As pavement maintenance contractors prepare for the sealcoating season, many who have relied on refined coal tar sealer face growing uncertainty about supply and pricing. Producers report significant price increases, and availability of coal tar sealer remains a concern. In response, manufacturers have expanded their offerings of asphalt bitumen tar emulsion-based sealers as the primary alternative. Other options, including asphalt/coal tar blends and products containing ceramics, are also available. This article examines the key differences between emulsion-based sealers and coal tar sealers, drawing on insights from industry manufacturers to help contractors make informed decisions.
Chemical Composition and Manufacturing Differences
The fundamental distinction between emulsion-based and coal tar sealers lies in their chemical makeup and how they are manufactured. These differences affect everything from performance consistency to application requirements.
Coal Tar Sealers: Standardized Specifications
All 100% coal tar sealers are produced to meet federal specifications, specifically ASTM D-5727 (which replaced RP-355e). This means that regardless of the manufacturer, pure coal tar sealers share consistent chemical and physical properties. Contractors can rely on predictable performance from batch to batch and from one producer to another. For projects that require compliance with ASTM D-5727 or Federal Aviation Administration specs P-625, P-627, or P-628, contractors must use a 100% coal tar sealer.
Asphalt Emulsion Sealers: Greater Variability
Asphalt emulsion sealers are fundamentally different. The base material used to manufacture these sealers is not produced specifically for pavement sealing applications. It may be produced for road construction or other purposes and is not made to any sealer-specific specification. This creates several challenges:
- Properties of asphalt can vary widely depending on the crude oil source. Canadian crude oil produces asphalt with different characteristics than Venezuelan crude oil.
- Refineries use different blending processes to achieve desired properties, resulting in varying chemical compositions.
- No industry-wide specifications exist for asphalt-based or blended sealer products.
- Asphalt emulsion sealers can vary substantially from producer to producer and even from batch to batch.
According to Tim Vance, president of Vance Brothers, this variability means contractors face more difficulty achieving consistent results with asphalt-based sealers. It requires more quality control by the manufacturer than coal tar sealer production does.
Blended Products: Combining Both Worlds
Many manufacturers produce blended products that combine asphalt emulsion with coal tar. The behavior of these blends depends heavily on which component dominates the formula. An 80/20 blend (80% coal tar, 20% asphalt) behaves much like pure coal tar sealer, while a blend heavy in asphalt will act more like an asphalt emulsion sealers what contractors need to know. Manufacturers caution that blends tend to cure more slowly and remain softer longer than pure coal tar sealer, because asphalt particles and coal tar particles do not fully coalesce together.
Application Requirements and Performance Characteristics
The application process differs significantly between emulsion-based and coal tar sealers. Contractors switching from one material to the other must adjust their methods to achieve optimal results.
Temperature Sensitivity and Thermoplasticity
Asphalt emulsion sealers exhibit higher thermoplasticity than coal tar sealers. Girish Dubey, president of STAR Inc., explains that thermoplasticity is the temperature at which a material becomes fluid. Asphalt-based sealer requires higher temperatures for particles to come together and form a continuous film. This means:
- Asphalt-based sealers cannot be applied unless the ambient temperature is at least 50°F (10°C).
- If applied below this threshold, film formation is jeopardized and the coating will wear out prematurely.
- Coal tar sealers are more forgiving at lower temperatures, giving contractors greater application flexibility, particularly in spring and fall.
Moisture and Humidity Sensitivity
Asphalt emulsion sealer is significantly more susceptible to moisture and high humidity than coal tar sealer. Chris Mariani, vice president of marketing for GemSeal, warns that contractors who push the limits with asphalt-based sealers as they might with coal tar can encounter consequences not experienced before. Coal tar contractors often develop a comfort level with the material’s expected performance and may extend its limits, but asphalt-based sealers are more fragile and require strict adherence to weather limitations.
Dilution Ratios and Aggregate Requirements
Asphalt emulsion sealers cannot be diluted more than 25% with water, whereas coal tar sealers tolerate a wider range of dilution. Over-diluting an asphalt emulsion sealer will compromise performance. Joe Conwell, vice president of sales for Neyra Industries, notes that contractors switching from coal tar need to follow dilution recommendations much more closely with asphalt emulsion sealers.
Sand aggregate requirements also differ. Neyra’s 2007 asphalt emulsion sealer formulation, for example, increased from 3 pounds of silica sand per gallon to 5 pounds per gallon. The additional aggregate improves performance in three ways:
- Faster drying time
- Improved skid resistance
- Extended coating lifespan
Drying Time and Curing Considerations
Drying time and curing behavior represent some of the most practical differences between these two sealer types. These factors directly affect project scheduling, labor costs, and customer satisfaction.
Dry Time Between Coats
Asphalt emulsion sealers dry slower than coal tar sealers. Under ideal weather conditions, contractors should allow at least 8 hours between coats. However, 24 hours is preferable, particularly during spring and fall when temperatures are lower and humidity is higher. This extended drying time has significant business implications:
- Contractors must factor the additional time into their bids.
- A 24-hour drying requirement often means a second trip to the jobsite, something coal tar contractors are not accustomed to.
- Customers used to one-stop contractor visits or nighttime sealcoating may need to adjust their expectations.
Film Formation and Curing Comparison
| Property | Coal Tar Sealer | Asphalt Emulsion Sealer | Blended Product |
|---|---|---|---|
| Specification compliance | ASTM D-5727 | No standard spec | No standard spec |
| Minimum application temperature | Below 50°F possible | 50°F or higher | Depends on dominant component |
| Maximum water dilution | More forgiving | 25% maximum | Varies by formula |
| Drying time between coats | Standard | 8-24 hours | Slower than either pure type |
| Moisture sensitivity | Low | High | Moderate |
| Film cure time | Faster | Slower | Slowest |
| Consistency across batches | High | Variable | Variable |
| Long-term durability | Superior | Good with polymer modification | Intermediate |
Blended products present additional curing challenges. Bill Maclean of The Brewer Co. explains that film formation takes longer with blends because individual particles of tar and asphalt do not coalesce together. The cured coating remains softer and more tender than what contractors are used to with coal tar sealer. This softer film is more vulnerable to traffic damage during the extended curing period.
Choosing the Right Sealer: Practical Guidance for Contractors
Selecting between emulsion-based and coal tar sealers requires careful evaluation of project requirements, weather conditions, and customer expectations. The industry experts interviewed for this article offer several practical recommendations.
Matching Sealer Type to Project Specifications
Before selecting a sealer, contractors must review bid requirements carefully. If the project specification calls for material meeting ASTM D-5727, or FAA specs P-625, P-627, or P-628, then a 100% coal tar sealer is mandatory. No asphalt-based or blended product can meet these specifications. For projects without such requirements, contractors have more flexibility and can choose based on cost, availability, and performance expectations.
Transitioning Between Sealer Types
For contractors switching between coal tar and asphalt emulsion sealers during the season, proper tank cleaning is critical. Conwell recommends that before adding an asphalt-based sealer to a tank that contained coal tar, the tank should contain no more than 10% residual coal tar. For a 500-gallon tank, this means draining it down to 50 gallons or less before adding the new material. Getting as much of the previous product out of the system as possible prevents compatibility problems.
Industry producers also emphasize the importance of clear communication between contractor and supplier. Contractors should ask specific questions when trying a new product:
- How does this product need to be handled differently than coal tar sealer?
- What is the maximum dilution ratio?
- Does the product contain polymer modifiers?
- Is the sealer compatible with the additives I currently use?
- Is it compatible with the previous product residue in my equipment?
The Role of Polymer Modification
Many manufacturers now offer polymer-modified asphalt emulsion sealers that significantly improve performance. GemSeal’s asphalt-based sealer, for example, contains polymers to maximize the performance of the binder used in making the coating. These polymer-modified products are more expensive than non-modified asphalt sealers but deliver enhanced durability. However, even with polymer technology, manufacturers acknowledge that today’s asphalt-based sealers cannot match coal tar mile for mile in long-term performance, though that may change in the future as formulation technology continues to advance.
Market Trends and Contractor Adoption
Neyra Industries reported that a significant number of customers switched from coal tar to asphalt emulsion sealer in the previous season, and early indications showed that many of those who switched continued using the asphalt-based product. This suggests that with proper education and adjusted application methods, contractors can achieve satisfactory results with asphalt emulsion sealers.
Contractors should also consult resources on asphalt safety comprehensive guide to hazard management in and asphalt plants and pavement construction equipment a complete for additional guidance on safe handling and equipment best practices.
Key Takeaways for Decision-Making
- Coal tar sealers offer superior durability, consistency, and faster curing, but face supply constraints and price increases.
- Asphalt emulsion sealers are more widely available and improving in quality but require stricter application controls and longer drying times.
- Blended products offer a compromise but cure slower than either pure material and may not meet specification requirements.
- Polymer-modified asphalt sealers provide better performance but at a higher cost.
- Contractors must readjust their application methods when switching between sealer types, particularly regarding dilution, aggregate content, and weather limitations.
- Open communication with the sealer supplier is essential to understand both the capabilities and limitations of each product.
The sealcoating market is evolving. While coal tar remains the benchmark for performance, the growing availability and improving quality of asphalt emulsion sealers give contractors viable alternatives. The key to success lies in understanding the distinct characteristics of each material and adjusting application practices accordingly. By staying informed about product differences and maintaining close communication with manufacturers, contractors can select the right sealer for each project and deliver results that meet customer expectations.