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Last Updated: 09/22/2026

Commercial and Industrial Roof Coatings Certificate Program

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Commercial and Industrial Roof Coatings for Professional Roof Coaters

Silicone Roof-Coating Systems

Article 17 of 25

Silicone roof coatings are known for ultraviolet stability, weather resistance, flexibility, and resistance to prolonged water exposure. Those advantages do not make silicone a universal answer. Successful installation still requires a sound and dry roof, compatible preparation, substrate-specific primers, correct detailing, controlled film thickness, proper cure, and a plan for inspection, maintenance, and future recoating.

Silicone Is a Distinct Roof-Coating Chemistry

Silicone roof coatings are polymeric materials based primarily on silicone chemistry. Many commercial roof products are single-component, moisture-cured, high-solids coatings. Other formulations and system designs also exist, so the product’s current technical data sheet and complete manufacturer specification must control.

Silicone should not be confused with acrylic merely because both materials may be white, reflective, liquid-applied, seamless, and elastomeric. Silicone and acrylic differ in cure mechanism, water resistance, surface energy, dirt pickup, equipment cleaning, recoating, and compatibility.

Silicone is the chemistry. Elastomeric describes a performance characteristic. High solids describes formulation—not complete installed performance.

Why Silicone Is Used on Commercial Roofs

Properly selected and installed silicone systems may offer:

Strong resistance to ultraviolet exposure and weathering.
Resistance to prolonged water exposure when specifically approved by the manufacturer.
High solids by volume and substantial dry-film build.
Single-component application for many products.
Good flexibility across a wide service-temperature range.
Reflective white finishes with published solar-reflectance and thermal-emittance values.
A seamless, fully adhered field-applied surface.
Application over several approved roof substrates when properly prepared and primed.
Potential for future renewal using a compatible silicone system.

These are potential system advantages—not guarantees. The actual roof assembly, substrate, exposure, preparation, installed thickness, details, and maintenance determine performance.

Ponding-Water Resistance Does Not Correct Poor Drainage

Some silicone roof coatings are specifically represented as resistant to ponding water. This is a meaningful distinction from many water-based acrylic products, but it is frequently misunderstood.

Ponding-water resistance means that the named, properly cured silicone system has been approved by its manufacturer for the stated water exposure. It does not mean that:

Drainage defects can be ignored.
Wet insulation may remain in the roof.
Water can be trapped beneath the coating.
Structurally low or overloaded roof areas are acceptable.
Drains, scuppers, gutters, and downspouts no longer require maintenance.
Every silicone formulation carries the same approval or warranty.
Dirty standing water will not stain or foul the surface.

Positive drainage should still be provided wherever practical. Remaining ponding areas must be identified, documented, and accepted within the manufacturer’s written system and warranty requirements.

ASTM D6694/D6694M-25

ASTM D6694/D6694M-25 is titled Standard Specification for Liquid-Applied Silicone Coating Used in Spray Polyurethane Foam Roofing Systems.

Its scope addresses solvent-dispersed elastomeric silicone coating used as a protective membrane over spray polyurethane foam roofing. The principal polymer in the coating covered by the specification is predominantly silicone.

The Scope Matters

ASTM D6694/D6694M should not be presented as a universal application standard or blanket approval for every silicone coating, roof substrate, or roof assembly.

A product’s compliance with this material specification does not provide the substrate preparation, primer, detail construction, application rate, code listing, wind-uplift approval, fire classification, quality-control procedure, or warranty requirements for a complete project.

Silicone Material Properties

Property	Why It Matters	Contractor Caution
Solids by volume	Helps estimate the dry film remaining after cure.	High solids does not eliminate surface losses, profile allowances, or thickness verification.
Elongation	Indicates the film’s ability to stretch under stated test conditions.	It does not replace reinforced treatment of moving joints or unstable details.
Tensile strength	Indicates the stress the cured film can resist.	It must be considered with elongation, tear resistance, thickness, and aging.
Tear resistance	Helps indicate resistance to propagation of an existing defect.	Sharp edges, fasteners, traffic, and poorly terminated reinforcement remain hazards.
Hardness	Provides information about the firmness of the cured coating.	Hardness alone does not establish puncture resistance or walkability.
Permeance	Describes water-vapor transmission through the cured film.	It does not make a wet roof assembly suitable for coating.
Tack-free and cure time	Helps establish handling, recoating, weather exposure, and inspection timing.	Actual cure changes with temperature, humidity, thickness, and field conditions.
Solar reflectance	Indicates the fraction of solar energy reflected by the surface.	White silicone can lose reflectance as dirt accumulates.
Thermal emittance	Indicates the surface’s ability to release absorbed heat.	It does not establish waterproofing or whole-building energy performance.

High-Solids Silicone

High-solids silicone formulations contain a relatively large proportion of material that remains in the cured film. This may permit substantial dry-film build with fewer coats than some lower-solids products.

That does not mean every project can be completed with one coat. The manufacturer may require:

Separate primer or bleed-blocking primer.
Detail coats beneath the field coat.
Different or contrasting colors.
Two field coats for the specified system or warranty.
Additional material over rough, porous, granulated, or irregular surfaces.
Separate application passes to control pinholes, sags, bubbles, or holidays.

“One-coat capable” is not permission to disregard the named system specification.

Moisture Cure Does Not Mean Apply to a Wet Roof

Many silicone coatings use atmospheric moisture as part of their cure reaction. That fact is sometimes misinterpreted as permission to apply silicone over damp, wet, frosted, or contaminated surfaces.

A moisture-cured silicone still normally requires a clean, sound, and dry substrate. Liquid water, dew, condensation, frost, trapped roof moisture, or wet insulation can interfere with adhesion and system performance.

Temperature and humidity affect cure differently:

Low humidity may slow the cure of some moisture-cured silicones.
Higher humidity may accelerate surface cure.
Excessive thickness may cure at the surface before the full depth has developed its properties.
Cold temperatures may increase viscosity and slow cure.
Hot surfaces can change application behavior and reduce working time.

Measure ambient temperature, substrate temperature, relative humidity, dew point, wind, and surface moisture. Follow the current product-specific limits rather than relying on a general rule for silicone.

Approved Roof Substrates

Depending on the named manufacturer system, silicone coatings may be approved over:

Spray polyurethane foam.
Standing-seam and exposed-fastener metal roofing.
Modified-bitumen and built-up roof systems.
Concrete and approved cementitious surfaces.
EPDM, TPO, PVC, Hypalon, or other specifically approved membranes.
Existing compatible roof coatings.
Previously installed silicone roof systems.

The approval is usually conditional. Primer, cleaning, adhesion testing, moisture investigation, seam repair, bleed blocking, reinforcement, and minimum dry-film thickness may vary by substrate.

Substrate Preparation and Primer Selection

Substrate	Primary Concerns	Possible System Requirements
Spray polyurethane foam	UV degradation, exposed cells, blisters, wet foam, pinholes, surface texture, and damaged coating.	Foam repair, scarifying or cleaning, compatible primer where specified, and controlled coating thickness.
Metal roofing	Rust, loose coating, chalk, oil, fasteners, seams, panel movement, and dissimilar metals.	Rust-inhibitive primer, adhesion primer, seam and fastener details, reinforcement, and multiple passes.
Asphaltic roofing	Bleed-through, soft asphalt, loose granules, blisters, moisture, incompatible repairs, and surface instability.	Bleed-blocking primer, repairs, reinforcement, and additional material over rough surfaces.
Single-ply membrane	Membrane identity, talc, chalk, plasticizer, failing seams, contaminated surfaces, and incompatible sealants.	Membrane-specific cleaner and primer, adhesion testing, seam repair, and approved detail treatment.
Concrete	Moisture, outgassing, laitance, cracks, curing compounds, contamination, and profile.	Moisture evaluation, mechanical preparation, compatible primer, crack repair, and pinhole correction.
Existing silicone	Dirt, biological growth, weathering, repairs, weak underlying layers, and loss of adhesion.	Specialized cleaning, compatible silicone repair materials, adhesion testing, and additional silicone coating.
Existing non-silicone coating	Positive identification, adhesion, chalking, contamination, moisture, and chemical compatibility.	Test preparation, approved primer or tie coat, adhesion testing, and written manufacturer acceptance.

Silicone Adheres Well to Silicone—Many Other Materials Do Not

Cured silicone has low surface energy. This contributes to water resistance but can make it difficult for other coating chemistries, sealants, adhesives, tapes, and repair materials to bond to it.

Once a roof has been coated with silicone, future repairs and recoating normally require compatible silicone materials or a specifically approved preparation and tie-coat procedure.

Silicone overspray can also create adhesion problems on nearby surfaces that were never intended to receive silicone. Protect walls, metal, windows, equipment, vehicles, solar components, and adjacent roof areas.

Cleaning a Roof for Silicone

Silicone will not adhere reliably to dust, chalk, loose coating, oil, grease, biological growth, salts, talc, uncured sealant, or other contaminants. Pressure washing alone may not remove every contaminant.

The approved cleaning process may involve:

Dry removal of loose debris.
Removal of failed coatings, mastics, sealants, and repairs.
Detergent or manufacturer-approved cleaning solution.
Pressure washing at a controlled pressure suitable for the substrate.
Specialized cleaning of grease, oil, exhaust deposits, or biological contamination.
Thorough rinsing to remove cleaner residue.
Complete drying before primer, details, or coating.
Field adhesion testing after the cleaning procedure has been completed.

Wash water, cleaner, loosened contaminants, and coating debris must be contained and disposed of according to applicable requirements.

Asphalt Bleed and Discoloration

Asphaltic oils and chemicals can migrate into light-colored silicone and create yellow or brown staining. Discoloration may reduce appearance and reflectance even when the silicone remains physically intact.

A manufacturer-approved bleed-blocking primer may be required over smooth or granulated asphaltic roofing. The bleed blocker must be applied at the specified rate and allowed to dry completely before silicone is installed.

Primer that has not released its water or solvent can blister beneath the silicone. Surface dryness, elapsed time, temperature, humidity, thickness, and the manufacturer’s instructions must all be considered.

Details and Reinforcement

Field silicone coating should not be expected to repair open seams, backed-out fasteners, unstable cracks, deteriorated flashings, or active expansion joints. These conditions must be repaired using approved details.

A silicone roof system may use:

Silicone flashing-grade material.
Compatible sealant.
Polyester fabric, mesh, fleece, or manufacturer-specified reinforcement.
Self-adhered reinforcement tape approved for the system.
Liquid-applied reinforced flashing at curbs and penetrations.
Special treatment at metal seams, fasteners, end laps, and transitions.

Reinforcement should be embedded without wrinkles, fishmouths, dry areas, bridging, exposed edges, or trapped air. Required laps and coating coverage above and below the reinforcement must be maintained.

Wet-Film and Dry-Film Thickness

Because many silicone products are high in solids, their dry-film thickness may be relatively close to their wet-film thickness. The theoretical relationship remains:

Dry-film thickness ≈ Wet-film thickness × Volume-solids fraction

For example, a silicone containing 90 percent solids by volume and applied at 30 wet mils would theoretically produce:

30 wet mils × 0.90 = 27 dry mils

The calculation is theoretical. Surface texture, irregularities, pinholes, overspray, roller loss, equipment residue, waste, and application variation affect installed thickness and material consumption.

Measure wet-film thickness during application and reconcile the measured roof area with the actual quantity of material used.

One Heavy Coat or Multiple Coats?

The correct number of coats is a system requirement—not a contractor preference. A manufacturer may permit a one-coat field application for a particular system while requiring separate primer, detail treatment, and additional passes over specific locations.

Multiple coats may be required to:

Build the required total thickness.
Reduce holidays and pinholes.
Control sagging on vertical surfaces.
Accommodate rough or irregular substrates.
Provide contrasting colors for inspection.
Meet a specified warranty or tested assembly.

Do not exceed the manufacturer’s maximum thickness per coat. Excessive build can produce sagging, bubbles, surface skinning, uneven cure, or solvent entrapment.

Mixing and Container Control

Single-component does not mean no mixing or material control. Silicone pigment and fillers can settle during storage.

Verify product, color, batch, shelf life, and storage history.
Inspect containers for damage, leakage, skinning, contamination, or moisture entry.
Mix for the stated time using the specified mixer and speed.
Avoid whipping excessive air into the coating.
Do not add solvent or thinner unless the current product data expressly allows it.
Keep containers closed when not in use.
Do not return contaminated or partially cured material to the original container.

Moisture-cured material may begin reacting after the container is opened. Observe the manufacturer’s requirements for resealing and later use.

Airless Spray Application

High-solids silicone may require a high-output professional airless pump, properly sized hose, suitable gun, and large-orifice reversible tip. The coating manufacturer’s current equipment recommendation must control.

Equipment selection must consider:

Material viscosity and temperature.
Required flow rate and operating pressure.
Tip-orifice size and spray-fan width.
Hose diameter and total hose length.
Filter removal or selection.
Pressure rating of the pump, hose, fittings, gun, extension, and accessories.
Use of an approved 48-inch extension pole and properly oriented tip guard.
Manufacturer-approved flushing and cleaning solvent.

Do Not Let Silicone Cure in the Equipment

Cured silicone can be extremely difficult to remove from pumps, hoses, guns, filters, and tips. Plan material transfer, shutdown, flushing, and cleanup before spraying begins. Never assume that water will clean solvent-based or moisture-cured silicone equipment.

Spray Control and Overspray

The applicator should maintain a consistent distance and keep the spray fan as nearly perpendicular to the roof as practical. Arcing the pole gun or allowing the tip to tilt produces uneven film thickness.

Windborne silicone overspray can contaminate vehicles, windows, metal, walls, mechanical equipment, solar equipment, and nearby property. Because many materials do not adhere readily to cured silicone, contamination can create long-term problems beyond appearance.

Monitor wind speed and direction continuously.
Protect air intakes and sensitive equipment.
Use windscreens or containment where approved and effective.
Control access below and around the work area.
Stop spraying when overspray cannot be contained.
Document existing contamination and nearby property before work begins.

Silicone Can Be Extremely Slippery

Cured silicone—especially when wet, dusty, or covered with biological growth—can create a serious slip hazard. Uncured silicone can be even more hazardous.

Plan worker movement before coating begins. Provide safe access, fall protection, designated walk paths, staged work areas, and manufacturer- approved walk pads or granulated traffic surfaces where required.

Do not broadcast aggregate into a silicone system unless the complete material and procedure are approved by the manufacturer.

Dirt Pickup, Biological Growth, and Reflectance

Silicone surfaces can attract and retain dirt. Dirt pickup does not necessarily mean the membrane has failed, but it can reduce appearance and solar reflectance. Low areas may also collect sediment and support biological growth.

Reflective-roof evaluation should consider:

The exact product and color.
Initial solar reflectance and thermal emittance.
Three-year aged values.
Whether testing was performed over a smooth or rough substrate.
Expected dirt exposure and roof drainage.
The manufacturer’s cleaning and maintenance procedure.

A CRRC rating describes radiative performance. It is not an approval of waterproofing, adhesion, wind resistance, fire performance, or suitability for a particular roof.

Repairing and Recoating Silicone

Silicone can be renewed, but the existing surface must first be evaluated. The contractor should determine whether the existing silicone remains soundly adhered and whether failures are limited to the surface or extend into lower roof layers.

A repair or renewal program may require:

Removal of dirt, chalk, biological growth, grease, and contamination.
Removal of loose or poorly adhered silicone.
Repair of wet insulation, damaged substrate, seams, penetrations, and flashings.
Replacement of incompatible previous repairs.
Field adhesion tests using the proposed preparation and new silicone.
Compatible silicone flashing material and field coating.
Manufacturer-approved tie coat when coating with another chemistry is specifically permitted.

Do not apply acrylic, polyurethane, asphaltic material, tape, or generic sealant over silicone without written system approval and successful field testing.

Common Silicone-Coating Defects

Observed Condition	Possible Causes	Required Investigation
Peeling or delamination	Contamination, wrong primer, poor cleaning, wet substrate, weak existing coating, or missed recoat window.	Identify the failure plane and test adhesion around the affected area.
Blistering	Trapped roof moisture, wet primer, outgassing, solvent entrapment, or excessive thickness.	Open selected blisters and investigate moisture and layer condition.
Pinholes	Porous or textured substrate, foam cells, air entrainment, insufficient material, or poor application technique.	Determine the pinhole depth and repair before accepting the membrane.
Sags or runs	Excessive thickness, vertical application, wrong tip, low viscosity, or poor spray control.	Measure thickness and review mixing, material temperature, and application technique.
Slow or incomplete cure	Low humidity, cold temperature, excessive thickness, expired material, contamination, or incorrect product handling.	Protect the area and obtain manufacturer evaluation before recoating.
Brown or yellow staining	Asphalt bleed, contaminated water, exhaust, grease, dirt, or insufficient bleed blocking.	Identify the source before cleaning or recoating.
Splitting at details	Excessive movement, missing reinforcement, poor termination, thin coating, or substrate failure.	Evaluate the movement and reconstruct the detail using the approved method.
Excessive dirt pickup	Local environment, standing water, uncured film, soft surface, or maintenance conditions.	Evaluate cure, drainage, exposure, cleaning procedure, and coating condition.

Manufacturer Examples

Current manufacturer literature illustrates why silicone must be specified as a complete system:

GAF describes its High Solids Silicone Roof Coating as a moisture-cure silicone used within approved systems over multiple substrates, with protection against leaks associated with ponding water and a CRRC-rated white finish.
Neogard describes 7870 as a single-component, moisture-cured, high-solids silicone roof coating for approved built-up roofing, modified bitumen, concrete, metal, polyurethane foam, and single-ply roof surfaces.
Sika describes Sikalastic-500 as a single-component, high-solids, moisture-cured silicone with substrate-specific primers for metal, asphaltic roofing, concrete, polyurethane, acrylic, PVC, TPO, EPDM, and Hypalon.

These examples are educational and are not endorsements. The named product’s current data sheet, system specification, details, approvals, and warranty requirements control its use.

Silicone Roof-Coating Installation Checklist

Identify the complete existing roof assembly and every existing coating and repair material.
Determine whether the roof is structurally sound and suitable for a silicone system.
Complete a moisture investigation and remove wet or deteriorated materials.
Correct drainage, seams, flashings, penetrations, fasteners, and substrate defects.
Review the current system specification, product data sheets, safety data sheets, and detail drawings.
Verify code, fire, wind-uplift, reflectance, and warranty requirements.
Complete cleaning trials, primer trials, and representative adhesion tests.
Install the exact substrate-specific primers and bleed blockers required.
Complete and inspect all repairs, reinforcement, and flashing details.
Verify product, color, batch, shelf life, storage, mixing, and application equipment.
Measure and record environmental conditions before and during application.
Apply each coat at the specified wet-film thickness and coverage rate.
Reconcile material usage with the measured completed roof area.
Inspect for holidays, pinholes, thin areas, sags, bubbles, contamination, and incomplete cure.
Provide safe walk paths, final documentation, maintenance instructions, and the required warranty records.

Technical References and Industry Resources

Manufacturer examples are provided for education and do not constitute an endorsement. Standards, formulations, approvals, product data, and warranty requirements can change. Verify the current edition and current manufacturer documents before specifying or applying any material.

Article 17 Takeaway

Silicone roof coatings provide strong ultraviolet stability and can offer important resistance to prolonged water exposure. Their low surface energy, dirt pickup, slipperiness, specialized cleanup, and repair compatibility must also be understood.

Silicone does not correct wet insulation, an unsound roof, defective drainage, poor preparation, weak details, or insufficient film thickness.

A successful silicone roof is a specified system—not a heavy coat of white material applied over whatever happens to be on the roof.

No part of this material may be reproduced, distributed, transmitted, stored, displayed, published, or used in any form or by any means without the prior written permission of Azimuth Spray Systems, LLC, except for brief quotations used in reviews, educational discussion, or scholarly reference with proper attribution.

This material is provided for general educational purposes and is not a substitute for project-specific engineering, architectural design, manufacturer instructions, workplace-safety requirements, building codes, or professional judgment. Always consult current technical data sheets, safety data sheets, specifications, tested assemblies, approvals, and warranty requirements before beginning work.

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Tags: silicone roof coating, high-solids silicone roofing, ASTM D6694, ponding water roof coating, silicone membrane, commercial roof restoration, silicone application

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