Cleaning gravestones is controversial and there are diverging opinions about the best course of action. It is the author’s view
that in general the appearance of age on a gravestone is a perfectly normal part of a cemetery’s development. In fact, the appearance of age on what is, after all, a thing of antiquity, actually enhances its interest and charm. And most types of lichen are harmless to stone (except perhaps over a period of thousands of years),(10) and will grow back in a relatively short time anyway if they are removed. In short, why expect shiny white stones in a historic graveyard? That said, lichens and excessive build-up of grime sometimes under the inscriptions on stones difficult to read. If, in such cases, it is judged absolutely necessary that a stone be cleaned, caution should be exercised so that irreparable damage is not done. And anyone undertaking to clean a gravestone should  always remember that these are old stones and it is perfectly normal and acceptable – and even desirable – that they should look old. Don’t attempt to turn an old gravestone into one that was carved yesterday!

The following are a few basics that should be remembered if and when you are cleaning a gravestone:

TOOLS
Only use suitable tools. These include soft brushes with natural or nylon bristles, toothbrushes, sponges, and wood or plastic spatulas when more pressure is required. Absolutely never use wire brushes, scrapers or scouring pads. These can be  extremely damaging to the stone surface, and while the stone may end up looking “as good as new,” it will actually lose part of its surface along with the dirt and lichens.

IDENTIFYING STONES
Different types of stone require different types of treatment. Before cleaning a gravestone, be sure to identify what type of stone you are dealing with. In Quebec, a variety of stones were used in early cemeteries, and often the material chosen was a function of its availability in the area and the time period in which the gravestone was erected. Slate was commonly used for some of the earliest gravestones, particularly in the Eastern Townships, where a number of quarries were active. Soapstone, limestone and sandstone were also occasionally used. Marble, however, was much more common throughout the province. The stone most often used for gravestones over the last century or so was granite. Each of these stones has its own characteristics and each of these must be carefully considered before beginning any cleaning project.

CONDITION OF THE STONE
The condition of any gravestone should be assessed before any cleaning operation is performed. Gravestones that are flaking,
crumbling or corroding should not be cleaned. Even a very light cleaning can further damage such stones.

CLEANING
When cleaning a stone, be sure to thoroughly dry-brush the entire surface first. This will remove all loose material, such as grass and moss. Next, wet the stone thoroughly and scrub with an appropriate brush. Scrub in a random orbit to avoid eroding or streaking the stone. Rinse repeatedly. This will remove the loose external dirt. The next step (if deemed necessary) is to mix the cleaning solution appropriate to the particular type of stone (see below), apply it to the stone, and rinse  thoroughly. Do not expect miracles, and do not be disappointed if the result of the cleaning is not a shiny, new-looking gravestone! These are old stones and it is only natural that they should show some age.

CLEANING SOLUTIONS
The use of improper cleaning products may do irreparable damage to gravestones. Avoid using commercial soaps, such as Ivory. According to the Association of Gravestone Studies (AGS), commercial soaps are “rendered insoluble by calcium ions present in the masonry and hard water. They may also produce free alkali and fatty acid salts in masonry.” Nor are commercial household detergents advised. According to the AGS, these detergents are “generally chemically complex synthetic compounds that usually contain additives that may be detrimental to masonry” and “may cause the formation and deposition of detrimental soluble salts in masonry … detergents are by no means harmless; they may be chemically  aggressive.” In other words, if it produces soluble salts, it may lead to corrosion. Most acidic cleaning materials (e.g., hydrochloric or muriatic acid, phosphoric acid, and so on) are not recommended. Nor are alkaline cleaners such as sodium hydroxide (eg., Borax) and sodium hypochlorite (Clorox), since they too can lead to the formation of soluble salts.

On the other hand, non-ionic detergents (e.g. Photoflo, a product used in darkrooms or Orvus soap, available at animal feed stores) are recommended for use on slate, marble, limestone, sandstone and granite. They are “electrically neutral cleaning agents that do not contain or contribute to the formation of soluble salts.” Ammonia and hypochlorite are recommended for cleaning biological growth (lichens and algae) from light-coloured stones (e.g., marble or limestone). Plain water is recommended for cleaning soapstone.(12)

POULTICES
To remove stains resulting from contact with iron, copper and bronze, efflorescence caused by the presence of soluble salts, or old paint that has been applied to gravestone inscriptions, a poultice (composed of fuller’s earth and other materials that will vary for each type of problem) may be applied.(13)

PRESSURE WASHING
Pressure washing is generally not recommended as a method for cleaning gravestones. Pressure that exceeds 90 psi can cause damage to early stones by removing the exterior layer of stone and exposing interior layers to the atmosphere (90 psi is less force than a garden hose with good pressure).

SANDBLASTING
Never sandblast gravestones. Sandblasting actually removes the exterior layer of stone and exposes the protected inside layers to the atmosphere, hastening deterioration. One can imagine the effect of repeated sandblasting treatments!

COMMERCIAL PRODUCTS
A number of commercial products, such as Klenztone and others, are now being marketed as appropriate for the cleaning of old gravestones. Again, caution should be exercised if employing one of these products. A manufacturer’s claim regarding a product’s effectiveness is one thing; the product’s long-term effect on a gravestone, the environment around it and human safety, is another thing altogether.

Jonathon Appell, a gravestone restorer with New England Cemetery Services, is of the opinion that Klenztone “seems to be quite toxic, and has warnings regarding killing grass and vegetation. It [also] has warnings regarding skin contact and pre-testing prior to use.” He adds, “I am not sure it’s harmful, but it is suspect. I would not use it without more information, and likely it is too harsh for historic gravestone cleaning at all.” He further cautions that the “cleaning of gravestones in general is not always advised, and can cause more damage than good.”(14)

That said, in cases where a gravestone is judged as appropriate lo clean, and depending on the kind of stone and the kind of staining, Appell suggests a product called D2, which is distributed (by mail) by Cathedral Stone Products in the U.S.  Appell says, is a biocide that kills biological growth on stone and masonry almost immediately upon application, and that penetrates into the interior of the stone to kill the growth beneath the surface. It has, he says, “been proven to be very effective to use on historic stonework of all kinds …D2 has become the product I personally use most of the time im the cleaning of stone.” (15)

In short, though we do not advocate the systematic cleaning of gravestones in this handbook, except perhaps in extreme cases, if cleaning absolutely must be done, then care should be taken to assess the type and condition of the stone, the amount of cleaning required, and the type of cleaning agents to be used. Investigate possible side-effects of products to be applied and seek independent advice if possible. Gravestones are there for the long-term, and immediate gratification now may cause more harm than good down the road.

REFERENCES

11) For information on identifying stone, see Tamara AnsonCartwright, editor, Landscapes of Memories: A Guide for  Conserving Historic Cemeteries, Repairing Tombstones, Ontario Ministry of Citizenship, Culture and Recreation, Toronto, 1998, 1-13.
12) Tracy Coffing and Fred Oakley, AGS Field Guide No. 4: Cleaning Masonry Burial Monuments, Association of Gravestone Studies, 2003; and Strangstad, 58-63.
13) For information on poultices, see Anson-Cartwright, 15-17.
14) Jonathan Appell, New England Cemetery Services, email correspondence to Matthew Farfan, January 20, 2008.