Exterior terra cotta ornaments

In Conservation DistList Instance: 11:72, February 24, 1998
Jane Tisdale <jtisdale [at] mailserv__mta__ca> requested info on
consolidating and cleaning exterior terra cotta ornaments.

I am somewhat familiar with Jahn products, although I have never specified
them.  However, I have seen them recommended in several technical articles
and discussed by qualified terra cotta consultants including 1) Jerry
Stockbridge with Wiss, Janney, Elstner Assoc. in Chicago 312-272-7400); 2)
Susan Tindall of Historic Restoration Services, Ltd. in Chicago; 3) Mary
Oehrlein in Washington, DC 202-387-8040).  However, you may want to
contact Michael Edison with Edison Coatings: Edison [at] compuserve__com for a
comparative product for terra cotta restoration.

The Landmarks Preservation Council of Illinois 312-922-1742) published a
wonderful study in 1984 called "Terra Cotta: Preservation of an Historic
Building Material", by Susan Tindall and Nancy Berryman.  You may want to
obtain a copy of this work.

    In the Landmarks Preservation Council's study, cleaning is
divided into three categories--mechanical, plain water, and
chemical.  Mechanical methods include high pressure water blasting
(over 500 p.s.i) and are not recommended for terra cotta because of
the potential for glaze damage. Plain water techniques include steam
cleaning (1-1/2 gal/min. at 150 p.s.i to 5 gal/min. at 300 p.s.i.)
and the use of a sprinkler hose system running for 24 to 100 hours.
These methods should be considered only on watertight, mildly dirty
terra cotta.  Chemical methods are complicated and require precise
testing before specifying.  A lot of damage can be done with
improper use of chemical cleaners.  This is where consultation with
an architectural conservator who is experienced with terra cotta may
be required.

John Horton, Restoration Specialist
NC State Historic Preservation Office

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                  Conservation DistList Instance 11:74
                   Distributed: Friday, March 6, 1998
                       Message Id: cdl-11-74-003
                                  ***