Surface Preparation by Roof Substrate

Preparation Has Five Objectives

1. Remove material that is loose, weak, contaminated, incompatible, or poorly bonded.
2. Produce the cleanliness and profile required for adhesion.
3. Preserve sound roof components without cutting, thinning, eroding, or driving water into the assembly.
4. Provide a dry, continuous surface capable of accepting the specified primer and membrane.
5. Create a documented condition that can be inspected and approved before coating.

Metal Roofs

Identify the metal and its finish: galvanized steel, Galvalume or aluminum-zinc-coated steel, aluminum, copper, stainless steel, factory-painted metal, field-applied coating, or another material. Preparation must account for corrosion, mill oil, passivation, factory finish, chalk, and dissimilar-metal conditions.

• Remove oil and grease before abrasive or mechanical preparation so contamination is not driven into the surface.
• Remove loose rust, mill scale, failed paint, chalk, and corrosion products to the specified standard.
• Feather sound coating edges and eliminate sharp projections and metal filings.
• Replace perforated or structurally weakened panels rather than covering them with coating.
• Prepare fasteners, laps, seams, flashings, gutters, and repairs as separate details.
• Apply the approved corrosion-inhibitive or bonding primer within the allowed time after preparation.

AMPP SSPC-SP 1 addresses solvent cleaning. AMPP SSPC-SP 2 addresses hand-tool cleaning, SSPC-SP 3 addresses power-tool cleaning, and SSPC-SP 15 addresses commercial-grade power-tool cleaning. The specification must name the required standard and any profile or intact-coating requirements. “Wire-brush the rust” is not a complete preparation specification.

TPO Membranes

TPO formulations and weathering conditions vary. New or relatively unweathered TPO may contain surface characteristics that make coating adhesion difficult. A system approved for aged TPO is not automatically approved for new TPO.

• Verify the membrane manufacturer, approximate age, formulation when available, and current coating-system eligibility.
• Repair open heat-welded seams, punctures, shrinkage, unsupported areas, and failed flashings before coating.
• Clean using the coating manufacturer's approved cleaner, concentration, agitation, rinse, and drying procedure.
• Use the specified TPO primer, activator, or surface treatment; do not substitute a general-purpose primer.
• Perform representative adhesion tests after full preparation and primer cure.

PVC and Other Thermoplastic Membranes

PVC surfaces may contain plasticizer-related films, accumulated dirt, biological growth, or repair materials that affect adhesion. Some older membranes become brittle, shrink, or lose surface integrity.

• Confirm that the exact liquid-applied system is approved for the membrane.
• Repair failed heat-welded seams and flashings with compatible membrane procedures where required.
• Use the specified cleaner and primer or surface treatment.
• Remove residue completely and protect the prepared surface from recontamination.
• Reject membranes that are too brittle, unstable, or deteriorated to support the restoration system.

EPDM Membranes

Aged EPDM commonly carries carbon-black residue, chalk, dirt, biological material, and remnants of seam adhesives or repair products. Correct preparation may require a dedicated EPDM cleaner or activator and extensive scrubbing and rinsing.

• Repair failed seams, shrinkage, bridging, punctures, termination defects, and deteriorated accessories.
• Remove loose talc, dirt, chalk, oils, and incompatible repair residue.
• Follow the complete scrub, dwell, rinse, and drying procedure for the specified system.
• Use the approved EPDM primer or activator at its stated coverage and recoat window.
• Test adhesion on representative field membrane, seams, patches, and repaired areas.

Built-Up and Polymer-Modified Bitumen Roofing

Asphaltic roofs may be smooth, granulated, aggregate-surfaced, aluminum-coated, previously coated, or heavily repaired. Preparation must produce a stable surface without exposing or damaging reinforcement.

• Remove loose aggregate, granules, dirt, biological growth, unstable flood coat, and poorly bonded repairs.
• Repair splits, blisters selected for repair, open laps, bare felts, flashings, and deteriorated edges.
• Evaluate soft asphalt, plastic cement, and incompatible mastics rather than burying them.
• Use an approved asphalt bleed-blocking primer where required; verify the number of coats and drying time.
• Account for roughness and granulation when determining primer and coating quantities.

Bleed-blocking primer can reduce staining or migration, but it does not stabilize a loose or saturated asphaltic roof.

Spray Polyurethane Foam

SPF must be sound, dry, securely bonded, and protected from degradation. Weathered foam can become powdery, friable, eroded, pitted, or moisture-damaged.

• Remove wet, contaminated, crushed, blistered, delaminated, friable, and UV-degraded foam to sound material.
• Rebuild deep defects with compatible roofing foam or the approved repair system—not field coating.
• Shape repairs to drain and remove sharp ridges, voids, and weak overspray texture.
• Use cleaning methods that do not saturate, tear, or erode the foam.
• Apply primer when required and coat prepared foam within the manufacturer's exposure limit.

Structural Concrete

Concrete preparation must remove laitance, curing compounds, form-release agents, sealers, oil, dirt, weak surface paste, and unsound material while creating the profile required by the liquid-applied system.

ASTM D4259-24 addresses concrete preparation by abrasion and is intended to create surface profile and remove foreign material and weak laitance. ICRI Guideline No. 310.2R-2013 uses Concrete Surface Profile comparators CSP 1 through CSP 10. The required CSP must come from the coating-system specification; one value does not apply to every roof membrane.

• Use approved grinding, shot blasting, abrasive blasting, scarifying, or other preparation methods.
• Prevent polishing, contamination, excessive aggregate exposure, and damage to reinforcement.
• Repair cracks, joints, spalls, voids, fins, honeycombing, and penetrations with compatible materials.
• Remove dust using industrial vacuuming and the specified final cleaning method.
• Verify substrate moisture, pH when required, surface tensile strength, and adhesion before application.

Cover Boards and Approved Board Substrates

Do not assume that every gypsum, cementitious, wood-fiber, polyisocyanurate, or glass-faced board can receive a liquid-applied membrane directly. The specific board, thickness, facer, attachment, joint design, and approved roof assembly must be confirmed.

• Replace wet, crushed, broken, swollen, delaminated, or facer-damaged boards.
• Correct unsupported edges, open joints, proud or overdriven fasteners, and uneven transitions.
• Keep boards dry and protected from weather before and during installation.
• Treat joints and fasteners using the listed or manufacturer-approved system detail.
• Use the required primer and reinforcement; do not improvise a direct-to-board assembly.

Existing Coatings

Existing acrylic, silicone, polyurethane, aluminum, asphaltic, or unknown coatings must be identified and evaluated for adhesion, compatibility, thickness, moisture, and widespread failure.

Preparation Matrix

Surface-Preparation Acceptance Hold Point

1. The substrate, existing coating, repair materials, and contaminants are identified.
2. Wet, loose, unsound, incompatible, and deteriorated material has been removed or corrected.
3. The required preparation standard, method, and profile have been achieved.
4. Dust, debris, oil, salts, cleaning residue, and abrasive have been removed.
5. The surface is dry and within specified moisture and environmental limits.
6. Seams, cracks, joints, fasteners, penetrations, drains, edges, and transitions are repaired.
7. The correct primer or activator has been applied within its coverage and recoat requirements.
8. Required adhesion tests, mockups, pull tests, or manufacturer inspections have passed.
9. Prepared work is protected from traffic, weather, condensation, exhaust, and recontamination.

Technical References

• GAF Liquid-Applied Roofing Manual, Version 2.2—Substrate-specific preparation for metal, SPF, TPO, PVC, EPDM, asphaltic roofing, concrete, and existing coatings.
• AMPP SSPC-SP 1, Solvent Cleaning—Removal of oil, grease, soil, and soluble contaminants before further metal preparation.
• AMPP SSPC-SP 2, Hand Tool Cleaning—Requirements for hand-tool preparation of steel.
• AMPP SSPC-SP 3, Power Tool Cleaning—Requirements for power-tool preparation of steel.
• AMPP SSPC-SP 15, Commercial Grade Power-Tool Cleaning—A more extensive power-tool cleanliness standard when specified.
• ASTM D4259-24—Standard Practice for Preparation of Concrete by Abrasion Prior to Coating Application.
• ICRI Guideline No. 310.2R-2013 overview—Concrete surface preparation selection and CSP 1 through CSP 10 comparators.

Application rule: The current project specification, approved roof-system manual, product data sheets, safety data sheets, substrate requirements, preparation standards, test results, and written warranty requirements control. Manufacturer examples are educational resources, not endorsements.