What is Biological Growth? A Guide to Removing Lichen, Mold, and Algae from Grave Markers
Cemeteries are places of peace, reflection, and remembrance. The headstones and monuments that stand there are enduring tributes to loved ones, crafted from stone meant to last for generations. Yet, if you look closely, you might notice a slow, silent transformation occurring on these markers. A greenish tint, a crusty patch of grey, or unsightly black spots on granite can begin to obscure the carved inscriptions and delicate details.
This isn't merely dirt or weathering; it’s a sign of life. The growth of lichen, mold, and algae on grave markers is a common issue, but one that, if left unchecked, can cause permanent damage. Understanding what these organisms are and how to safely address them is key to preserving these important historical and personal artifacts.
What Are These Growths? It’s More Than Just Dirt
The discoloration you see is a community of microorganisms, each with a different method of survival, all finding a home on the stone's surface.
Lichen on Headstones: Lichen is often the most tenacious growth. It’s not a single organism but a remarkable symbiotic partnership between a fungus and an alga (or cyanobacteria). The fungus provides the structure and protects the algae from the elements, while the algae, through photosynthesis, produces food for both. Lichens appear in various forms—crusty (crustose), leafy (foliose), or shrubby (fruticose). They attach themselves firmly to the stone surface with root-like structures called rhizines. This is why simply scrubbing them often fails; they are physically bonded to the stone.
Mold and Mildew: Mold is a type of fungus that thrives in damp, shaded conditions. On a grave marker, it often appears as a black, green, or pinkish slimy or powdery film. Unlike lichen, mold feeds on organic matter. While it might seem like stone has nothing to offer, decades of accumulated dust, pollen, and bird droppings provide more than enough nutrients for mold to flourish. Its thread-like structures (hyphae) can penetrate microscopic pores in the stone, leading to deterioration.
Algae: Algae are simple, photosynthetic organisms that appear as a green, slippery film. They are most prevalent in consistently damp and shaded areas. Algae themselves are not particularly destructive, but they create a moist environment that encourages the growth of more damaging lichen and mold. They also contribute to surface staining.
The Silent Damage: How Biological Growth Harms Stone
While these organisms may seem superficial, their long-term impact on grave markers is significant. The damage occurs through both physical and chemical processes.
Physical Damage (Biomechanical): As lichen and mold grow, their root-like structures penetrate the microscopic pores and fissures in the stone. As they expand and contract with changes in moisture and temperature, they act like tiny wedges, slowly prying the stone matrix apart. This process, over years, can lead to pitting, spalling (flaking), and a general weakening of the stone surface, which is especially damaging to delicate carvings and lettering.
Chemical Damage (Biochemical): All these organisms produce moisture and acidic byproducts. Lichens, in particular, secrete a variety of acids to help dissolve mineral nutrients from the stone. These acids—such as oxalic acid and carbonic acid—accelerate the weathering process, etching the stone and breaking down the bonds that hold it together. The dark pigmentation of some molds and lichens, especially the black spots on granite, can also absorb more solar heat, causing the stone to expand and contract at a different rate than the underlying layer, leading to stress and micro-fractures.
Moisture Retention: A blanket of biological growth acts like a sponge, holding moisture against the stone surface for prolonged periods. This constant dampness exacerbates both the physical and chemical damage and can lead to freeze-thaw cycles in colder climates, where trapped water freezes, expands, and cracks the stone from within.
Safe and Professional Methods for Removal
When you discover grave marker mold, lichen, or algae, the instinct might be to grab a wire brush and a powerful chemical cleaner. This is the single biggest mistake you can make. Abrasive tools and harsh chemicals will irreparably scratch, etch, and damage the stone, often accelerating its deterioration.
Professional conservators adhere to a "do no harm" philosophy, using the gentlest methods possible to achieve the desired result. Here is a breakdown of safe, professional-grade approaches:
1. The Gold Standard: D/2 Biological Solution
This is the product most widely used by professional cemetery conservators and national monuments services (like the National Park Service). D/2 is a proprietary, non-acidic, non-caustic cleaning agent specifically designed for removing biological growth from stone. It works by penetrating the organism and breaking down its cellular structure, after which the residue can be gently rinsed away. It requires no scrubbing, is safe for the environment when used as directed, and leaves no harmful residues.
2. Mechanical Removal: The Gentle Touch
For loose debris and some types of algae, gentle mechanical cleaning is the first step. The key word is gentle.
Tools: Use soft, natural-bristle brushes (like boar’s hair or nylon brushes). Never use metal brushes, scrapers, or power washers.
Technique: Agitation with a brush, combined with copious amounts of clean water, can remove a significant amount of surface growth. The water helps to lubricate and float away the particles without abrasive action. For very tenacious lichen, a wooden or plastic spatula may be used with extreme care to gently lift the edge.
The Dangers of Pressure Washing:
Using a pressure washer on a historic or modern grave marker is one of the most destructive actions you can take. The high-pressure stream forces water deep into the stone's pores and any existing micro-fractures. It can blast away the soft, weathered surface of the stone, erode delicate carvings, and permanently embed biological particles deeper into the surface. The result is often a prematurely aged, roughened, and more vulnerable stone.
A Note on Home Remedies:
You may find online recommendations for vinegar, bleach, or ammonia. Avoid these at all costs.
Vinegar (Acetic Acid): It will etch calcium-based stones like marble and limestone and can dull the finish on granite.
Bleach (Sodium Hypochlorite): It introduces harmful salts into the stone. These salts crystallize inside the pores, creating internal pressure that causes the stone to spall and crumble over time. It is also highly toxic to the surrounding environment.
Ammonia: Can cause discoloration and reacts poorly with many stone types.
A Final Word on Preservation and Respect
Caring for a grave marker is an act of love and respect. Whether you are a family member tending a recent plot or a volunteer in a historic cemetery, the goal is always preservation. The battle against lichen on headstones, grave marker mold, and algae is a slow one, fought with patience and the right knowledge.
Before attempting any cleaning, especially in a historic cemetery, it is always best to check with the cemetery management for any specific rules or regulations. For particularly valuable, historic, or fragile markers, the safest course of action is to consult a professional stone conservator.
By understanding the nature of biological growth and using only the gentlest, most appropriate methods, we can ensure that these silent sentinels of memory continue to stand with dignity and clarity for generations to come.