Learn what's possible with the art and science of preserving our architectural past
Biofilm removal from on top of and below waterproofing layers on these marble lions exemplifies our work on cleaning sculptures, cemetery headstones, and doing cleaning mockups on buildings in a more sensitive and long-lasting manner than is typically used.
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.
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.
Site-built epoxy-impregnated carbon fiber allowed customized restraints to synch an earthquake-damaged tower and restrain lateral thrust in retaining walls, achieving a lot of stabilization within the limited funds remaining in a repointing project budget.
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
Mortar matching is often seen as difficult to do, but once you understand that historic mortars primarily came from local sources, one need only look to the local geology including at roadside cuts to recognize the aggregates of a sand in their former condition. This is the wonder of the fractal nature of stone reduced to sand. And often the sand you seek is right beneath your feet!
The basic idea behind determining the void space in a sand is to determine the ratio of lime needed to adequately bind the sand without pushing the sand grains apart. In other words, how to make the strongest possible mortar by optimizing the lime portion.
The right qualities of sand are crucial in lime mortar making and differ some from brickwork versus plaster and stucco. The increasing inclusion of crushed rock in sand mixes presents particular problems.
Google Maps for mortar matching?! Go local when seeking to match historic mortars as the sand you seek may well be under your feet. If you need to go off site, look nearby. When the mortar analysis checkbox is clicked by sending away for a report that does not give you an exactly matching source (without relying on tweaks from pigments that may not be stable and will change the lime-sand ratio of a mortar and its working properties), your money is being wasted and your building is not getting the best treatment.
The Preservation Science Blog 
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