Cleaning and Contamination Removal

Identify Contamination Before Selecting a Cleaner

Begin with Dry Removal

Remove loose debris before introducing water. Sweep, vacuum, scrape with approved non-damaging tools, and collect leaves, stones, loose granules, fasteners, metal filings, abandoned materials, dirt accumulations, and biological debris.

Dry removal reduces the amount of contaminated wash water and prevents debris from entering drains. Protect drain openings during cleaning without defeating emergency drainage or creating a flooding hazard.

Select the Least Aggressive Effective Method

Start with a small representative test area. Confirm that the cleaner and equipment remove the contamination without softening, swelling, etching, delaminating, discoloring, or puncturing the substrate.

1. Hand cleaning: Sponge, mop, soft-bristle brush, or approved pad for small or sensitive areas.
2. Detergent cleaning: Manufacturer-approved cleaner at the stated dilution, dwell time, agitation, and rinse procedure.
3. Pressure washing: Controlled pressure, nozzle, distance, angle, and travel speed suitable for the substrate.
4. Specialized degreasing or solvent cleaning: Used only when compatible, authorized, ventilated, and managed under applicable safety and environmental rules.
5. Mechanical preparation: Abrasion, grinding, scarifying, or other methods only when required for the substrate and approved system.

Oil, Grease, and Process Contamination

Kitchen exhaust, manufacturing emissions, hydraulic oil, compressor discharge, vehicle service, and maintenance spills may create contamination well beyond the visible stain. Determine the source and stop it before cleaning.

Use an approved degreaser and repeated wash-rinse cycles where required. Aggressive solvents can spread oil, soften roofing, create fire and exposure hazards, and leave residue.

AMPP SSPC-SP 1, Solvent Cleaning, is a recognized standard for removing visible oil, grease, soil, drawing and cutting compounds, and other soluble contaminants from metal before further preparation. It does not authorize an arbitrary solvent on nonmetal roofing.

If contamination has penetrated membrane, foam, insulation, facer, concrete, or a porous repair, removal and replacement may be more reliable than continued surface washing.

Biological Growth

Algae, mold-like growth, lichen, vegetation, and organic films require removal without damaging the roof. Correct the conditions supporting growth, including trapped debris, shade, leaking equipment, and persistent water.

Use only a treatment approved for the substrate and coating system. Protect workers, occupants, air intakes, metals, landscaping, and receiving water. A bleach solution permitted by one membrane manufacturer should not be assumed safe or effective for every roof material.

Chalk, Oxidation, and Weak Surface Layers

Weathered coatings and painted metal can develop a powdery surface. Washing may remove loose chalk but leave a weak boundary layer. After cleaning and drying, wipe or rub the surface with a clean contrasting cloth and inspect for transferable residue.

If chalk remains, repeat cleaning or use the specified mechanical preparation and stabilizing primer. Primer should not be used to glue down dirt or rescue an unsound coating unless the system manufacturer has evaluated the condition and provided written instructions.

Soluble Salts and Industrial Fallout

Coastal salt, cooling-tower drift, fertilizer, combustion residue, and industrial emissions may be water-soluble yet invisible after drying. Their presence can contribute to underfilm corrosion, osmotic blistering, and loss of adhesion.

Where exposure suggests a risk, the specification should identify the sampling method, locations, frequency, units, and acceptance limits. Do not invent a universal salt limit for every roof chemistry. Use the coating manufacturer's criteria or project-specific direction from the qualified designer.

Silicone Contamination Requires Special Attention

Silicone sealants, overspray, lubricants, and existing silicone coatings can create severe adhesion problems. Silicone may be difficult to see, and residue can spread during wiping or washing.

Identify the material, remove unsound silicone and contamination using the approved procedure, and use only a coating or primer specifically accepted for the remaining surface. Adhesion testing should represent the cleaned silicone-affected area. Do not assume that a strong coating will adhere to unidentified silicone residue.

Wastewater and Environmental Control

Roof wash water may carry sediment, oils, metals, cleaning chemicals, biological material, paint or coating debris, and other pollutants. A roof drain often discharges to a storm sewer or directly to the environment—not to a wastewater-treatment system.

• Identify every drain and discharge point before washing.
• Determine federal, state, local, owner, and site permit requirements.
• Use approved drain protection, filtration, containment, vacuum recovery, or collection methods.
• Do not discharge contaminated wash water to a storm drain merely because the cleaner is labeled biodegradable.
• Characterize, transport, and dispose of recovered liquids and solids as required.
• Protect landscaping, vehicles, walls, pedestrians, neighboring property, and occupied areas.

EPA's NPDES stormwater information explains that runoff can collect chemicals, oils, dirt, and other pollutants and that regulated operators may require permits and best management practices. Local requirements may be more specific.

Drying After Cleaning

A surface that looks dry may retain water in seams, fastener cups, reinforcement, porous concrete, granulated membranes, foam cells, facer edges, cracks, and low areas. Allow sufficient drying time for the substrate and weather conditions.

Verify dryness using the manufacturer-approved procedure. Reinspect after overnight dew, fog, rain, condensate discharge, or temperature changes. Never apply primer or coating over frost, condensation, visible moisture, or moisture exceeding the specified limit.

Cleanliness Acceptance Hold Point

1. The roof substrate and all prior repair materials have been positively identified.
2. Contaminant sources have been stopped or controlled.
3. Loose debris, dirt, chalk, oil, grease, biological growth, salts, and incompatible residue have been removed to the specified condition.
4. Seams, flashings, coating, foam, and other roofing components were not damaged during cleaning.
5. Cleaning agents and loosened contamination have been completely rinsed or removed.
6. Wastewater and debris were contained and disposed of properly.
7. The substrate is dry and within the specified moisture limit.
8. Previously cleaned areas have not been recontaminated by traffic, equipment, exhaust, dust, or runoff.
9. Representative adhesion testing or primer trials are ready to proceed.

Technical References

• GAF Liquid-Applied Roofing Manual, Version 2.2—Cleaning, damaged-substrate treatment, substrate-specific preparation, primer selection, and adhesion-testing guidance.
• Sika Technical Bulletin 17-03, Roof Surface Cleaning Techniques—Membrane-cleaning methods and precautions concerning abrasion, pressure, nozzle pattern, wand distance, seam direction, and runoff.
• AMPP SSPC-SP 1, Solvent Cleaning—Recognized metal-surface preparation standard for removing oil, grease, soil, and other soluble contaminants.
• U.S. EPA NPDES Stormwater Program—Information about stormwater pollutants, permits, and best management practices.
• NRCA Guidelines for Roof Coatings, updated 2026—Preparation, application, existing-roof, and quality-control guidance.

Application rule: Follow the current project specification, roof-system manufacturer's cleaning and preparation instructions, product data sheets, safety data sheets, environmental permits, and locally applicable discharge requirements. Named products and manufacturers are educational examples, not endorsements.