01The three products
| Sealer | Looks | Typical life | Installed cost per sq ft |
|---|---|---|---|
| Asphalt emulsion | Opaque black film that hides the surface | 2 to 3 years | $0.15–$0.30 |
| Acrylic | Clear or tinted; the surface shows through | 1 to 3 years | $0.15–$0.30 |
| Coal tar | Black; applied in heavier coats | see below | $0.15–$0.30, often the high end |
Prices and lifespans are from asphalt emulsion vs acrylic sealer and coal tar sealer cost. The short version from the first: emulsion is paint, acrylic is varnish.
02What USGS found about coal-tar sealcoat
The US Geological Survey says most sealcoat products are either coal-tar or asphalt-emulsion based, and that coal tar and coal-tar pitch have extremely high concentrations of PAHs (polycyclic aromatic hydrocarbons) and are classified as known human carcinogens. Worn sealcoat particles are carried by rain, wind, tyres and shoes into nearby soil, streams and homes.
- In a USGS estimate, a pre-schooler living next to coal-tar-sealed pavement takes in about 2.5 times more PAHs from house dust than from diet, and nearly 10 times more with higher hand-to-mouth activity.
- Runoff collected up to 42 days after application killed all of two standard laboratory test organisms.
- After Austin, Texas, banned coal-tar sealcoat in 2006, sediment cores from Lady Bird Lake showed PAHs falling sharply.
03Where coal tar is not allowed
USGS notes that coal tar is more common east of the Continental Divide, except where states, counties or cities prohibit it. Washington is one example: under RCW 70A.440.020, coal tar pavement products labelled as containing coal tar may not be sold after January 1, 2012, and may not be applied to a driveway or parking area after July 1, 2013. Check your own state and city before you buy.
04Questions for the contractor
05Doing it yourself
Materials run about $0.05 to $0.12 per square foot against $0.15 to $0.30 installed. Most DIY failures come from three shortcuts: sealing a dirty surface, sealing over cracks instead of filling them, and one thick coat instead of two thin ones (DIY driveway sealing).
Sources used on this page
- USGS: Coal-Tar-Based Pavement Sealcoat, PAHs, and Environmental Health — PAH content, house dust, runoff toxicity, Austin ban
- Washington State Legislature: RCW 70A.440.020 — coal tar sale and application ban