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.
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.
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.