Black slime is attacking our national monuments and buildings ... and it's all our fault. The methods of building cleaning the last 30 years have created a difficult to remove biological soup on our buildings. Here is why we need to change our ways.
The original 1792 Maryland State House dome retains its original paint beneath 17 later coats. What is now a demure gray and white dome was once brilliantly golden -- just as it was recorded by Charles Willson Peale when he drew the color scheme while overseeing the installation of Benjamin Franklin's first lightning rod on a public building -- an element that also remains to this day on the building where the Treaty of Paris ending the Revolutionary War was signed with the British while Annapolis was the nation's capitol.
Preservation projects are nothing like new construction since there are unknowns. Because they are normally bid just like new construction, the surprises that arise later make preservation projects more expensive. Too often risk mitigation on restoration projects means increasing the budget 50% or more. This isn't necessary. By reserving the first month of the project for on-the-scaffold investigations by the conservators with the key members of each team of tradesmen, optimal details can be developed and any training needed to show tradesmen new skills can occur before contractors finalize their bids for the project.
As this 1917 military structure was re-purposed into offices, the wood graining of the formwork for the concrete pours was repaired with grout and faux bois graining tools and the surfaces were casein painted in a tone that matched the reaction of high pH lime from the original concrete pour attacking the oil from the formwork and the tannins in the wood, creating a visibly soft and inviting interior to a concrete and glass structure.
Using drones to inspect inaccessible areas on a routine basis or after storms is a prudent diagnostic technique we have been using since 2013 and should be part of annual historic site maintenance and any initial planning for projects. This post also touches on the use of gel disks to sample and determine types of staining material and the best non-destructive methods for remediation.
This is part of larger series on carbon fiber (CF). If you are just joining this blog now, please take a moment to review the previous carbon fiber repair posts. In initial attempts to determine which CF cloths and resins to use, we reviewed loads of technical literature. Too often though it was focused… Continue reading Carbon Fiber: From Woodwork to Masonry
Methods for carrying the load of deteriorated joist ends using carbon fiber "mittens", information about the carrying capacity increase with each ply of carbon fiber tape on a timber, and a means of extending timbers with grafted elements like glass after casting an acrylic tooth cap to fit the damaged end of a timber, all designed with the wide-ranging timber damage at the Menokin Ruin in mind, but applicable to many buildings for in-place supplemental strengthening.