PRO Team Mission Critical: Nissen Headstone Restoration

Historic Oakland Foundation’s Preservation, Restoration, and Operations (PRO) Team is an integral part of realizing the Foundation’s mission to preserve, restore, enhance, and share historic Oakland Cemetery. The goal of critical restoration is to identify fragile, dangerous, or visually intrusive monuments and walls and mitigate the problem before major damage occurs. This post offers a fascinating glimpse into how the team restored one of the cemetery’s oldest headstones.

James Nissen was Oakland Cemetery’s first official burial in 1850. His headstone, now 168 years old, has experienced a great deal of weathering and deterioration over the years: The inscription is entirely illegible, the marble surface is sugaring, and the stone has begun to delaminate (flake apart in sheets). Because of the stone’s extremely fragile state, the PRO team placed it on our “critical restoration” list for 2018.

After much research and consulting with experts in the field of stone conservation, we developed a treatment plan. Preservation Manager Ashley Shares, with the help of Preservation Specialist Sean Diaz, spent a week carefully conserving this special monument.

First, the soil around the stone was carefully loosened and the stone was removed and laid on wood planks. It was important to store the stone with enough support beneath it to keep pressure off any existing cracks and also high enough off the ground to keep it from getting damp.

Then, the stone was gently cleaned to remove harmful biological growth and surface staining. The intent here wasn’t to polish the stone to a brilliant white (to attempt to do so would badly damage the stone). Rather, we just wanted to remove anything on the surface. After the stone had dried overnight, we used a spray bottle to apply several coats of consolidant. A consolidant replaces deteriorated carbonate particles with silicon dioxide, allowing the stone to retain its original porosity and permeability.

The PRO Team hopes that the treatment will allow Nissen’s headstone to withstand the effects of time and weather far into the future.

Next, we used a hypodermic needle to inject the stone’s small cracks with a dispersed hydrated lime grout (DHL). DHL is a very ‘liquidy’ lime mortar without large particles of sand. Pilot holes were used to help the DHL deeply penetrate and fill the cracks. After the DHL cured, we used a fine mortar to fill the larger cracks along the side and top of Nissen’s headstone. We tinted the mortar with a small amount of black, mineral-based powder to closely mimic the color of the stone.

Finally, we carefully re-set the stone in its original location to ensure it was upright and aligned east-west. We gently tamped gravel and dirt around it. The PRO Team hopes that the treatment will allow Nissen’s headstone to withstand the effects of time and weather far into the future.

Projects like this headstone restoration are complex, time-consuming, and can become expensive, but they are necessary if we are to retain the historic character of Oakland Cemetery. Please help the PRO Team by donating to our critical restoration fund.