarized and (b) cross-polarized light.