Fax forwarding DEP briefing materials for Mayor's meeting, March 2002

NYC 9/11 Public Portal Document

Friday 15 of Mar 2002, Mayor Office ->718 595 4544 Page 23 of 29

to applications as dust or cleaning agents may enter building through openings in facades or fabric.

Cleanbig .Methods: The intent of these standards i.s to provide general guidelines for the removal of applied paint (or signage) from historic building exteriors that comply with the Secretaiy of the Interior's Standards for (he Treatment of Historic Properties. .-As mentioned above, masonry surfaces should be free of dust prior to implementing a removal program (see Performance Standards for Cleaning .y/asonry Exteriors).

The following information is explained in greater detail in Preservation Brief Number 38 ''Cleaning Graffiti from Historic .Masonry" by Martin E. Weaver;

Substrate Identification- Identification of the type of stone substrate will help determine the type of removal methods. Masonry materials can be categorized as being acid-sensitive. non-acid sensitis e, or alkali-sensitive. The application of inappropriate paint removers or cleaning agent.s can damage stone. .Acid-sensiti\'e materials include, but are not limited to: limestone, marble, trax'ertine, calcareous sandstones and shales; most polished stones; and glazed architectural temt cotta and brick. Non-acid sensitive materials include, but are not limited to: slate, granite, unglazed architectural temt cotta and unglazed brick. .Alkali- sensitive materials include, but are not limited to: glazed brick, glazed terra cotta, some granites, Indiana limestone, and many types of sandstone. Strong acid.s and strong alkalis can damage glazed and polished surfaces.

Removal with Water and Detergent- Water cleaning utilizes the application of a gentle, low- pressure. clean waler spray. Water alone can sometimes remo\-e paint. If the application of low-pressure waler is not successful in removing the applied paint, a neutral non-ionic detergent may he used in conjunction with a water application. .-Any detergent being used should first be tested in a small inconspicuous area prior to widespread application. The pressure of water applied to a masoniw surface should be carefully monitored (see ".Abrasive Removal”). Inappropriate detergents can cause permanent staining and damage to substrates

Removal using Poultices- Poultices are powdered materials (e.g. clay, paper, cellulose products, fidler's earth) that are mixed with water or a cleaning agent to form a paste that can be applied to a building surface. Poultices are often the most effective means of remox ing applied paint (signage) from masonry as they allow the cleaning solution to remain in place as long as possible, and draw out the staining material from the masonry. An experienced and qualified professional should apply poultices as improper application can sometimes draw out and redeposit stains on the opposite face of masonry surfaces. An\ cleaning application should be tested in an inconspicuous area or on mock-ups prior to widespread application.

Removal utilizing .Alkaline Compounds- .Alkaline compounds are typically used in poultices in the form of liquids (reagents), applied to markings/stains on non-alkali sensitive masonry. The application of alkaline compounds should be followed by a weak acid wash and a water

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