Seal Coat Specifications — Asphalt Emulsion, Application Rate, and Sand Additive
Material and application specifications that separate a properly executed commercial seal coat from a coating that peels or fades within one season.
Sealant Material Specification
We use refined petroleum asphalt emulsion sealant meeting ASTM D2939 Standard Specification for Emulsified Bitumens Used as Protective Coatings. The formulation contains refined petroleum asphalt as the binder, water as the carrier, and polymer modifiers for improved abrasion resistance. We do not use coal-tar sealant—coal-tar products contain polycyclic aromatic hydrocarbons (PAHs) that are classified carcinogens by the National Toxicology Program and are banned or restricted by several municipalities and states. Asphalt emulsion provides comparable or better durability in Utah conditions, is significantly lower in VOC emissions during application, and is the correct specification for properties with storm water discharge into sensitive watersheds. Minimum content specification: 30 percent asphalt solids content by weight, polymer-modified for improved flexibility and abrasion resistance.
Application Rate and Coat Count
Standard commercial specification: two coats of asphalt emulsion at a combined application rate of 0.20 to 0.30 gallons per square yard (0.022 to 0.033 gallons per square foot). Each coat is applied at 0.10 to 0.15 gallons per square yard. The first coat penetrates the oxidized asphalt surface, sealing micro-cracks and restoring binder oils. The second coat, applied after the first coat achieves tack-free state (typically 2 to 4 hours at 70°F), builds film thickness and provides the abrasion-resistant wear surface. A single thin coat achieves inadequate film build and fails to protect high-traffic areas—single-coat applications are appropriate only for new asphalt refreshes where penetration is the primary goal and traffic volume is low. We do not offer single-coat application on primary commercial lots as a standard service.
Sand Additive Specification
We add silica sand to the sealer at a rate of 3 to 5 pounds per gallon of concentrated sealer. The sand additive serves two purposes: (1) it provides slip resistance on the cured surface—smooth seal coat on a commercial lot creates a skating-rink surface when wet; (2) it adds bulk to the film, improving wear resistance in high-traffic areas. Sand gradation: clean, dry silica sand graded to ASTM C33 fine aggregate specification, or a purpose-manufactured pavement sealant sand with 70 to 100 mesh gradation. Too-fine sand (<100 mesh) adds little traction; too-coarse sand (>30 mesh) creates a rough texture that accelerates tire wear on the coating. We adjust sand loading rate for drive aisles (higher rate for better traction) versus parking stalls (standard rate).
Cure Requirements and Minimum Application Conditions
Minimum ambient temperature at time of application: 50°F, rising. Minimum pavement surface temperature: 55°F. Maximum humidity: 90 percent relative humidity. Rain-free window required: 24 hours after application for vehicle traffic; 4 hours for foot traffic. Wind: moderate wind (under 20 mph) accelerates surface drying; high wind (over 20 mph) disrupts spray-applied emulsion and causes overspray onto vehicles or adjacent surfaces. Temperature must remain above 50°F for the first 24 hours of cure—if a cold front is forecast to push temperatures below 50°F within 24 hours of application, we will not proceed. Application during periods of direct sunlight on a hot surface (pavement surface over 120°F) causes premature surface skinning before the emulsion fully penetrates—we schedule applications for morning starts on hot summer days.
Recent Seal Coat Maintenance Projects
Common Questions
- What is the difference between asphalt emulsion and asphalt-based filler sealers?
- Pure asphalt emulsion sealer contains refined petroleum asphalt as its primary binder—it has genuine penetrating and adhesive properties that bond to the pavement surface. "Asphalt-based filler" products contain less asphalt and more filler materials (clay, silica powder, water). Filler sealers cost less but have lower solids content, thinner film build, and shorter service life. We use only petroleum asphalt emulsion with a minimum 30 percent asphalt solids content.
- Can seal coat be applied over seal coat that is still in good condition?
- Yes. Asphalt emulsion bonds well to a previously sealed surface that is in sound condition—not peeling, not contaminated with oil, and not excessively worn through to bare asphalt. Re-sealing over a sound existing coat adds film build and refreshes the surface. However, avoid over-building film thickness through excessive applications: more than 4 to 5 cumulative coat layers over 10 years can cause the coating to crack as a unit rather than flex with the underlying pavement.
- Is there a specification sheet or SDS for the sealer you use?
- Yes. We provide the sealant product SDS (Safety Data Sheet) and technical data sheet on request. These documents are relevant for properties with NPDES storm water permit requirements or for clients who want to verify VOC compliance with municipal regulations.
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