ASTM D6947
Liquid-Applied Polyurethane Coating for Spray Polyurethane Foam Roofing
Last updated: March 28, 2026
Overview
ASTM D6947/D6947M is the standard specification for liquid-applied moisture-cured polyurethane coatings used in spray polyurethane foam (SPF) roofing systems. The current revision is D6947/D6947M-07, reapproved in 2021. It is maintained under ASTM Committee D08 on Roofing and Waterproofing.
While the standard was written for SPF roofing, polyurethane coatings are also used on other roofing substrates where high physical performance is needed. Manufacturers, architects, and spec writers reference D6947 when specifying polyurethane roof coatings for projects that demand superior abrasion and impact resistance.
Polyurethane coatings offer the best abrasion and impact resistance of the three major coating types (acrylic, silicone, polyurethane), making them the go-to choice for roofs with foot traffic, mechanical equipment, or other sources of physical wear. For a broader look at how roof coatings work, see our guide on elastomeric roof coatings.
Quick reference: D6947 covers polyurethane coatings only. For acrylic roof coatings, see ASTM D6083. For silicone roof coatings, see ASTM D6694. Each chemistry has its own standard with different test requirements.
Key Requirements
D6947 defines minimum performance thresholds for polyurethane roof coatings. The tensile strength requirement alone (1500 psi) is roughly 7 to 10 times higher than what acrylic and silicone standards require, reflecting the tougher chemistry.
| Property | Requirement | Test Method |
|---|---|---|
| Tensile Strength | 1500 psi minimum | ASTM D412 |
| Elongation | 75% minimum | ASTM D412 |
| Tear Resistance | 50 lbf/in minimum | ASTM D624 |
| Abrasion Resistance | Per standard (Taber abraser) | ASTM D4060 |
| Impact Resistance | Per standard | ASTM D2794 |
| Accelerated Weathering | 1000 hours minimum | ASTM G154 |
| Water Vapor Permeance | 3 perms maximum | ASTM E96 |
| Volume Solids | 65% minimum | D6947 procedure |
What These Numbers Mean in Practice
The 1500 psi tensile strength is what sets polyurethane apart. Acrylic coatings (D6083) require just 200 psi. That difference translates directly to resistance against foot traffic, dropped tools, and abrasion from rooftop equipment.
The elongation requirement (75%) is lower than acrylic (100%) because polyurethane is a harder, more rigid film. It stretches less but resists physical damage far better. The tear resistance test (ASTM D624) and abrasion test (ASTM D4060, Taber abraser) specifically measure how the coating holds up under mechanical stress.
The very low permeance limit (3 perms max, compared to 12 perms for acrylic) means polyurethane creates a nearly vapor-tight barrier. This is important for SPF systems where the foam insulation must stay dry to maintain its R-value.
Watch out: The 1000-hour weathering requirement is half what D6083 requires for acrylics (2000 hours). Polyurethane coatings are more susceptible to UV degradation and often require a topcoat or aliphatic formulation for long-term UV stability. Check the manufacturer's TDS for UV resistance details.
When to Use Polyurethane
Polyurethane roof coatings cost more than acrylic or silicone, but they earn that premium in specific situations where physical durability matters most.
Best Applications
- High-traffic roofs where maintenance crews walk regularly
- Areas around rooftop HVAC equipment and mechanical units
- Walkway pads and designated access paths
- Parking decks and vehicular traffic areas
- SPF roofing systems (the original intended use of D6947)
- Any roof where impact from dropped tools or equipment is a concern
When to Choose Something Else
Polyurethane is not the right choice for every roof. If your primary concern is ponding water, silicone coatings (ASTM D6694) are a better fit because they do not soften or blister with prolonged water exposure. Polyurethane can degrade when water sits on it for extended periods.
For standard commercial re-coating jobs with minimal foot traffic, acrylic coatings ( ASTM D6083) are typically more cost-effective and provide adequate performance.
Tip: Many contractors use a hybrid approach on larger roofs. Polyurethane goes on walkways, equipment pads, and high-traffic zones. A less expensive acrylic or silicone coating covers the rest of the field. This balances durability where you need it with cost savings on the larger area.
Frequently Asked Questions
Why is polyurethane more expensive than acrylic or silicone?
The chemistry costs more to produce, and the performance reflects that. Polyurethane delivers 1500 psi tensile strength compared to 150 to 200 psi for silicone and acrylic coatings. You also get significantly better abrasion and impact resistance. The higher price is justified on roofs where physical wear is the primary failure mode.
Can I use polyurethane where water ponds?
Not recommended. Polyurethane coatings can soften and blister with prolonged water exposure. If your roof has areas where water sits for more than 48 hours after rain, use a silicone coating (ASTM D6694) in those areas instead. Silicone is chemically inert to water and will not degrade from ponding.
Is polyurethane roof coating the same as spray foam?
No. Spray polyurethane foam (SPF) is the insulation substrate that gets applied to the roof deck. The polyurethane coating covered by D6947 is the protective topcoat applied over the foam. They use related chemistry but serve completely different purposes. The foam provides insulation and structure, while the coating provides weather protection and UV resistance.
