Cleaning Historic Masonry: Removal of Atmospheric Soiling, Stains, and Biological Growth
- Procedure code:
- GSA Historic Buildings Division
- Masonry Cleaning
- Last Modified:
Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
Part 1 – GENERAL
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- General Protection (Surface and Surrounding)
1.04 QUALITY ASSURANCE
Contractor shall submit to the Architect, GSA HP Staff or Project Team:
A detailed schedule of the areas to be cleaned, including an assessment of the problem surfaces, as well as proposed mockups and associated procedures, methods, products, and dwell times.
Once cleaning mockups are completed and approved by GSA HP Staff, Contractor shall submit proposed masonry cleaning procedures, application methods, dwell times, etc. for full scale project.
The manufacturer’s product literature for all proprietary cleaning products. Product literature shall include specification data, Safety Data Sheets (SDS), and instructions for storage, handling, and use.
A project safety plan to include at minimum: any personal protective equipment to be used by the contractor staff such as disposable clothing, gloves and safety glasses, procedures for emergencies and accidents, documentation of staff training in use of equipment and/or chemical products as required by the manufacturers.
The Contractor, at inconspicuous locations designated by the GSA HP Staff, shall prepare test panels using the appropriate cleaning methods, to determine the best method. The "best method" shall be defined as that which successfully cleans the masonry with no, or minimal, damage to the masonry substrate.
Size of test panels shall be determined by the GSA HP Staff or Project team.
The methods used, their application, etc. shall be in accordance with manufacturer's instructions and shall duplicate those procedures proposed for the overall masonry cleaning process. The GSA HP Staff shall conduct a thorough evaluation of each method after masonry cleaning is complete, to determine the best method for the overall work.
The testing shall include an evaluation of the materials and techniques proposed for the protection of surrounding areas from the chemicals used to clean the masonry. Evaluation must include the method to be used to collect the cleaning effluent.
Methods and materials for sealing cracks and openings prior to cleaning, shall be included in the mockups and approved by the GSA HP Staff.
For proprietary cleaning systems, a representative of the cleaning materials manufacturer(s) shall be present during the preparation and execution of the test areas
Approved test panel(s) shall become part of the work and shall serve as the quality standard for all similar work.
1.07 DELIVERY, STORAGE, AND HANDLING (as applied to products and materials)
Any paint or coating required to be removed which has not been disclosed by the Government to contain lead, shall be tested for lead by the contractor. All paints or coatings testing positive shall be handled and disposed of as lead-based.
Contractor shall isolate the work area with cones, tape or similar means as possible for the duration of the project, to prevent unauthorized individuals from entering the immediate work are.
For any work required on elevated surfaces (4 feet or more above the ground) Contractor shall install and use any ladders, scaffolding or platforms in accordance with OSHA regulations (29 CFR Subpart M).
Contractor and sub-contractor employees shall wear all required and appropriate PPE while on site.
1.09 PROJECT / SITE CONDITIONS
The Contractor is responsible for protecting existing adjacent areas and materials during the execution of the work and shall provide all necessary protection and follow all necessary work procedures to avoid damage to existing material assemblies and vegetation not a part of the work of this Section.
At a minimum, Contractor shall:
Protect woodwork, glass, and metal adjacent to masonry areas to be cleaned, from overspray and possible chemical or water damage from cleaning operations. Cover all window openings with waterproof plastic to prevent leakage to the building interior. Through cracks shall be sealed.
Protect surrounding vegetation from runoff during cleaning operations.
Exterior masonry cleaning work areas should be accessed from the exterior only. Under no circumstances are hoses to be run or equipment transported through the building during exterior masonry cleaning operations.
If necessary, Contractor shall erect waterproof enclosures around areas where cleaning operations are in progress to protect nearby property and passers-by from overspray of cleaning chemicals or rinse water.
If applicable, Contractor shall coordinate masonry cleaning operations with the other trades involved in exterior and interior restoration work, including but not limited to masonry restoration, sealing, and painting. Masonry cleaning is to be completed prior to restoration of windows, doors, and metalwork, and prior to any exterior painting in the affected areas.
All Contractor personnel performing masonry cleaning operations shall be provided by the Contractor with gloves, respirators, protective clothing and any other personal protective equipment (PPE) as recommended by the manufacturer of the masonry cleaning products and required by local, state, and Federal regulations.
Contractor shall complete installation of temporary sealants at window and door perimeters prior to starting cleaning operations where required to prevent leakage to the interior.
PART 2 – PRODUCTS
2.01 MASONRY CLEANING OF ATMOSPHERIC SOILING
- The method of cleaning and the level of clean shall be approved by the GSA HP Staff. Contractor shall protect adjacent materials, installed non masonry materials, and openings.
- Cleaning shall be undertaken through the mildest, least abrasive method as per testing.
2.02 CLEANING METHODS
- Water washing: Washing the surface with low jet pressure, not to exceed 300 pounds per square inch (psi), for water soluble dirt and chemical compounds, psi is to be determined during mockup with GSA HP Staff approval, lowest possible pressure will be used to achieve desired results. Optimal water pressure and wand distance are to be determined during execution of cleaning test patches. Note that most commercial pressure washing systems operate at significantly higher pressures than those recommended. Use of a pressure regulator to reduce pressures may be needed.
- Nebulous Sprays: Application of intermittent mist spray under low pressure to dampen surface. Optimal water pressure, time cycles, and duration of the cleaning technique are to be determined during execution of cleaning test patches.
- Detergents: Formulations made with dilutions of cleansers, surfactants, and chelating agents in water. pH Neutral or non-ionic detergents or surfactants are added to water for use on hydrophobic stains.
- Masonry Cleaners: Proprietary cleaning solutions containing detergents, acidic or alkaline compounds. If this type of product is proposed, great care must be exercised in product selection and preparation of test panels to identify potentially detrimental effects on the masonry and surrounding surfaces. Raw acids and/or alkalis may not be used for masonry cleaning.
- Poultices: A paste or slurry made with absorbent material or powder-inert clay, such as kaolin or sepiolite, diatomaceous earth (fuller’s earth); or Cellulose products such as pulp cellulose, shredded paper that is mixed with a cleaning solution (a liquid reagent such as water, organic solvent, among others).
- Water used for cleaning of historic masonry cleaning shall be potable and free of injurious amounts of oil, soluble salts, alkali, acids, and other impurities that might stain or otherwise damage masonry, use of an in-line water filter may be necessary.
- Off-the-shelf chemical masonry cleaners as tested and approved or approved equivalent product.
- Clean, potable water to remove chemical residue.
- Phenolphthalein or pH testing strips: Used to test pH of a surface after cleaning masonry with chemicals.
- Appropriate neutralizer as specified in masonry cleaner product information.
2.03 EQUIPMENT FOR MASONRY CLEANING
Soft natural bristle brushes shall be used for scrubbing. Metal bristle brushes and brushes with metal ferrules are not to be used.
Hoses, fittings, and equipment to be used for application of proprietary cleaning compounds shall be solvent, acid, or alkali-resistant as recommended by the manufacturer of the cleaning products.
Buckets, trowels, and other tools, to be used for mixing, storing and application of poultices, shall be solvent-resistant plastic. Wood scrapers and trowels are permitted. No metal tools or containers are to be used.
Water/rinsing method: Surfaces shall be rinsed with water after cleaning. Rinsing shall be undertaken until pH strips indicate that the rinse water and masonry surface have been neutralized. Rinse water will be collected and disposed of in accordance with Federal, State, and Local environmental standards. Rates of water pressure should start at 100 psi or below and shall be no higher than 400 psi with minimal saturation, psi is as determined during mockup and approved by GSA HP Staff, lowest possible pressure will be used to achieve desired results.
- SURFACES MUST BE FULLY NEUTRALIZED FOLLOWING CLEANING. Contractor must test pH levels of masonry to ensure neutralization.
2.04 MASONRY CLEANING OF STAINS
Contractor shall choose the gentlest method possible to remove the stain without damaging the substrate.
Contractor shall conduct masonry cleaning test patches, no greater than 6 inches by 6 inches, in discrete locations, as determined by the GSA HP Staff. The test patches will determine the gentlest, most successful method of removing the stains.
The method and level of “clean” shall be approved by the GSA HP Staff.
- Contractor shall conduct masonry cleaning of biological growth and/or bird dropping patches, no greater than 6 inches by 6 inches, in discrete locations, as determined by the GSA HP Staff. The test patches will determine the gentlest, most successful method of removing the stains.
- The method and level of “clean” shall be approved by the GSA HP Staff.
- Treat areas of algae/moss growth with an antifungal agent prior to general masonry cleaning.
Part 3 – EXECUTION
- The cleaning test patches shall be performed by the Contractor and reviewed by the GSA HP Staff, to determine the mildest successful cleaning method.
- Contractor shall submit testing and cleaning schedules, including approved methods and materials.
Contractor shall protect all adjacent materials and landscaping from chemicals and chemical runoff.
Runoff and waste from cleaning will be collected and treated according to local, state and Federal regulations, as applicable
Contractor shall remove and store light fixtures, downspouts, and other appurtenances to ensure full access to wall surfaces, unless otherwise noted by the Architect, GSA HP Staff or Project Team. Anchor holes and penetrations from appurtenances must be temporarily filled with removable sealant or protected with cover plates.
Contractor shall remove climbing plants and plant debris from the masonry prior to cleaning. With the approval of the GSA HP Staff, invasive vines shall be cut close to the ground and allowed to wither and dry. Drying may take up to two weeks. Dry vines shall be carefully removed and the façade surface cleaned with a natural bristle brush prior to other treatments.
3.02 MASONRY CLEANING
- Surface Preparation for Cleaning
- Building shall be watertight prior to cleaning, through cracks and openings shall be sealed or covered, as used in the mockup and approved by the GSA HP Staff.
- Nebulous Spray Water Mist
- The sprayer should be designed for the job. Sprayer shall include a timed shutoff valve for on/off cycling. Cycles can range from 3 seconds on and 40 seconds off to 4 hours on and 4 hours off for a period of 24 hours. Work should start from the top of the building and proceed downward. Natural bristle brushes can be used during misting.
- Chemical Cleaning
- Masonry surfaces are to be saturated with water prior to application of chemical cleaning products.
- Cleaning of masonry walls shall be performed from the bottom of the wall toward the top.
- Manufacturer’s specifications shall be followed for all products used.
- Contractor shall use natural fiber brushes or very low-pressure spray (not to exceed 100 psi) for product application, psi is as determined during mockup and approved by GSA HP Staff, lowest possible pressure will be used to achieve desired results. High-pressure spray equipment shall not be used for the application of any cleaning product.
- Soft natural bristle brushes may be used to agitate the cleaning product.
- Following product dwell, loosened soiling shall be removed using a low-pressure water rinse. Do not allow the cleaning products to dry on masonry surfaces, or to dwell beneath scaffolding or other access or temporary protection supports. Rinse surfaces from top to bottom using a 45 degree fan-tip nozzle with a nozzle pressure not to exceed 400 psi and a flow of approximately 4 gpm. Psi is as determined during mockup and approved by GSA HP Staff, lowest possible pressure will be used to achieve desired results. A minimum distance of 18 inches between the nozzle tip and the masonry surface shall be maintained.
- SURFACES MUST BE FULLY NEUTRALIZED FOLLOWING CLEANING. Contractor must test pH levels of masonry to ensure neutralization.
- Following cleaning. Contractor shall remove all temporary protection and inspect all areas for cleaning related damage.
- Removal of Algal Growth, Moss, and Bird Droppings (Biological Staining)
- Living plants must be killed and allowed to dry prior to removal from masonry surfaces.
- The Contractor may apply a biocidal product such as a quaternary ammonium product to colonies of moss, or other biological contaminants. After at least 24 hours, the Contractor may remove colonies of moss, loose growth, and accumulations of bird droppings from masonry surfaces to be cleaned using wooden scrapers.
- Contractor shall apply selected cleaning agent in accordance with manufacturer’s instructions and approved test panel.
- Following required dwell time, agitate with a soft bristle brush to lift and remove embedded growth. Contractor shall rinse surfaces from top to bottom using a 45 degree fan-tip nozzle with a nozzle pressure not to exceed 400 psi and a flow of approximately 4 gpm. Psi is as determined during mockup and approved by GSA HP Staff, lowest possible pressure will be used to achieve desired results. A minimum distance of 18 inches between the nozzle tip and the masonry surface shall be maintained.
- Heavily soiled areas may be spot cleaned as needed.
- Spot cleaning may be performed no sooner than 2 weeks after general cleaning has been completed
- Surfaces shall be thoroughly wet prior to application of spot cleaner. Apply approved product using a synthetic brush, roller or low-pressure spray and allow to dwell, but not dry, on surface. Dwell time to be in accordance with approved test panel.
- Following completed dwell time, rinse surfaces from top to bottom using a 45 degree fan-tip nozzle with a nozzle pressure not to exceed 400 psi and a flow of approximately 4 gpm. Psi is as determined during mockup and approved by GSA HP Staff, lowest possible pressure will be used to achieve desired results. A minimum distance of 18 inches between the nozzle tip and the masonry surface shall be maintained.
- Apply neutralizing rinse (if required) according to manufacturer’s instructions. Rinse from surface, bottom up, according to manufacturer’s instructions. Test pH levels of masonry to confirm neutralization.
3.03 FINAL REPORT
A. Contractor shall:
Provide a final report of completed work, including all approved submittals, mockups and photographs of the areas cleaned that were taken before, during, and after the work. Report shall also include:
- A written summary of the project.
- Results upon final inspection and approval.
- Discussion of steps taken or new findings not specified in the initial documentation.
- Any applicable ongoing care and warranty requirements.
END OF SECTION