Conservation and restoration of lighthouses

The conservation and restoration of lighthouses is the process by which lighthouse structures are preserved through detailed examination, cleaning, and in-kind replacement of materials. Given the wide variety of materials used to construct lighthouses, a variety of techniques and considerations are required.

Lighthouses alert seagoers of rocky shores nearby and provide landmark navigation. Lighthouses also act as a physical representation to maritime history and advancement. These historic buildings are prone to deterioration due to their location on rocky outcrops of land near the water, as well as severe weather events, and the continued rise of sea levels. Given these conditions preservation and conservation efforts have increased.

Havre De Grace Lighthouse

Exterior

Ground

The ground consists of the land, outbuildings, and landscape that the lighthouse property sits on. The grounds may also include buildings from other time periods as part of the cultural landscape. The types of buildings, their relationship to one another, their location over the whole of the property, types of flora and their location, and potential archaeological sites (if they have been identified), are all aspects that are related to the lighthouse and its history and should be considered during conservation of the property.

Outbuildings are prone to deterioration because they were often used for storage and were not maintained to the same standards as the lighthouse. Former repairs to buildings may have used inexpensive materials as a temporary fix.[1] These materials often degrade making the building unstable. Any buildings that remain intact and in their original location are historically important to the relationship and usage of the lighthouse.[2] Materials, colors, and details are all representative of the lighthouse when it was active and are often considered during the preservation process.[3]

Coatings

Paint

Lighthouse exterior paint was often used in colorful patterns to act as a day marker. Paint was also used to help protect the exterior structure of the lighthouse from wear.[4] Evidence of paint degradation include crazing, cracking, peeling between coats, blistering, and wrinkling. Repair can be made through spot treatments or through a complete replacement of the paint. Original paint was made of lead and tended to withstand harsh conditions while still protecting the structure. The required use of National Historic Preservation approved paints has proved difficult as they do not work well with the lighthouse structure's original materials [5] Furthermore, salt in the air can lead to severe chalking of the paint surface and cause premature failure of latex paint products. Most repainting projects will have to begin with removal of the original base coat, followed by a thorough surface cleaning to remove impurities, then ended with a complete repainting of the structure. Paint normally only lasts between five and eight years, depending on the lighthouse and conditions.

Stucco

Stucco has been traditionally used as a protective barrier on the exterior of lighthouses. Stucco is made up of fine granular particles mixed together with a binder. The composition of stucco has changed significantly over the years and may require laboratory analysis to determine the makeup.[6] Most of the problems with stucco arise from prolonged contact with water or moisture which breaks down the structure of the particles and binder.[7] In addition, the texture of stucco is prone to removal when abraded. As with most preservation, gentle cleaning of the surface can help remove dirt and impurities and inhibit further deterioration.

Iron

Iron was a popular material used in lighthouse construction. Multiple types of iron were used including: cast iron, wrought iron, steel, galvanized iron, galvanized steel, and stainless steel. Cast iron was the most popular material because it resists corrosion and can be cast into a multitude of shapes. Though iron is sturdy it can be prone to deterioration through corrosion (oxidation, galvanic corrosion, and graphitization), weathering, and flaws from the manufacturing process. Degradation of iron is visible through pitting, cracks, erosion, rust, blistering, flaking, and scaling.

Preservation and restoration of iron should be completed using the least invasive approach possible. Iron is strong but can be easily damaged through improper or harsh procedures. "Many of the maintenance and repair techniques... particularly those relating to cleaning and painting, are potentially dangerous and should be carried out only by experienced and qualified workmen using protective equipment suitable to the task. It may be necessary to involve a USCG engineer or architect, preservation architect, or building conservator familiar with lighthouse preservation to assess the condition of the iron and prepare contract documents for its treatment."[8]

Masonry

The masonry component of a lighthouse is made up of the bricks and stones on the exterior. Damage to masonry is primarily caused by water, salt accumulation, expansion and contraction, abrasion, poor ventilation, and inappropriate cleaning techniques (ex. sandblasting). Masonry may show many signs of deterioration to include: bulges, cracks, efflorescence, erosion, flaking, sloping or uneven settlement, mold or mildew, missing stones or bricks, condensation buildup, and blistering.[9]

Cleaning of Masonry

Basic preservation of lighthouse masonry usually includes gentle surface cleaning. Appropriate methods for cleaning are determined by the type of masonry that exists on the building. Some cleaning methods include water, chemical, and laser.[10] There are multiple water cleaning methods. Soaking is a process where the masonry undergoes a prolonged exposure to misting water to remove dirt. Water washing uses a light to medium pressurized stream of water. Some water washing may use the addition of detergents to increase dirt removal. Chemical cleaning is also an option, but may be too harsh depending on the makeup of the masonry. Chemical cleaners are either acidic or alkaline. Laser cleaning is effective, mostly on smaller areas of masonry, but can be costly. Occasionally, a lighthouse may be weatherproofed through covering the masonry with paint, stucco, or whitewash/lime mortar wash; but only if these are historically accurate for the structure. Due to the differences in materials and construction techniques, only an experienced architectural conservator should be contacted for conservation or restoration work.

Wood

Wood was either used for construction on the exterior or in combination with masonry and/or iron to build components of the lighthouse (ex. stairs). The largest cause for deterioration of wood in lighthouses is from exposure to moisture. This exposure is normally the result of direct and prolonged exposure to damp conditions. Other causes for deterioration include pests, fungus, and insects. Some signs of decomposition include cracking, bulging, holes, peeling paint, leaning of the structure, gaps between joints, and exposed bare wood.

Some complications from wood deterioration can be solved through tight fitting seals around windows and doors, gutter systems, caulking of seams and joints, and sloping away of decking from the structure. Regular cleaning of the surface may also help reduce accumulated residues on the wood thereby prolonging its usable life. The most common treatment for replacing degraded wood is to use a splicing technique where new pieces of wood are joined with original wood features. For severe cases, large in-kind replacements may be necessary.

Interior

Most lighthouse interiors were simple in construction and decoration, unless used as part of the light keeper's residence. A majority of the issues related to lighthouse interiors stem from moisture, condensation, neglect, or inappropriate treatments.[11] Addressing issues on the exterior is required first in order to protect the inside of the structure. Proper ventilation of the structure should be considered. The season and geographical location of the lighthouse will determine what type and how often air exchanges should take place within the lighthouse. According to the National Park Service "the absolute minimum air exchange for most mothballed lighthouses consists of one to four air exchanges every hour; one or two air exchanges per hour in winter and often twice that amount in summer."[12]

Lantern

The lantern is the large round glass structure, that houses the lens, located at the top of the lighthouse. This structure is made out of multiple materials, primarily glass, wood, and iron.

Any conservation or restoration processes should keep in mind that the lantern, ventilation shafts, and lens should not be obstructed in anyway. Any replacement glass must be rated for wind standards that are likely to occur at the top of the lighthouse.

Lantern with a lens inside

Lens

The Fresnel lens was introduced for use in lighthouses around 1823. Generally, keeping the lens historically preserved, rather than restoration to period, will reduce stress on the lens and keep some of the lens's story intact (e.g. chips of the glass that are documented in historical light keeper's notes).[13] It is important to consult a conservator before attempting any conservation on a lens. The glass that was used to make the lens is often brittle and may chip easily. Lens glass etches easily from contact with oils or dust.[14]

To secure the prisms of the lens a compound of calcium carbonate, lead, and linseed oil, called litharge, was used. If deterioration of the litharge is found, it is likely that the prisms are not properly secured within the frame structure of the lens.[15] If the litharge is white in color (lead carbonate) the material is mostly non-porous and may not easily be preserved, meaning that full litharge replacement might be necessary. If the litharge present is orange-red in color (lead-oxide), this substance tends to be more porous and may allow for stabilization.[16]

Originally, the lens was "floated in a trough of mercury"; though this practice has been abandoned, mercury contamination may still exist in the area.[17]

Cleaning a lens

Documentation of the prism normally begins with labeling all issues starting from the center prism, listed as number one, and then working outward sequentially. Identification should indicate whether it is an upper or lower prism. Prisms are checked for firm seating by gently tapping on the outside of the glass only. If there is any movement of the glass, conservators are normally called before any work is continued. If the glass is stable, the prisms will then be checked for particulate matter. If fine or non-abrasive particles are observed, a soft cotton cloth lightly wetted with distilled water may be used to gently clean the surface. It is also possible to use denatured alcohol mixed with water to clean the glass.[18] The solution will vary from lens to lens as each has a different glass composition. A conservator should be called in if any clouding of the glass is found as this is a sign of glass deterioration.[19]

In the past, a routine polishing of the brass that secures the lenses would take place. In preventive conservation, the task of brass polishing should not take place as it encourages loss of original material. The patina that develops over time also helps create a protective barrier around the brass.

Disaster planning

Lighthouses are inherently prone to disasters due to their location. A disaster plan can help mitigate some of the issues that occur during a disaster situation. Most disasters are water related but fires, earthquakes, and especially erosion can also be causes. The disaster plan should be tailored to the disaster most likely to affect the lighthouse's location; however, it should take into regard multiple types of disasters. The lighthouse property and objects located within it should be thoroughly documented. Furthermore, complete photograph documentation of the property and collection can help with insurance claims and restoration. There should be a copy of these documents located at the lighthouse as well as a secondary location in case they may not be accessible at the lighthouse due to a disaster. Coordination with local authorities, like the police and fire department, may help during an emergency situation. Ideally, files should both be digitized and on paper.

Moving a lighthouse

Strong winds and waves cause land erosion around lighthouses. Over extended periods of time, the promontories that lighthouses are normally built on can be eroded to the point where the safety of the lighthouse is impacted. In extreme cases, the lighthouse might need to be relocated to a new plot of land in order to preserve the structure. There are four major lighthouse moves that have taken place in the United States: Block Island Southeast Lighthouse, Cape Hatteras Lighthouse, Sankaty Head Lighthouse, and Gay Head Lighthouse.

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References
  1. "IALA Lighthouse Conservation Manual" (PDF). International Association of Lighthouse Authorities.
  2. Secretary of the Interior's Standards and Guidelines. "Treatment of Historic Properties, 1995". National Park Service.
  3. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
  4. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
  5. "Piedras Blancas Lighthouse Preservation Expertise". American Lighthouse Council. Archived from the original on 2016-05-26. Retrieved 2016-04-17.
  6. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
  7. Preservation Briefs. "The Preservation and Repair of Historic Stucco". National Park Service.
  8. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF).
  9. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF).
  10. Preservation Briefs. "Assessing Cleaning and Water-Repellent Treatments". National Park Service.
  11. National Park Service. "Lighthouse Preservation Handbook" (PDF).
  12. National Park Service. "Lighthouse Preservation Handbook" (PDF).
  13. Byrne, Greg. "The Conservation of the Classical Lighthouse Lens" (PDF). United States Lighthouse Society.
  14. Commandant Instruction 16500.9. "Classical Lens Maintenance" (PDF). Retrieved 24 April 2016.
  15. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
  16. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
  17. Commandant Instruction 16500.9. "Classical Lens Maintenance" (PDF). Retrieved 24 April 2016.
  18. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
  19. National Park Service. "Historic Lighthouse Preservation Handbook" (PDF). United States Lighthouse Society.
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