Overview of Masonry Cleaning Technologies

Procedure code:
GSA Historic Buildings Division
Masonry Cleaning
Last Modified:

This chart has been developed by a team of GSA architectural conservators and historical architects building on a matrix created by ICOMOS Intern Jong Hyun Lim for GSA in 2005, to supplement GSA Technical Procedures concerned with masonry cleaning.

GSA's Technical Procedures database includes specifications addressing a variety of conditions encountered in GSA projects, but does not provide a comprehensive selection of methods reflecting current technologies generally accepted among preservation practitioners. To place the individual technical procedures within the broader context of current practice, this chart offers an overview of current cleaning methods having potential relevance to GSA projects, with summary information on the intent, process, limitations, advantages, and disadvantages of each method listed in the chart.

Development of cleaning specifications always begins with a thorough examination of areas to be cleaned, followed by diagnostic analysis to ensure that the specifications address the building's particular materials and conditions and creation of plans for masking and other protective measures to prevent infiltration and damage to materials not being cleaned. Most buildings require a combination of cleaning approaches. Specifications must include testing provisions to determine which method(s) will be most effective without harming historic materials and to establish an agreed upon standard for expected results. Project recordation initiated prior to cleaning or undertaken as a first step in the cleaning process includes photo-documentation capturing the range of soiling conditions and cleaning test results. The approved cleaning test sample should remain exposed to view throughout the course of the project to ensure consistent results. Close out documentation, to be specified as part of the cleaning contractor's responsibilities and maintained in GSA's building files for future reference, includes project completion photographs and narrative documentation describing each cleaning method and product used.

GSA specifications must include technical qualification requirements and responsibilities for oversight of cleaning tests, building protection, and project execution by an architectural conservator specializing in historic masonry. Conservator oversight responsibilities must include resolution of unanticipated challenges that invariably occur in a large scale cleaning project. GSA specifications for historic building cleaning also include competency of restoration specialist requirements, to ensure the competency of firms and individual technicians engaged in historic material cleaning. Cleaning technician substitutions require the conservator's approval. Project set up and close out procedures to be included in the cleaning specifications include pH testing of dampened masonry surfaces before applying cleaning chemicals and after rinsing, to ensure against formation of salts within masonry units as a result of cleaning chemical residues left on the surface.

All GSA work affecting historic materials follows the Secretary of the Interiors Standards for Rehabilitation of Historic Buildings, along with technical guidance published by the National Park Service, the Association for Preservation Technology, the American Institute for Conservation, the International Council on Monuments and Sites, and other organizations dedicated to the advancement of technical knowledge in conformance with the Standards. Specifiers are expected to review available research and guidance to keep abreast of current practice.


Although federal acquisition regulations prohibit endorsement of specific products and firms, the GSA project team expresses its sincere thanks to individuals and organizations who contributed to this guidance with information on specialized procedures and proprietary processes.

We welcome reader corrections and information updates at historic.buildings@gsa.gov.

Caroline Alderson

Jong Hyun Lim

Tom McDowell

George Siekkinen

Mark Velsey

Bayard Whitmore

Special thanks to Roy Ingraffia, Director of Industry Development & Technical Services, International Masonry Institute, for peer review assistance.

Last Reviewed: 2017-08-13