Safely Cleaning a Tombstone

Dear Donia,
How do you safely clean a tombstone?

Tombstones

Q. Dear Donia,

A local cemetery (listed on National Register of Historic Places) recently began offering power washing of tombstones/monuments.There are monuments and stone facades that are over 100 or 150 years old. While they believe the low power/no chemical/water only wash is safe, articles I have read indicate this may be incorrect. I would like to find an article/your response to give them which lists  best practices and methods to avoid. My concern is that once damaged, it's too late and the inscription may be lost or the stone irretrievably damaged. If this method is approved, great. If not, because they are so conscientious, professional and have such laudable leadership, I believe they will adopt any recommended methods or changes. Thanks, Karen

A. Dear Karen,

You are correct that any sort of power washing could be damaging to the stones. The National Center for Preservation Technology and Training has a great video on how to safely clean tombstones and in it they specifically state "Finally, we don’t want to use any harsh mechanical devices such as sand blasting, high pressured power washers, or power tools such as sanders or drills equipped with a wire brush. All of these methods can damage the grave marker." It is always best to exercise caution when cleaning since, once damaged, what is lost won't come back.
 
I hope this helps change the cemetery board's minds. Good luck, and please don't hesitate to contact us again if you have any further questions.