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Subject: Limestone


From: John Horton <john.horton>
Date: Wednesday, May 9, 2001
Frenkie Chetcuti <mozart [at] global__net__mt> writes

>I would like some information on how to remove the black crust which
>formulates on limestone, either mechanical or chemical cleaning.
>Both are of interest to me.

Historic preservation standards highly recommend that the most
gentle means be used for cleaning masonry. In typical order of
preference:  water soaking, water washing, water washing with
detergents, steam/hot-pressurized water cleaning, chemical cleaning
and/or poulticing. Usually, abrasive mechanical methods are not
recommended due to the likelihood of damaging the stone. Depending
on the condition of the masonry, water cleaning methods can also do
damage. It is critical that systematic testing be done to determine
the least damaging method that is still effective. Do not try to aim
for 100% clean.

I would recommend as an excellent reference the National Park
Service's Preservation Brief #1: "Assessing Cleaning and
Water-Repellent Treatments for Historic Masonry Buildings" by Robert
C. Mack, FAIA and Anne Grimmer, (Washington, DC, November 2000).
This publication can be viewed online at

John Horton, RA
Restoration Specialist
NC State Historic Preservation Office
Western Office - Archives and History
1 Village Lane, Suite 3, Biltmore Village
Asheville, NC 28803
Fax: 828-274-6995

                  Conservation DistList Instance 14:61
                  Distributed: Thursday, May 10, 2001
                       Message Id: cdl-14-61-006
Received on Wednesday, 9 May, 2001

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