My Covid Vacation Part 2: Biofilms and Masonry Repair

An update on biofilm clearing and masonry repairs work over the last few years

Udall stone 5 years clean

As we approach five years since our cleaning of this single stone on the Udall Building, it remains clean despite being below infected stones.

Photo taken 1/21/23. Cleaning completed 7/10/2018.

Our development of alternative biofilm lysing and clearing approaches for complex challenges has progressed at cemeteries and on sculptures during these last few years.Some of this work has required addressing biological growths trapped beneath waterproofing. Plus in this interlude we got our hands dirty again reminding Annapolis that masonry repairs really can be nearly invisible if you chose the right materials and techniques.

If you have not seen our earlier post describing how the current methods of building cleaning are creating the conditions for rapid re-soiling and biological infestation, please click here.

There have been many unsuccessful attempts to clean the Udall Building, plus there had been problems with excessive water use and water infiltration around the windows during earlier attempts so we offered to show we could quickly clear the stones using less water, avoid water infiltration, and ensure true clearing of the surface by offering to do a mockup. One of their legitimate questions was whether we could prove we had cleaned the surface in a manner to avoid rapid regrowth. And one of our questions was whether it might be possible that, despite a paucity of records, it might be possible that the difficulties in cleaning this building were possibly due to water-proofing having been put on in the 60s which was now breaking down and providing a substrate for the growths.

We will talk more about the specifics of our work to answer those two questions in an upcoming posting. During this Covid interlude we found opportunities to conduct additional cleaning tests of a newer process we have been developing to remove biological growths.

Again this is more than a challenge of soiling. The removal must addresses the multi-species biofilms that are increasingly infecting recently-cleaned buildings where quartenarian ammonium compounds, in the class of materials like Lysol, were used and residues of both these hydrophilic cleaning compounds and nutrient-rich soaps remain. This creation of a water-retaining and compost-like collection of carbon and nitrogen residues encourages complex colonization by both aerobic and anaerobic species of bacteria and fungi. These symbiotic communities allows components beneath to work protected from UV damage and in a continuously moist environment that rapidly mine the stone (increasing its surface area and thus its rate of weathering that much faster) while upper layers create a protective chitinous shell that is not easily breached.

Marble lion cleaning in progress

The cleaning challenges get even more interesting, when waterproofing has been added, because it provides a different kind of protection for bacteria to grow beneath, as well as on top of the waterproofing, with very different sorts of colonizes at each level, and the challenge of how to lift the waterproofing material itself to get to the biological materials beneath.

As these images show, it was a long process until these lions were cleaned and back in the truck bed headed for home. The waterproofing had been intended to protect them. Yet in fact it was holding water inside beneath it, leading to increasing destruction of the stone as seen by the many significant fissures that needed to be filled after cleaning and the chalky nature of the stone itself once the waterproofing was lifted. We consistently find as these colonies of bacteria and fungi thrive under a protective surface, they are able to mine and weaken the surface of the stone, and go after particular veins and occlusions in the stone, whether on artifacts or buildings.

One thing our cemetery work has made clear is that biological cleaning can be quite complex when we are trying to remove biological without burning off the surface of the stone. (Yes, acid cleaners are still the most popular way to clean even marbles and limestone, meaning defacing them by removing the upper layers of stone and losing detail with each passing “cleaning”). In some cases we found in cemeteries near industrial sites and rail yards were coated with bituminous substances that needed to be removed first. We began using NIR or near-infrared spectroscopy for field inspection of surfaces to determine if the top layer was predominantly biological or needed other interventions first. As we have been building our database of NIR scans, it is helping us also determine in advance if there are silane or siloxane waterproofing treatments that may need to be removed to get at growths beneath.

We have also come to understand that there is also a metallic component to many of these stone cleaning situations. Yes, the stones are metallic (calcium, iron, etc) but what we are finding is that the mining of the stone also relies often on siderophores or iron-chelating compounds secreted by bacteria and fungi as part of the symbiotic colonies. Therefore we often need to chemically break those iron bonds and chelate as part of the cleaning process.

Maryland Inn repointing

And finally, I helped a friend with masonry repairs to an 1830s office building in Annapolis, a city that seems to struggle to get good masonry work done.

This little brick office building suffers as many historic buildings with porous brickwork does from the heavy use of city-wide deicing salts. In this instance a pothole in the street had for years sent the winter’s salt-laden slush onto the building face and kept it consistently wet so that it had suffered from the salt and freezing damage.

Despite trying to first clean and poultice the base of the building to extract as much salt as possible from both the bricks and mortar, the faces were simply too damaged. Many bricks had already been reversed previously as well, meaning that replacement was the only practical solution. But the brick sizes were non-standard so what options did we have to get a good match?

I cannot recommend Lynda Evans at StoneArt in Church Hill TN enough. She can match any brick or terra cotta shape and texture and run large or small kiln batches for any size project.

But of course, bricks are only half the equation, and as the Maryland Inn makes clear, the wrong mortar, wrong mortar color, and inappropriate tooling of joints is equally disruptive the appearance of a building even with its original bricks still in place.

Mortar matching, ideally using local sand and properly tooling the joints to be recessed from the brick arris to create proper shadow lines is equally crucial to an “invisible” repair. Yes, the greatest compliment is not your work looks great but … so what did you do here??