THE CLEANING OF MARKERS OF HISTORICAL SIGNIFICANCE REQUIRE SPECIAL CONSIDERATION. IF THE MARKER YOU ARE ATTEMPTING TO CLEAN IS OLD OR APPEARS TO BE BRITTLE WE RECOMMEND YOU CONSULT AN EXPERT BEFORE ATTEMPTING TO CLEAN THE MARKER.
Pressure Washing of gravestones is a somewhat new and serious threat to cemeteries. A search of the internet will find hundreds of websites, all with a similar wrong message - "In most cases moss or most stains can be removed by pressure washing and professional cleaning". Most of these websites are for monument companies and seem to be making use of the same standard FAQ. One website goes so far as to imply that The Association for Gravestone Studies is aware and approves of the use of pressure washing for gravestones. However a quick glance of their website proves this not to be the case. Others still are for Cemetery Monument Restoration services - people that should know better than to use this method.
The National Center for Preservation Technology and Training (NCPTT) recently organized a seminar and workshop on the conservation of gravestones and other monuments commonly found in cemeteries. More than 60 participants from around the nation participated in the events held in Natchitoches, Louisiana. The participants represented a wide array of individuals involved in cemetery preservation, including cemetery association members, State Historic Preservation officers, national and state park employees, K-12 teachers who use cemeteries in their lessons, doctoral students con-ducting research in cemeteries, cemetery caretakers, monument builders, and family cemetery owners.
Following the conference, NCPTT held a two-day workshop including hands on condition assessment, safe handling procedures, and conservation treatments. The conservation treatments encompassed cleaning tests using water, hand scrubbing with soft-bristle brushes, chemical methods, and low-pressure washing (less than 600 psi).
The fact that they would recommend any type of pressure washing is of great concern. While this method may produce the desired results of a clean gravestone, Saving Graves is strongly opposed to the use of pressure washing. There is simply far too much risk to the stone using this method. Any water pressure over 40 psi has the potential to cause significant damage to a stone, depending on the condition of the stone. A standard home garden hose with a nozzle attached will put out on average about 50 psi and the nozzle may actually cause the stream to be more direct than the stone can handle. The use of a pressure washing system on a gravestone will not only remove the outer surface of the stone, but expose the softer interior pores. These newly exposed pores will have a tendency to catch and hold onto grime and moisture that travel through the atmosphere. Trapped moisture within the stone from pressure washing will lead to a shorter stone life. If used on older stones, pressure washing can and will flake off entire layers of old brittle stone.