When Well-Intentioned Repairs Go Awry Part II
Cove Point Lighthouse, Maryland’s oldest continuously operating lighthouse, was recently selected as a recipient of a heritage grant from the state. The tower is owned by the Calvert Marine Museum, and a second grant has been applied for to also renovate the keeper’s house with a complete stabilization of the structure, a new roof, windows and extensive interior work. With that completion, the Museum will be offering the house as a rental to the public for one or two week stays, with the chance to do actual lighthouse type work, such as tracking tides and monitoring ships. The ambitious plans include it being historically accurate to 1923, with of course compliance to today’s standards. While exciting, that’s not what caught my eye in this story. What did, was the reference to “self-destructing bricks.”
From the story, the curator of maritime history at the Calvert Museum is quoted as saying:
The lighthouse tower’s bricks are “self-destructing,” because they were covered for years with a form of concrete on the inside and paint on the outside, said Richard Dodds, curator of maritime history for Calvert Marine Museum. “Basically, the bricks can’t breathe,” Dodds said.
The paint will be removed and the concrete will be replaced with a lime mortar, which will allow moisture to leak out of the bricks, he said. The stairs and doorway also will be repaired, among other projects in the lighthouse, he said.
This is a prime example of “waterproofing” done without regard to the original construction of the tower, which was actually made to allow the water to leak out.
Water Managed Walls
Because lighthouses were built near water, and are subject to extremes of weather, their builders generally allowed for a planned intake (and subsequent discharge) of moisture. The last thing anyone involved in lighthouse rehabilitation is use any caulking or waterproofing compounds. In fact, slapping on a coat of waterproofing paint on the outside, while making the tower look nice, actually does a lot more harm than good.
A case in point is Pemaquid Point Lighthouse, which has recently undergone a proper, historically accurate repair. All the offending paint had to be scraped off, as it was causing the water to stay in the walls, rather than leach out as designed. During the harsh Maine winters, this freeze/thaw cycle was causing the walls to expand, and the mortar to crack. It was a well intentioned, but not historically proper paint job that exacerbated the problems, by the use of waterproofing paint. The paint that is applied should be able to breathe.
From the handbook of historic preservation:
Recoat surfaces with a system designed for the masonry substrate brick, stone, or stucco. The system should be designed to breathe so that moisture trapped within the masonry units can escape. This quality is referred to as the permeability of the coating system.
Misconceptions abound with mortar on historic buildings. Many times, vent holes have been caulked over, with the intention of sealing the interior from the weather. But again, those holes are necessary to allow the water to drain out. They may take the form of small holes, or what looks like a missing brick, but they serve a necessary purpose. The cause of cracking is something else that needs to be identified. Oftentimes, it’s thought that it’s just caused by the building settling. The truth is its often caused from embedded steel.
Added for strength, the steel will rust and expand. If these cracks are patched over, it just covers up a more serious problem. And don’t forget natural aging. Most mortar has a life expectancy of 75 years. The fact most of our lighthouses are 150 to 200 years old says a lot about their builders.
Another major problem is the theory that One Size (Mortar) Fits All. This couldn’t be further from the truth. If a mortar is a cement, sand and lime mixture, the proportions have to be exactly matched, otherwise there will be reactions between the materials used, to the detriment of the building. If the mortar used was a lime putty, it has to be replaced with like, for the same reasons as above.
The High Costs of Restoration
All these are reasons the cost of restoration is so high. If we want our lighthouses, or any historic buildings to last for another 200 years, all these factors have to be taken into consideration. It’s not a job for ABS Construction down the street. Tests have to be done, assessments need to be made, and sometimes extreme repairs such as rebuilding walls need to be undertaken. Even the cleaning has to be done in an appropriate way. From the lighthouse preservation handbook, these are guidelines for cleaning historic masonry lighthouses:
- Clean masonry only when necessary to halt deterioration or when heavy soiling must be removed to prevent damage to the masonry.
- Carry out masonry surface cleaning tests after it has been determined that such cleaning is necessary. Do not clean masonry merely to improve appearance.
- Clean masonry surfaces with the gentlest method possible, such as using low pressure water and detergents and natural bristle brushes. To select the gentlest method possible, tests should cover a period of time sufficient to determine both the immediate and long-range effects.
- Always allow for thorough drying time of the masonry (months or possibly years) before proceeding with any sealing of the exterior or interior.
- Always neutralize any chemical treatment.
- Do not sandblast brick or stone surfaces using dry or wet grit or other abrasives. These methods of cleaning permanently erode the surface of the material and greatly accelerate deterioration.
- Do not use a cleaning method that involves water or liquid chemical solutions when there is any possibility of freezing temperatures.
- Do not clean with chemical products that will damage masonry, such as using acid on limestone or marble or leaving chemicals on masonry surfaces.
- Do not apply high-pressure water-cleaning methods that will damage historic masonry and the mortar joints.
Tough guidelines, huh? But if we want our lighthouses to be here for generations to come, we must follow them. Or like the Healer’s oath…First, Do no harm.
More About Restoration Challenges
- Lighthouse Restoration Can Be a Challenge
- Lighthouses - Self Destructing Bricks
- New Technology For Renovating Historic Lighthouses