Sealcoating · Residential
Asphalt Emulsion vs Coal Tar Sealer
Most homeowners never ask what a contractor is putting on their driveway, and most contractors do not volunteer it. The two products in common use behave differently, cost differently and carry very different environmental profiles, and in a county where a large share of the land drains toward drinking water reservoirs that last point is not academic.
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Ask about asphalt emulsion vs coal tar sealer
Refined coal tar sealer is a byproduct of coking coal. It is durable and it resists petroleum well, which is why it became standard on commercial lots. It also contains polycyclic aromatic hydrocarbons at concentrations far above asphalt-based products, and PAHs are the reason a growing number of municipalities and several states have restricted its use. The concern is runoff and the dust worn off the surface over time.
Asphalt emulsion sealer is made from the same bitumen already in your driveway, suspended in water. It carries a small fraction of the PAH content, it is what we apply on every job, and on a residential driveway the performance difference is not what a salesperson will tell you it is. Coal tar's real advantage is under constant fuel and oil exposure, which describes a truck yard rather than a home.
Additives matter too. Sand or fine aggregate in the mix restores traction on a freshly sealed surface, which is worth asking about on any driveway with real slope, and there are plenty of those in Worcester, Millbury and Spencer.
What is actually in the two products
Refined coal tar sealer is a byproduct of coking coal. It is durable and resists petroleum well, which is why it became standard on commercial lots and fuel yards. It also contains polycyclic aromatic hydrocarbons at concentrations far above asphalt-based products.
Asphalt emulsion sealer is made from the same bitumen already in your driveway, suspended in water with additives. PAH content is a small fraction of coal tar's. It is what we apply on every job.
Why the difference matters in Worcester County specifically
PAHs are the reason a growing number of municipalities and several states have restricted refined coal tar sealants. The concern is runoff, and the dust worn off the surface and tracked around over the years the coating is in service.
A substantial share of the land in this county drains toward the Wachusett Reservoir, which supplies drinking water to Greater Boston. Holden, West Boylston, Rutland, Sterling and parts of Boylston sit inside that watershed, and Southborough sits within the Sudbury watershed. Choosing a lower PAH product in that context is a straightforward call, and on a residential driveway it costs you nothing in performance.
Additives, traction and slope
Freshly sealed asphalt is smoother than the weathered surface it replaced, and on a steep drive that is noticeable until it wears in. Silica sand or fine aggregate blended into the sealer restores texture and is worth asking about on any driveway with real grade.
There are plenty of those around here. The drumlin streets in Worcester, the valley sides in Millbury, and the hill lots in Spencer and Leicester all produce approaches steep enough that winter traction is a genuine consideration rather than a detail.
How Massachusetts conditions drive the specification
Massachusetts sets frost depth at 48 inches. A driveway has no footings, so nothing physically reaches four feet, but the frozen zone does, and anything frost can lift it will lift. That makes the base and its drainage the whole structural argument on residential work in this state.
Hot mix here is produced to the MassDOT Standard Specifications, Section 460, using Superpave designs graded by nominal maximum aggregate size. A residential surface course is normally a 12.5 mm mix; a binder course underneath is typically 19.0 mm. Dense graded asphalt needs a compacted lift at least three times the nominal maximum aggregate size, so 12.5 mm wants roughly an inch and a half minimum and 19.0 mm wants nearer three. A coarse mix laid too thin cannot lock its stone together and ravels from the first winter.
Compaction is where the money goes and nobody can see it
Hot mix leaves the plant around 275 to 300 degrees and stops accepting compaction near 185. Everything a roller will ever achieve has to happen inside that window, which shrinks fast on a cool day, on a thin lift, or with wind across the site. Target density on a properly rolled mat sits in the low to mid nineties as a percentage of theoretical maximum.
A few percentage points below that and the mat is permeable. Water then lives inside the asphalt rather than on top of it, and every freeze-thaw cycle works from within. This is why two driveways that look identical on the day of paving can be ten years apart in service life, and why laydown temperature and roller pattern matter more than the brochure the material came with.
Dig Safe, permits and paperwork
M.G.L. c. 82 s. 40 requires Dig Safe notification at least 72 hours before excavation so utilities can mark their lines. It is free and we file it. What it does not cover is private underground work on your own property: septic tanks and leach fields, wells, irrigation, invisible fencing, propane lines and power runs to outbuildings. Tell us where those are, because heavy equipment over a leach field is an expensive mistake Dig Safe will not catch.
Massachusetts also requires a written contract for residential work over $1,000 under M.G.L. c. 142A, and registration under that law gives you access to the state Guaranty Fund. Ask any contractor for their HIC number before paying anything.
What is included
Scope of work
- Asphalt emulsion sealer on every job
- Aggregate additive for traction where slope requires
- Full disclosure of product and manufacturer on request
- No refined coal tar products
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Common questions
Before you book
Is coal tar sealer banned in Massachusetts?
Restrictions on refined coal tar sealants vary by state and by municipality rather than being uniform nationally, so the answer depends on where you are. We do not use it regardless. Given how much of Worcester County drains toward the Wachusett Reservoir, using a lower PAH product is the straightforward call and it costs you nothing.
Does asphalt emulsion last as long?
On a residential driveway, near enough that the difference is not what decides the outcome. What decides it is surface preparation, application temperature and cure time. A well applied emulsion seal on a clean dry surface outperforms a coal tar coat rushed onto a damp one every time.
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