Historic preservation chemistry — what works on 19th-century masonry
Madison and surrounding Dane County hold dozens of churches built between the 1860s and the 1920s. The masonry on these buildings — soft Cream City brick, limestone from local Niagara Escarpment quarries, sandstone trim, and lime-mortar pointing — is structurally fragile in ways modern brick is not. A 3,000 PSI pressure wash that's perfectly safe on a 1995 office building will spall the surface off 1880s Cream City brick in a single pass and remove a generation of mortar that's irreplaceable. We do not run high-pressure equipment on any masonry older than 75 years. The chemistry we do use — D/2 Biological Solution by Sumner Laboratories — is the explicit National Park Service-recommended cleaner for historic stone preservation (referenced in NPS Preservation Brief 1 and Brief 6, the federal-standard guidance for cleaning historic masonry). D/2 sits on the surface, kills biological growth (lichen, algae, moss, black streaking from microbial mats) over a 2-to-8-week residency period, and rinses neutral. We brush-apply, dwell, and rinse at sub-500 PSI — the same protocol used on Gettysburg headstones, Statue of Liberty masonry, and historic graveyard markers across the country. Pressure-blasting on historic stone is what destroys these buildings. We don't do it.