Dangers of abrasive cleaning to historic buildings, undated

NYC 9/11 Public Portal Document

Preservation Brief 6: Dangers of Abrasive Cleaning to Historic Buildings Page 1 of 12

Preservation Brims Technical Preservation Services National Park Service

Dangers of Abrasive Cleaning to Historic Buildings Anne E. Grimmer

»What is Abrasive Cleaning? »Why Are Abrasive Cleaning Methods Used? ~ ',~• LVw

»Problems of Abrasive Cleaning »How Building Materials React to Abrasive Cleaning »When is Abrasive Cleaning Permissible? »Do Not Abrasively Clean These Historic Interiors »Mitigating the Effects of Abrasive Cleaning »Summary

"Chemical or physical treatments, such as sandblasting, that cause damage to historic materials shall not be used. The surface cleaning of structures, if appropriate, shall be undertaken using the gentlest means possible." The Secretary of the Interior's Standards for Rehabilitation.

Abrasive cleaning methods are responsible for causing a great deal of damage to historic building materials. To prevent indiscriminate use of these potentially harmful techniques, this brief has been prepared to explain abrasive cleaning methods, how they can be physically and aesthetically destructive to historic building materials, and why they generally are not acceptable preservation treatments for historic structures. There are alternative, less harsh means of cleaning and removing paint and stains from historic buildings. However, careful testing should precede general cleaning to assure that the method selected will not have an adverse effect on the building materials. A historic building is irreplaceable, and should be cleaned using only the "gentlest means possible" to best preserve it.

What is Abrasive Cleaning? Abrasive cleaning methods include all techniques that physically abrade the building surface to remove soils, discolorations or coatings. Such techniques involve the use of certain materials which impact or abrade the surface under pressure, or abrasive tools and equipment. Sand, because it is readily available, is probably the most commonly used type of grit material. However, any of the following materials may be substituted for sand, and all can be classified as abrasive substances: ground slag or volcanic ash, crushed (pulverized) walnut or almond shells, rice husks, ground corncobs, ground coconut shells, crushed eggshells, silica flour, synthetic particles, glass beads and micro-balloons. Even water under pressure can be an abrasive substance. Tools and equipment that are abrasive to historic building materials include wire brushes, rotary wheels, power sanding disks and belt sanders.

Abrasive cleaning can cause The use of water in combination with grit may also be classified as

http://www2.cr.nps.gov/tps/briefs/brief06.htm 03/05/2002 NYC-WTC 000093852