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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Polyurethane Roof
Coating & Urethane
Roofing Systems

Urethane roof coatings, spray polyurethane foam roofing and polyurea explained: how each works, where each wins, and how to choose for your building.
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  • Roof type and age
  • Approximate square footage
  • Leaks, ponding or rust
  • Interest in added insulation
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2 systems
Coating or spray foam roof: know which
Industry usage
2.5–3 lb
Per cubic foot, roofing-grade spray foam
SPFA
R-6+
Approx. R-value per inch, closed-cell foam
Manufacturer data
Base + top
Aromatic base coat, aliphatic topcoat
Product data sheets

Polyurethane is one of the most versatile materials in roofing, which is why “polyurethane roof” confuses people. It can mean a liquid-applied urethane roof coating rolled or sprayed over an existing roof, or a spray polyurethane foam (SPF) roof that adds insulation and is then protected by a coating. Both are proven commercial roofing systems. We manufacture polyurethane and polyurea coatings and spray foam, so here is a straight comparison.

Quick answer

A polyurethane roof coating is a liquid-applied urethane membrane, usually an aromatic base coat plus an aliphatic topcoat, that cures into a tough, flexible film over metal, single-ply, built-up or foam roofs. It is known for high tensile strength, foot-traffic and impact resistance. Spray polyurethane foam roofing adds a seamless layer of closed-cell insulation, then gets a protective coating. Polyurea is a faster-curing cousin that builds thicker in one visit.

What's in this guide
  1. 1Two kinds of polyurethane roofs
  2. 2Coatings compared
  3. 3Spray foam roofing
  4. 4Which fits
  5. 5Installation
  6. 6FAQ
Start here

Two kinds of polyurethane roofs

Coating

Liquid urethane roof coating

A base coat and topcoat, typically 20–40 mils total, applied over an existing roof to waterproof and protect it. Moisture-cured and often solvent-borne.

Foam

Spray polyurethane foam roof

Closed-cell foam sprayed 1 inch or more thick to insulate and slope the roof, then sealed with an elastomeric coating. See spray foam roofing.

Polyurea

Fast-cure alternative

Spray polyurea cures in seconds and builds thicker per visit. See polyurea roof coating.

Compare

Urethane vs polyurea vs silicone vs acrylic

PropertyUrethane coatingPolyureaSiliconeAcrylic
Toughness and trafficVery goodExcellentFairFair
Typical system thickness20–40 mils40–80+ mils20–30 mils20–30 mils
CureHours, moisture cureSecondsHoursWeather dependent
Ponding waterGoodGoodVery goodPoor
UVAliphatic topcoat neededAliphatic topcoat neededExcellentGood
Odor and VOCSolvent-borne grades have odorEssentially noneLow to moderateLow
EquipmentRoller or airlessPlural-component rigAirlessAirless
Typical values; product data sheets govern. Compare all coating types in our roof coating guide.
Insulate too

Spray polyurethane foam roofing

An SPF roof is sprayed directly onto the deck or existing roof, adheres fully and can be built thicker at low spots to improve drainage. It adds continuous insulation with no seams or fasteners. The foam is then protected with an elastomeric coating, often silicone, acrylic, urethane or polyurea, and sometimes granules for extra UV and impact protection. See spray foam roof granules.

Field noteThe coating over foam is a maintenance item. Inspect it regularly and recoat before the foam is exposed; UV-damaged foam has to be removed before recoating.
Choose

Which polyurethane roof fits your building?

Urethane coating

Sound roof, needs waterproofing

Good for metal and single-ply roofs that are dry and sound but leaking at seams and fasteners.

SPF roof

Needs insulation and drainage

Adds R-value and fixes ponding with tapered foam over the existing roof.

Polyurea

Traffic, impact, fast turnaround

Thick seamless membrane sprayed in a day.

Replace first

Wet or failed roof

Saturated insulation or rotten decking must be fixed before any coating system.

Do it right

Installation basics

  1. Moisture survey

    Find and replace wet insulation.

  2. Clean and repair

    Pressure wash, fix seams, treat rust, secure flashings.

  3. Prime

    Use the primer the coating maker specifies for the substrate.

  4. Base coat

    Apply the aromatic base coat, reinforcing seams and details.

  5. Topcoat

    Apply the aliphatic or reflective topcoat to the specified thickness.

  6. Inspect

    Check thickness and adhesion and document for the warranty.

Polyurethane roofing

Insulate, waterproof, protect.

A certified ArmorThane applicator can survey your roof and quote a urethane, spray foam or polyurea roof system.

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FAQ

Polyurethane roof questions

What is a polyurethane roof coating?

A liquid-applied urethane membrane, usually an aromatic base coat and an aliphatic topcoat, that cures into a tough, flexible, waterproof film over an existing roof.

How long does a polyurethane roof last?

Urethane coating systems commonly last 10 to 20 years depending on thickness and maintenance. Spray foam roofs can last decades when the protective coating is maintained and periodically recoated.

Is urethane or silicone better for a roof?

Urethane is tougher and better for foot traffic and impact. Silicone has better UV and ponding resistance and is easier to apply, but is softer and only silicone sticks to it later.

What is the difference between polyurethane and polyurea roof coatings?

Both come from isocyanate chemistry. Urethane coatings cure over hours; polyurea reacts in seconds, builds thicker per visit and needs plural-component equipment.

Can you put polyurethane foam over an existing roof?

Often yes, if the existing roof is dry and sound. Wet insulation and damaged decking must be removed first.

AT
Written by the ArmorThane technical team. We have manufactured polyurea, polyurethane and polyaspartic coatings, spray foam and plural-component spray equipment in Springfield, Missouri since 1989. Roof system selection should follow the building owner requirements, local code and the manufacturer specification.

Sources

  1. Spray Polyurethane Foam Alliance, SPF roofing resources. sprayfoam.org
  2. ASTM D6947, liquid-applied moisture-cured polyurethane coating for SPF roofing. astm.org
  3. Cool Roof Rating Council, roof product ratings. coolroofs.org

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Tough roofs start with urethane chemistry.

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