How to Clean Lichen from Gravestones: A Preservationist’s Step-by-Step Guide
Lichen—a symbiotic organism of fungi and algae—adds a weathered, ancient aesthetic to cemeteries. However, for genealogists, conservators, and family historians, lichen growth on gravestones is more than an eyesore. It actively traps moisture, accelerates freeze-thaw cycles, and can chemically etch into stone surfaces, leading to irreversible erosion, delamination, and loss of inscription legibility.
Cleaning lichen improperly (e.g., using bleach, wire brushes, or pressure washers) causes vastly more damage than the lichen itself. This guide follows the standards of the Association for Gravestone Studies (AGS) and the National Center for Preservation Technology and Training (NCPTT).
Why Lichen Removal Is Necessary
| Problem | Effect on Stone | Long-Term Consequence |
|---|---|---|
| Moisture retention | Lichen holds water against stone for days after rain | Accelerated freeze-thaw spalling |
| Acid secretion | Lichen produces oxalic and lichenic acids | Dissolves calcite in marble/limestone; etches sandstone binders |
| Physical penetration | Rhizines (root-like structures) grow into pores | Mechanical prying of mineral grains |
| Biological staining | Pigments from algae and fungi | Permanent discoloration even after removal |
Critical warning: Never clean a gravestone if the surface is flaking, powdering, or shows signs of “crazing” (fine cracks). Consult a professional conservator first.
Stone Types and Their Sensitivity
Not all gravestones react the same way. Understanding your stone type dictates the cleaning method.
| Stone Type | Hardness | Acid Sensitivity | Recommended Cleaner | Forbidden Methods |
|---|---|---|---|---|
| Marble | Soft (3-4 Mohs) | Extremely high | Non-ionic surfactant (e.g., Orvus WA Paste) | Any acid, bleach, ammonia, pressure washer |
| Limestone | Soft to medium | Very high | Neutral pH stone cleaner | Wire brush, sandblasting |
| Sandstone | Variable (often soft) | Moderate | Water + soft brush (gentle) | Pressure > 300 psi, metal tools |
| Granite | Hard (6-7 Mohs) | Low | Biocides or D/2 Biological Solution | Acid (pitting risk), high heat |
| Slate | Medium | Low | Distilled water + soft nylon brush | Abrasive pads, strong alkalis |
Step 1: Pre-Cleaning Assessment & Documentation
Before touching the stone:
- Photograph the stone in raking light (light from the side) to highlight lichen textures.
- Perform a “tape test” – Press clear packing tape onto a lichen patch. If stone grains stick to the tape, do not clean – the surface is compromised.
- Check for historical designation – Some cemeteries require permits for any cleaning.
Step 2: Gather Approved Tools & Materials
| Tool | Purpose | Prohibited Substitute |
|---|---|---|
| Soft nylon brush (e.g., Whalebone brand) | Gentle agitation | Brass, steel, or stiff poly bristles |
| Wooden or plastic scraper | Lifting thick lichen | Metal putty knife |
| Garden sprayer (pump type) | Low-pressure water rinse | Pressure washer |
| D/2 Biological Solution | EPA-registered lichen/moss cleaner | Bleach, vinegar, or “wet & forget” |
| Orvus WA Paste | Gentle surfactant (marble/limestone) | Dish soap (contains salts and degreasers) |
| Distilled water | Rinsing (prevents mineral stains) | Hard tap water |
Step 3: The D/2 Biological Solution Method (Gold Standard)
For 90% of lichen-covered gravestones, D/2 is the non-toxic, pH-neutral, EPA-registered biocide that kills lichen without damaging stone.
Application Procedure
- Dry brush – Use a soft nylon brush to gently remove loose dirt, leaves, and surface lichen fragments. Do not scrub hard.
- Apply D/2 – Saturate the lichen thoroughly using a garden sprayer or soft brush. Do not dilute.
- Wait – Leave for 10–20 minutes. D/2 needs dwell time to penetrate lichen structure.
- Agitate lightly – With a soft brush and distilled water, gently scrub lichen areas. Lichen should slough off in sheets.
- Rinse – Use low-pressure water (a gentle hose flow, not jet) to wash away residue. Keep water running away from the stone base.
- Repeat – For thick crustose lichen (flat, crusty, gray/green), a second application 2–4 weeks later may be needed.
Why not bleach? Sodium hypochlorite (bleach) dissolves stone binders, leaves salt crystals that recrystallize inside pores, and only bleaches lichen white—it does not kill the fungal hyphae.
Step 4: Alternative Methods by Stone Type
If D/2 is unavailable, use this decision table.
| Stone | Lichen Type | Alternative Cleaner | Contact Time | Rinse Pressure (max) |
|---|---|---|---|---|
| Marble | Crustose (encrusted) | Orvus WA Paste (1 tbsp/gal water) | 5 min | 200 psi |
| Granite | Foliose (leafy) | Distilled water only | N/A | 400 psi (careful) |
| Sandstone | Fruticose (shrubby) | 50/50 distilled water + 70% isopropyl alcohol | 10 min | 150 psi |
Step 5: Mechanical Removal – When & How
Only for thick, peeling lichen on hard stones (granite, slate). Never on marble or friable sandstone.
- Wooden spatula – Insert under lichen edge at a 10° angle; lift gently.
- Plastic razor blade holder – Use only on granite. Scrape in direction of grain, never across.
- Soft-bristle toothbrush – For fine details around inscriptions.
Stop immediately if: You see stone powder, hear a gritty sound, or notice color change.
Step 6: Post-Cleaning Care
After cleaning:
- Rinse thoroughly – Residual biocide or surfactant attracts dirt.
- Allow to dry fully (24–48 hours) before reapplying any treatment.
- Do not seal – Never apply acrylic sealers, waxes, or “stone sealants.” They trap moisture and accelerate decay.
- Monitor annually – Light brushing once per year prevents lichen re-establishment.
Common Myths vs. Facts
| Myth | Fact |
|---|---|
| “Pressure washing is faster and safe if you stand back.” | Pressure washers erode inscriptions in seconds; even 500 psi can pit marble. |
| “Vinegar is natural and gentle.” | Acetic acid reacts with calcium carbonate (marble/limestone) to form calcium acetate—a water-soluble salt that leaches stone away. |
| “Bleach kills lichen permanently.” | Bleach only damages surface algae; fungal component regrows within months. |
| “You must remove every trace of lichen.” | Some lichen is superficial; removing it risks stone loss. Leave stable, non-acidic lichen on durable stone. |
When to Call a Professional Conservator
- Active flaking or powdering – The stone is in advanced decay.
- Historic markers pre-1800 – Fragile binders may disintegrate with any wet cleaning.
- Lichen covering >50% of inscription – Requires specialized poultice or laser cleaning.
- Any leaning, cracked, or sunken stone – Cleaning can destabilize it further.
Find accredited conservators via the American Institute for Conservation (AIC) or ICOMOS.
Final Checklist for Safe Lichen Removal
- Stone is sound (no flaking, powdering, or large cracks)
- Cemetery rules permit cleaning
- You have soft nylon brushes, distilled water, and D/2 or Orvus WA Paste
- No pressure washer, bleach, vinegar, ammonia, or wire brushes on site
- Weather forecast: dry, above 50°F (10°C), no rain for 48 hours
- You have before/during/after photos for documentation
Conclusion
Cleaning lichen from gravestones is an act of preservation, not restoration. The goal is legibility and slowing decay—not a “like-new” appearance. Using the D/2 biological method with low-pressure water and soft brushes, you can remove lichen safely on most marble, granite, limestone, and slate headstones. When in doubt, leave the lichen and consult a professional. Your restraint today preserves history for tomorrow.
