This PRESERVATION TECH NOTE was prepared by National Park Service. Charles E. Fisher, Technical Preservation Servies, National Park Service, serves as the Technical Coordinator for the PRESERVATION TECH NOTES. Special thanks go to Peter T. Flynn, Javier Salazar and Bernadette Sykes of Cannon and William Scott for their help in the writing of this Tech Note. Thanks also go to the following people who contributed to the production: Michael J. Auer, Brenda Siler, Kaye Simonson, and Theresa Robinson, Preservation Assistance Division, National Park Service, Cover Photo: Guaranty Building after 1980s Rehabilitation/Patricia Layman Bazelon. Kay D. Weeks serves as coordinator and designer for the PTN Online series.

All photos and drawings by the author, unless indicated.

PTN-24
September 2001

PRESERVATION TECH NOTES are designed to provide practical information on innovative techniques and practices for successfully maintaining and preserving cultural resources, All techniques and practices described herein conform to established National Park Service policies, procedures and standards. This Tech Note was prepared pursuant to the National Historic Preservation Act Amendments of 1980 which direct the Secretary of the Interior to develop and make available to government agencies and individuals information concerning professional methods and techniques for the preservation of historic properties.

Comments on the usefulness of this information are welcomed and should be sent to Chuck Fisher at the address below. This publication is not copyrighted and can be reproduced without penalty. Normal procedures for credit to the author and the National Park Service are appreciated.