Campbell Center Maintenance Workshop, Follow Up III. In June Bob Yapp and John Leeke taught a course on maintenance methods and materials for historic buildings. Many National Parks Service workers attended as well as others involved in caring for historic buildings. This video shows window sill decay stabilization. More about the Methods and Materials for Maintenance of Historic Buildings course: http://www.campbellcenter.org/pages/historic.html#maintenanceMore about the Campbell Center for Historic Preservation Studies: http://www.campbellcenter.org/index.htmlMore about John Leeke and Historic HomeWorks: http://www.historichomeworks.com/hhw/index.htmMore about Bob Yapp and Preservation Resources, Inc.: http://www.bobyapp.com/ Less