First, Do No Harm: A Field Guide to Cleaning Fragile Headstones

There’s a sandstone marker in our Section G for a Private Eames, who fell at Antietam. For fifty years, it was slowly disappearing under a blanket of dark algae and lichen, the inscription becoming a rumor. New grounds staff would often ask if we planned to clean it, to blast it back to its original state. My answer is always the same: first, we look. We put our hands on the problem, gently, and we assess. The most important work of cemetery headstone preservation happens before a single tool is picked up, in the quiet moment of deciding what to do — and what to leave alone.

Restoring delicate cemetery monuments is not about making them look new. It is an act of stewardship, a careful negotiation between the present and the past. A pressure washer and a bucket of bleach can scour a stone clean in minutes, and in doing so, strip away decades of its remaining life, leaving a porous, crumbling surface vulnerable to the next frost. Our duty is to stabilize, to conserve, and to gently reveal what time has obscured, not to erase its passage entirely.

Assessment Before Action

Not every headstone should be cleaned. The first tool is observation. Approach the stone and examine its condition. Is it granite, marble, slate, or a softer stone like sandstone or limestone? Granite can withstand more, but the historic markers that often need the most attention are made of far more delicate material.

Look for these warning signs:

• Flaking or Delamination: Is the stone peeling apart in layers, like pages of a damp book? If so, cleaning is out of the question. The priority is professional conservation to stabilize the stone.
• Sugaring: Gently run a hand over the surface. Does it feel sandy or granular, leaving a sugary dust on your fingers? This is common with marble and indicates the crystalline structure is breaking down. Aggressive cleaning will only accelerate this decay.
• Cracks and Fissures: Are there deep cracks? Water and cleaning agents can penetrate these, freeze, and wedge the stone apart.

If the stone seems stable but is simply covered in biological growth, you can proceed with care. But if you see any of the conditions above, the best course of action is to document the stone’s condition and consult a professional monument conservator. Sometimes, the most responsible act of grounds care is knowing when to walk away.

The Gentle Cleaning Toolkit

Your equipment should be simple and non-destructive. The goal is to remove surface growth without abrading the stone itself. Leave the hardware store solutions behind.

What to Use:

• Water: Clean, potable water is the primary tool. Use it liberally to saturate the stone before, during, and after cleaning. Distilled water is even better, as it contains no minerals that could leave deposits.
• Brushes: Only natural or soft nylon bristle brushes. Nothing metal. An assortment of sizes helps get into crevices.
• Scrapers: Wooden or plastic scrapers only. A popsicle stick can be surprisingly effective for carefully lifting lichen without scratching the stone.
• A Biological Cleaner: The professional standard is a product like D/2 Architectural Biocide. It is pH-neutral and works gently over time to kill algae, lichen, and mold without damaging the stone. Alternatively, a non-ionic soap (like Orvus WA Paste, available at agricultural supply stores) can be used, but it must be rinsed exhaustively.

What to Avoid, Always:

• Power Washers: The intense pressure drives water deep into the stone and can sheer off the surface, especially on sandstone and marble.
• Bleach or Household Cleaners: These are alkaline or acidic and contain salts that recrystallize inside the stone, causing it to spall and crumble from within.
• Wire Brushes: They will permanently scratch and gouge the surface of any stone.

A Step-by-Step Method for How to Clean Old Gravestones Safely

Let’s return to Private Eames’s marker. It’s sandstone, structurally sound but covered in a thick layer of black algae. Here is our process:

1. Saturate the Stone: Using a low-pressure sprayer or buckets, wet the entire headstone thoroughly with clean water. A wet stone is less likely to absorb the cleaning solution deep into its pores. Let the water soak in for several minutes.
2. Apply the Cleaner: Spray the D/2 solution over the entire surface and let it sit for 10-15 minutes. You may see the biological growth begin to change color. There is no need to scrub immediately.
3. Gentle Agitation: After the waiting period, use a soft bristle brush to gently scrub the stone. Work in small, circular motions from the bottom up. Working upwards prevents clean areas from being re-soiled by runoff and helps avoid streaking.
4. Rinse and Repeat: Rinse the stone thoroughly with clean water, again from the bottom up. If the stone is still very soiled, you can repeat the process. For thick, crusty lichen, you may need a wooden scraper to gently pry the main body off after it has been soaked and treated.
5. Be Patient: This is the hardest step. A biological cleaner like D/2 continues to work for weeks and months after application. The rain and sun will help it gently lift the remaining stains. The full result may not be visible for half a year. Document your work with photos so you can track the progress.

Our job is not to make the old look new, but to steward what has been entrusted to us, ensuring it can tell its story for another generation.

Developing a written policy for headstone cleaning and restoration can provide clear guidance for your staff and volunteers. It establishes a standard of care that honors the decedent and preserves the physical history of your grounds. The memory etched in stone is fragile. It deserves a careful hand.