ASTM D6694
Liquid-Applied Silicone Coating Used in Spray Polyurethane Foam Roofing Systems
Last updated: March 28, 2026
Overview
ASTM D6694/D6694M is the standard specification for liquid-applied silicone coatings used in spray polyurethane foam (SPF) roofing systems and other roofing substrates. It defines the minimum performance requirements that a silicone roof coating must meet to be considered compliant. The current revision is D6694/D6694M-15 (reapproved 2021), maintained under ASTM Committee D08 on Roofing and Waterproofing.
Silicone roof coatings are moisture-cure, single-component systems. Unlike acrylic coatings, silicone does not re-emulsify in water, which makes it the go-to choice for roofs with ponding water or poor drainage. Manufacturers, architects, and contractors reference D6694 when specifying silicone coatings for commercial and industrial roofing projects.
Quick reference: D6694 covers silicone coatings only. For acrylic roof coatings, see ASTM D6083. For polyurethane roof coatings, see ASTM D6947. Each chemistry has its own standard with different test requirements.
Key Requirements
D6694 defines minimum performance thresholds across several test categories. A product must pass all of these to claim conformance.
| Property | Requirement | Test Method |
|---|---|---|
| Tensile Strength | 150 psi minimum | ASTM D412 |
| Elongation | 100% minimum | ASTM D412 |
| Tear Resistance | 20 lbf/in minimum | ASTM D624 |
| Water Immersion (7 days) | No blistering, cracking | ASTM D471 |
| Accelerated Weathering | 1,000 hours, max 10% elongation loss | ASTM G154 or G155 |
| Water Vapor Permeance | 15 perms maximum | ASTM E96 |
| Volume Solids | 90% minimum | D6694 procedure |
| Dirt Pickup Resistance | Tested per D6694 procedure | D6694 procedure |
What These Numbers Mean in Practice
The 150 psi tensile and 100% elongation requirements ensure the coating can handle thermal expansion and contraction without cracking. Silicone coatings tend to be softer and more flexible than acrylics, which is why the tear resistance test (ASTM D624) is included here but not in the acrylic standard.
The water immersion test is critical for silicone coatings. The coating is submerged for seven days and inspected for blistering, cracking, or delamination. This is the test that validates silicone's core advantage: it can sit in ponding water without breaking down.
The 90% volume solids minimum is much higher than acrylic coatings (50%). This means silicone coatings shrink very little during cure. What you put on wet is close to what you get dry, so coverage calculations are more straightforward.
Watch out: D6694 sets minimum thresholds. Premium silicone coatings often exceed these significantly. For example, a high-end product might have 300 psi tensile and 250% elongation. Check the Technical Data Sheet for actual tested values, not just "meets D6694."
Silicone vs Acrylic
Silicone (D6694) and acrylic (D6083) are the two most common roof coating chemistries. They solve different problems and each has clear trade-offs.
| Factor | Silicone (D6694) | Acrylic (D6083) |
|---|---|---|
| Ponding Water | Handles it well | Will re-emulsify and fail |
| Volume Solids | 90%+ (minimal shrinkage) | 50%+ (significant shrinkage) |
| Recoating | Silicone over silicone only | Can be recoated with most chemistries |
| Dirt Pickup | Tends to attract more dirt | Better dirt resistance |
| Cost | Higher material cost | Lower material cost |
| Weathering Test | 1,000 hours | 2,000 hours |
The biggest practical difference is ponding water. If a roof has areas where water sits for 48 hours or more after rain, silicone is the right choice. Acrylic coatings are water-based and will soften and eventually fail when submerged for extended periods.
The recoating limitation is the main downside of silicone. Once cured, silicone has a very low surface energy, which means almost nothing adheres to it except more silicone. If you decide to switch to acrylic or polyurethane later, you will need to remove the silicone coating first. For more on coating types, see our elastomeric roof coating overview.
Tip: For the ASTM D6083 acrylic standard details, including its full requirements table and practical guidance, see our dedicated D6083 page.
Frequently Asked Questions
When is silicone better than acrylic?
Silicone is the better choice for low-slope roofs with ponding water or poor drainage. If water sits on any part of your roof for more than 48 hours after rain, acrylic coatings will eventually swell, blister, and fail in those areas. Silicone will not re-emulsify in standing water, so it holds up where acrylic cannot.
Can I apply acrylic over silicone?
No. Nothing adheres to cured silicone except more silicone. This is the most common recoat failure in the field. Cured silicone has an extremely low surface energy, so acrylic, polyurethane, and other coatings will peel off. If you need to switch away from silicone, the existing coating must be removed first.
Why is the volume solids requirement so high?
Silicone coatings are 90%+ solids compared to about 50% for acrylic. The rest of the coating is solvent or water that evaporates during cure. Higher solids means less shrinkage, so the wet film thickness is much closer to the final dry thickness. This makes coverage calculations more predictable and reduces the number of coats needed to hit the specified dry mil thickness.
