This specification describes the method which proved most successful in removing repellent gel from marble at the Tweed Courthouse. Relative success has been reported using similar materials and techniques at other historic buildings. Briefly, the cleaning sequence involves careful scraping to remove the bulk of the gel, followed by repeated applications of solvents applied in liquid and poultice form to remove the oily gel residue and staining.

The Tweed Courthouse study confirms that bird repellent gels cause serious damage to masonry. Retention of water resulting from the application of repellent gel to stone surfaces caused severe deterioration in marble window hoods saturated with the product. Because of the possibility of hidden stone damage, great care must be taken in applying and removing cleaning chemicals, particularly during poultice removal.

Instruct cleaning contractors to use a conservative rule of thumb: if evidence of deterioration raises doubts about the ability of the stone to withstand rinsing pressures and the mild abrasion of manual scrubbing and scraping, remove cleaning products as gently as possible and cease the cleaning procedure at that location.

In areas where the stone remains sound, each cleaning step may be repeated several times, as long as there is no evidence of masonry damage or discoloration resulting from cleaning products or procedures.

Because repellent gel products tend to get absorbed deeply into masonry pores, it may not be possible to remove all of the oily residue in areas where the masonry has been heavily saturated with gel. Be prepared to accept an improved, if not perfect, stone appearance.

Hire only experienced contractors who specialize in cleaning historic masonry buildings. Require contractors to demonstrate (with project descriptions, photographs, and references) successful experience in all specified cleaning techniques. Require specific experience in cleaning exterior masonry stains on historic buildings of similar complexity and similar materials (name all masonry types to be cleaned). See Preservation Notebook No. 3, "Bidder Competency Clause," for competency specifications, editing guidelines, and a checklist for evaluating bidder competency.

These specifications outline materials and methods for removing bird repellent gel only. Specifications for general cleaning and removal of other stains, if planned, must be added (consult the Building's Historic Structure Report, available in the GSA-NCR Technical Resources Library, 7th and D Streets, SW, Room, Washington, DC (202) 708-6278 for additional masonry cleaning specifications).

1-1 Description: Work in this section includes:

1. Removal of bird repellent gel from [LIST EACH TYPE OF STONE AND ELEMENT TO BE CLEANED]:
2. Protection of pedestrian and vehicular traffic, adjacent materials and buildings, and building occupants and contents from harm by cleaning operations.

1-2 Quality Assurance

1. GENERAL OBJECTIVE: The objectives of stone cleaning are to remove bird repellent gel [ADD OTHER TYPES OF SOILING INCLUDED IN THE SCOPE OF WORK FOR THIS CLEANING PROJECT, EG., GENERAL SOILING, COPPER STAINING, BITUMINOUS DEPOSITS. ALGAE] without damaging underlying material and to give the stone a clean uniform appearance. Protection of the stone form damage is the highest priority.
2. CONTRACTOR QUALIFICATIONS: This work must be done by a firm specializing in the cleaning of historic masonry. Refer to the Competency of Bidder Clause, Sections 00120 and 00900 for submission requirements.
3. In the event that the Contractor wishes to modify any cleaning method specified, he must submit his proposal in writing to the Contracting Officer's Representative (COR) for consideration. The COR may ask for test samples before approval. Approval or rejection of the Contractor's request will be at the COR's discretion. Any such changes shall be at no additional cost to the Government.

1-3 Regulatory Requirements

Comply with municipal and Federal regulations governing cleaning, chemical waste disposal, and scaffolding

1-4 Submittals

1. Protection Program: Prior to the execution of cleaning samples, submit to the Contracting Officer's Representative a written description of the methods and materials for protection of all surrounding materials not to be cleaned.
2. Waste Water Collection and Removal: Prior to execution of cleaning samples, submit to the Contracting Officer's Representative a written description of methods of waste water and chemical collection and removal.

3. Submit to the Contracting Officer's Representative in triplicate a written description of the methods, materials, and equipment proposed for use in cleaning each type of masonry specified. Submit actual samples of each cleaning product to be used, along with manufacturer certifications that chemical ingredients conform to those specified for each cleaning procedure.

1-5 Sample Cleaning Panels

1. Clean a representative sample of approximately 10 square feet of stone surface at locations selected by the Contracting Officer's Representative, for each type of stone to be cleaned and each different procedure to be performed, including scraping to remove gel bulk. The samples accepted by the Contracting Officer will be marked and left undisturbed to serve as standards for the entire job.
2. Sample cleaning procedures must be executed in the presence of the Contracting Officer's Representative and must demonstrate the Contractor's ability to perform each specified cleaning procedure without harming masonry. Damage to masonry as a result of cleaning operations may result in the technician's dismissal from the project.
3. Adjust cleaning materials and methodologies during test panel cleaning as directed by the Contracting Officer's Representative.
4. Allow a minimum of seven calendar days after completing cleaning samples to permit the Contracting Officer's Representative to study the sample panels for negative reactions.
5. Do not proceed with cleaning until cleaning samples have been approved in writing by the Contracting Officer.
6. Approved samples shall be marked and left unaltered for the duration of the project. Approved samples shall be used as the standard for similar work throughout the project.

1-6 Delivery, Storage and Handling

1. Deliver materials to the site in manufacture's original and unopened containers and packaging, bearing labels as to the type of material, brand name and manufacturer's name. Delivered materials shall be identical to tested materials.
2. Store materials off the ground in a clean, dry location. Remove materials which are damaged or otherwise not suitable for use from the job site.

1-7 Job Conditions

1. Take all precautions necessary to protect surrounding materials on the site, surfaces of the building not being cleaned. Adjacent buildings, pedestrians and vehicles from coming in contact with cleaning chemicals, overspray, or runoff.
2. Use polyethylene film, masking tape, and whatever means necessary to protect plantings, automobiles, building occupants, and building surfaces not being cleaned. Remove such coverings when masonry cleaning operations have been completed at that area of the building.
3. Repair or replace with new stock, at no cost to the Government, to the Contracting Officer's satisfaction, any materials or plantings damaged by scaffolding, laborers, cleaning materials, or cleaning operations.
4. Prior to full scale cleaning, perform, in the presence of the Contracting Officer's Representative, a site test of the protective methods to prove that chemical damage to stone, glass, interior finishes, and other surfaces not being cleaned will not occur.
5. Test all drains and other water removal systems to assure that they are functioning properly prior to initiating cleaning operations. Notify the Contracting Officer's Representative immediately of all blockages. Repair drains if so directed by the Contracting Officer's Representative. Do not begin cleaning until drains are in working order.
6. Provide a method to prevent solids such as stone or mortar residue from entering drains or drain lines. Clean out drains or drain lines that become blocked because of work performed under this Contract.
7. Follow manufacturer instructions regarding the safe storage and use of all products and equipment. Remove all solvents, soiled rags, applicators, and other flammable materials daily and dispose off- site according to Federal and municipal regulations.

1-8 Environmental Conditions

1. No cleaning shall be executed when air or masonry surface temperature is below 45 degrees F, unless adequate, approved means are provide for maintaining a 45 degree temperature of the air and materials during, and for 48 hours subsequent to, cleaning.