Why are you Cleaning?

The first question should always be, “does this stone truly need cleaning?” Often people mistake the patina of age for “dirt.” They want marble stones, for example, to be as white as when originally purchased – and this is a tragic mistake. Not only does such aggressive cleaning cause irreparable damage, but it destroys the stone’s patina – and history – making it look like the stone was placed in the cemetery only yesterday. Moreover, the cause of much biological growth is the shade created by the dense foliage of trees that usually can’t – or shouldn’t – be removed from the cemetery. Consequently, once you begin a program of washing you find that you must clean the stones every few months. And every cleaning, no matter how gentle, has the potential to cause additional damage to the stone.

So, you may decide that a soiled stone is best left in that condition.

There are times when biological growth may be causing deterioration of the stone. In such circumstances it may become necessary to clean the stone. Many professional conservators will also clean the stone in order to get closer to the original stone color for infill matching.

• Algae, lichen, fungi -- that may be green, black, gray, yellow, red, orange, brown, or blue -- can be hazardous to gravestones because they trap moisture on (and under the surface of) the stone. They also secrete acids that can dissolve limestone, marble, sandstone, concrete, and mortar. And they may insert their "roots" into the pores of the stone. These growths will swell and shrink in response to moisture, leading to cracking and spalling of the stone.

• Plant life -- such as ivy, ferns, and moss, may be hazardous to the gravestone because they have roots that will penetrate the stone and also because they trap moisture.

Removal of Organic Materials

On smooth, stable surfaces, algae, lichen, and fungus may sometimes be easily brushed or scraped off before washing (always use scrapers that are softer than the stone, such as wood popsicle sticks or bamboo skewers). Most surfaces, however, require wetting the growth before gently brushing, prying, or scraping them off the stone. Plants should be gently pulled out of cracks or clipped, and then the soil or debris they were rooted in should be brushed away from the stone. The plant's root system should be removed with the soil and debris. If there is a mass of plant life, don't just yank it from the stone -- you'll almost certainly damage the stone. Carefully clip or pull away each section, to prevent pulling away any loose or weakened fragments of stone.

4. Rinse the brush frequently! Use a clean brush to clean with; don't abrade the gravestone by dragging dirt, sand, particles of broken stone, twigs, etc. across the surface you are supposed to be protecting.

5. Use clean water. If the gravestone is particularly dirty, change your bucket of water frequently, so that you are not dipping your brush into a suspended solution of the grit and biological matter you are removing. This is another convenience of having water running over the stone throughout the cleaning.

6. Rinse the stone thoroughly with water.

Cleaning with D/2 Biological Solution

1. Thoroughly wet the stone with running water from a hose. This, of course, isn't necessary if this step follows basic water cleaning since the stone will ready be wet.

2. Heavy growth should be cleaned with undiluted D/2. For lighter deposits D/2 can be diluted with potable water from 1:1 to 1:4 parts water by volume.

6. Never undertake cleaning is freezing temperatures are anticipated within the next 24 hours.

Examples of Cleaning using D/2 Biological Solution

These photos show before (left) and after (right) cleaning of two granite monuments that had very heavy lichen growth.

This marble tab in socket stone was leveled, reset, and cleaned. The before photo is on the left; after is on the right.

What NEVER to do to Stone

There are some “cleaning” approaches that should NEVER be used on cemetery markers.

Use of bleach. Sodium hypochlorite (common bleach) contains salts that damage stone. Stone "cleaned" with bleach, upon careful inspection, reveals erosion and yellowing. Pool bleach (calcium hypochlorite) will cause identical problems.

Also be aware that many pool algaecides are very corrosive. Many may also be very damaging to the environment. We do not recommend the use of ANY such products. The only biocide that we recommend is D/2.

Use of acid cleaning. Acids on marble and limestone dissolve the stone, leaving an inappropriate glossy and crystallized looking surface. This damage cannot be undone and the use of acids is also dangerous to you and surrounding vegetation. 

Use of sand blasting. This approach (even if "soft" materials like glass spheres are used) is very harsh and will dramatically abrade the stone surface. This has the potential to actually accelerate further deterioration of the stone. Once done, there is no way to undo the extreme damage caused by sandblasting. The patina, or historical beauty of the stone, is entirely destroyed.

Use of high pressure water. Water pressure over 90 psi has the potential to significantly damage any stone that isn't sound, increasing spalling, and accelerating sugaring.

Recarving inscriptions. While not actually a cleaning technique, this is sometimes done to "improve" the readability of faint inscriptions. But it does irreparable damage to historic stones, destroying their original artistry and beauty -- and destroying the historic significance of the stone itself. There are other approaches if a family wants to ensure that the grave continues to be clearly marked, such as setting a new stone horizontal on the ground (such as the example to the left).

Sources for Products

Conservation   |   Working in Cemeteries   |   Conservation Ethics   |   Cemetery Forms   |   Lawn Maintenance   |   Cleaning

Resetting   |   Cemetery Ironwork   |   Stucco and Whitewash   |   Disaster Planning   |   Mortar and Brick