Attachment_9_-_Exhibit_G_Cleaning_of_Historic_Concrete.pdf

National Park Service

U.S. Department of the Interior

Golden Gate National Recreation Area

Division of Cultural Resources

Fort Mason, Building 201 San Francisco, CA 94123

Jason N. Hagin, (415) 561-4973 tel

(415) 440-2764 fax

Cleaning of Historic Concrete: General Requirements, Trial Cleaning and General Cleaning Procedures

General Requirements

The objectives of a general cleaning project on historic concrete surfaces will include:

1. Trial Cleaning (testing).

2. Revealing areas requiring replacement or repair.

3. Leaving the surface physically and chemically compatible for use and repairs.

4. Not causing physical or chemical damage to the historic concrete.

No general cleaning project on historic concrete shall commence prior to the approval of a Site Specific Health and Safety Plan and a formal determination on the absence of hazardous materials.

For historic concrete, the cleaning method utilized shall be bucket and brush method, a low pressure warm water spray, a detergent combined with a low pressure cold water spray or a combination of these methods.

When product samples are required for testing, these samples shall be provided in the manufacturer's original container with the manufacturer's original label which shall contain a description of the container's contents, recommended use and instructions for use, cautions and warnings and any additional safety labeling required for the use of the product.

Materials shall be delivered in manufacturer's original, unopened, protective packaging that plainly show the designated product name, manufacturer's directions and name of manufacturer.

Store materials in a dry place, off the ground and under cover to prevent damage and intrusion of water or foreign matter. The contractor shall provide and erect safe and adequate scaffolding and equipment required for the proper execution of the work. All scaffolding shall be properly braced and erected to insure the safety of the workmen and meet all appropriate OSHA regulations.

The contractor shall take all necessary precautions for the protection of all property and the safety of the public. The contractor shall provide, erect and maintain barricades, lights, danger signals, and warning signs as deemed appropriate by the Project Manager. All specified requirements shall be in addition to all of the approved manufacturer's requirements or recommendations.

Surrounding areas shall be protected from contact with detergents, rinsing and overspray. The surrounding areas shall include, but shall not be limited to: all adjacent surfaces and structures; all private property including automobiles, outdoor furniture, etc: all animal life and their habitat; all vegetation and plant life; and all other surfaces which would be adversely affected if placed in contact with the cleaning chemicals. The method and materials used for protection is subject to the approval of the Project Manager.

Water rinsing shall be confined to the work area by controlling the drift of water and spray.

Necessary screens, deflectors, tarpaulins and other protective measures shall be employed in order to confine the work and properly drain (or contain) waste water. All rinse water shall be clean, potable and free of materials injurious to historic concrete.

Check and follow all local and federal regulations on the disposal of construction waste and waste water.

Trial Cleaning (testing)

As in other types of cleaning tasks, cleaning historic concrete walls and flatwork requires testing procedures and a strict adherence to manufacturer's instructions. Before cleaning, it is beneficial to test potential cleaning procedures and solutions on a sample area of about 20 ft²

(2 m²), or large enough to evaluate the selected cleaning procedure.

Trial cleaning on larger projects not only serves as a means to determine whether stains can be removed, but helps to identify the most effective procedures that cause the least damage to the historic concrete. Optimal concentrations of cleaning products and unexpected problems can also be determined through trial cleaning. Once approved, the test area can serve as a standard for the appearance of the flatwork after cleaning.

Reactions between cleaning solutions and certain minerals found in some concrete may cause stains. It therefore is safer to test a small area before subjecting the entire project to the cleaning procedure. Ideally, a portion of the sample panel can be tested, leaving the resource and the rest of the sample panel undamaged in case the concrete is adversely affected. Where trial cleaning must be performed on an historic resource, select an inconspicuous location for the sample area.

Trial cleaning should be performed at temperature and humidity conditions that closel approximate the conditions that will be experienced during cleaning. Judge the effectiveness of a cleaning agent or procedure by inspecting the trial area after it has dried sufficiently, usually about 5 days. Approval of the trial area shall precede application to any additional areas.

Cleaning Procedures

Remove larger clumps of debris using bucket and brush, wooden paddles or nonmetallic tools. Metal tools may damage the concrete or leave behind fragments that oxidize and cause rust stains.

Select a proper cleaning solution. There are many types of proprietary cleaners available that are formulated to remove specific stains or for use with concrete. Be careful to select cleaning products suitable for concrete and adjacent materials and follow the cleaner manufacturer’s recommended instructions. Each product being considered should be evaluated as discussed previously under “Trial Cleaning.” Do not use unbuffered muriatic acid. Use of unbuffered muriatic acid solutions tend to cause further stains and damage concrete. Many proprietary cleaners contain acids, however, their formulations include other chemicals that make them safer, easier to use properly and more environmentally responsible. When selecting a cleaning solution, verify its compatibility with the equipment to be used. Mix proprietary cleaners in accordance with the manufacturer’s instructions.

Protect adjacent materials and nearby plants. Mask or otherwise protect windows, doors, and materials such as sealants, metal, glass, wood, limestone, cast stone, concrete and brick masonry and ornamental trim from cleaning solutions. Cleaning chemicals may also damage plants and grass. It may be necessary to prevent the cleaning solution and run-off from contacting plants or the surrounding soil, or collect it for proper disposal.

Saturate the area to be cleaned. For vertical surfaces, flush with water from the top down.

Saturated concrete will not absorb the cleaning solution or dissolved aggregate particles.

Areas below the area being cleaned should also be saturated and kept wet until after the final rinse to prevent streaking and absorption of the run-off from above. A maximum pressure of 30 to 50 psi (200 to 350 kPa) with a 25º to 50º fan- shaped nozzle is required when using a sprayer to presoak historic concrete.

Special care shall be taken during the cleaning operation in areas where historic features (including painted markings) may have deteriorated. Should any cleaning operation cause the slightest impact to the historic concrete, stop work immediately and notify the Project Manager.

Apply the cleaning solution. For proprietary compounds, follow the manufacturer’s instructions for application, dwell time and cleaning technique. Wooden paddles or other non-metallic tools may be used to remove stubborn particles. The cleaning solution shall be applied by a low-pressure sprayer, (30 to 50 psi [200 to 350 kPa]), with a 50º fan-shaped sprayer nozzle, or by brush. Cleaning solutions applied under high pressure can be driven into the concrete and become the source of future staining.

Rinse thoroughly. Use a 25º to 50º fan-shaped nozzle and a maximum water pressure of 200 to 300 psi (1,400 to 2,100 kPa) to flush the cleaning solution from the historic concrete. If trial cleaning or prior experience with the selected area has established that no damage will result, slightly greater (low) pressure may be used. Flush walls and flatwork with large amounts of clean water from top to bottom before cleaned surfaces can dry. Avoid water spray into large open cracks or open joints. The substrate shall be rinsed until the rinse water is neutral (pH7).

END OF MEMO