National Resources

The National Center for PReservation Technology & Training is part of the National Parks Service. It's site has good up to date restoration information that should be consulted before any work is done on historic monuments. There are training videos as well as documents.
ncptt.nps.gov/category/training/cemetery-monument-conservation-materials-research/

Cleaning a Stone Grave Marker is a video by NCPTT Materials Conservator Jason Church.
http://ncptt.nps.gov/2007/cleaning-a-stone-grave-marker-2007-01/
An accompanying booklet can be found here.
ncptt.nps.gov/pdf/CMC-Cleaning-Booklet-EN.pdf

Here is a list of serveral more podcasts from NCPTT concerning cemetery and monument preservation and repair.

Stopping the Hands of Time" 9 Tips for Cemetery Preservation is a good overview for beginning the process of Cemetery Preservation.
ncptt.nps.gov/2007/stopping-the-hands-of-time-9-tips-for-cemetery-preservation/