Common Asphalt Sealcoat Mistakes

Most sealcoat failures are visible before the first coat goes on: dirt and oil still on the surface, cracks left open, a cold forecast, or a plan for one thick coat instead of two thin ones. Check those four items first, because each one is cheap to fix now and expensive to fix after the coating peels or tracks.

What mistakes ruin an asphalt sealcoat job?

The mistakes that ruin a job fall into three groups: the surface was not ready, the weather was wrong, or the coating went on too thick, too thin, or too soon. A product that fits the pavement still fails when any of those three groups is wrong, and a second coat over a bad first coat does not repair the first mistake.

Sealing new asphalt too soon

Fresh asphalt carries light oils that must leave the surface before sealcoat can bond. SealMaster states this two ways on its own documents, which is why no single wait time should be quoted as a universal rule. Its sealcoating FAQ gives a minimum of 30 to 60 days and requires the surface to be free from oils. Its Coal Tar Concentrate sheet gives a minimum of four weeks under ideal weather at 70 degrees Fahrenheit. Trade practice summarized by PavemanPro goes further: the Pavement Coatings Technology Center practice calls for a minimum of 90 days above 70 degrees Fahrenheit, checked with a water-break-free test in which clean water sheets out without oil rings.

Use the label of the product you bought as the controlling figure, and use the oil check as the physical test. If the surface still shows oil, or the label cure time has not passed, waiting costs nothing. Sealing too soon traps oils under the film, and the film then scuffs and peels instead of protecting the pavement.

Skipping cleaning and oil-spot priming

Sealcoat bonds to clean asphalt, not to dirt, loose material, or oil. SealMaster specifies cleaning immediately before sealing, by power blower or mechanical sweeping, and its FAQ adds the repair step: fill cracks with crack filler and treat gas, oil, and grease spots with a primer such as PetroSeal or PrepSeal. The STAR FAQ states the failure plainly: peeling comes from sealer not bonding to oil spots or other surface contaminants.

Clean until the surface is bare asphalt, then prime each oil spot and let the primer do its work before coating. A spot that is only swept over, or only covered with a thicker pass of sealer, stays a weak bond under the film and peels first.

Sealing over open cracks or a failed base

Sealcoat is a surface film. It does not fill a wide crack, level a failed base, or fix drainage, and a thicker pass does not change that. Fill cracks with crack filling material before coating, as the SealMaster FAQ directs. For alligator cracking, the pattern of small connected cracks that looks like alligator skin, PavemanPro warns that the surface needs examination for base failure, with tan or white streaks along the cracks as a sign that the base itself has failed.

When the base has failed, the repair decision comes first and the sealcoat decision comes after it. Coating a failed base hides the damage for one season and leaves the same failed base under a fresh black film.

Buying a product the local rule bans

Coal tar sealcoat carries a high polycyclic aromatic hydrocarbon load, and that fact drives local bans. The U.S. Geological Survey states that coal-tar-based products are typically 20 to 35 percent coal tar or coal-tar pitch, and Minnesota Statutes section 116.202 prohibits the sale and use of coal tar sealant products, effective 1 January 2014. The full product comparison, including fuel resistance and solids, sits in the companion product guide.

Check the rule at the exact address of the pavement before buying, because a product that is legal in one city can be banned in the next. This check belongs before purchase, not after the buckets are on site.

One thick coat instead of two thin coats

SealMaster recommends a minimum of two coats, with a third coat on high-traffic areas on high-traffic areas. Two thin coats cure better than one thick coat because sealers cure by water release: a thin coat releases water fast, while a thick coat holds water, stays soft for longer, and tracks, as the STAR FAQ explains.

The fixture from the companion product guide shows what the per-coat amount means. For a drive that nets 940.5 square feet, or 104.5 square yards, the SealMaster Coal Tar Concentrate mixed rate of 0.11 to 0.13 gallon per square yard per coat gives:

1. One coat: 104.5 x 0.11 = 11.495 gallons and 104.5 x 0.13 = 13.585 gallons, shown as 11.5 to 13.6 gallons.
2. Two coats: 11.495 x 2 = 22.99 gallons and 13.585 x 2 = 27.17 gallons, shown as 23.0 to 27.2 gallons.

Result: one pass that carries 23.0 to 27.2 gallons in a single layer is not two coats. It is one coat at twice the per-coat amount, and it cures like a thick coat. Apply 11.5 to 13.6 gallons, let that coat dry, then apply the second coat. The rate belongs to that named product sheet. Another product sheet states a different rate, and its own rate replaces these figures.

Adding water beyond the mixing directions

SealMaster specifies mixing in accordance with the manufacturer specification for the sealer being used, and diluting only if the mix design allows it. Water beyond that point lowers the solids of the mix as applied, which means less protective material stays on the pavement after the water leaves. The companion product guide shows the same effect in numbers: SealMaster states 55 to 57 percent applied solids for its polymer-modified coal tar sealer, against 40 to 43 percent for conventional sealers.

Mix exactly as the sheet states, including sand and additive where the mix design calls for them. Extra water makes the mix easier to spread and harder to defend, because the film left behind is thinner than the sheet promises.

Coating in cold weather or before rain

SealMaster sets the weather rule in one sentence: temperature must be a minimum of 50 degrees Fahrenheit and rising for a period of not less than 24 hours, with no application when rain is forecast within 24 hours. The Coal Tar Concentrate sheet repeats the 50 degree minimum for the 24 hours after application. A coat that goes on at 50 degrees in the morning and faces a cold night below that limit, or rain before it cures, does not get a second chance to cure correctly.

Check the forecast for the full 24 hours after application, not just the hour of coating. If the forecast fails either test, the job waits. A delayed job costs a day. A washed or cold-cured coat costs a recoat.

Opening to traffic too soon

SealMaster requires the final coat to cure a minimum of 24 hours before opening to traffic, and the same 24-hour cure applies before traffic marking paint goes on. Tire traffic before that point tracks uncured sealer onto uncoated pavement and into buildings, and the tracked areas then need recoating while the rest of the film is already cured.

Plan the closure for the full cure time, including the second coat, before the first coat goes on. A driveway that must carry a car at 6 a.m. needs its final coat finished a full day earlier, not late the night before.

Recoating a sound film too often

Sealcoat is a thin film, and repeated coats over a sound film build up a thick layer that can crack and peel instead of adding protection. Recoat when the film has worn thin, the aggregate shows through, and the surface again needs protection, not on a calendar date alone. The product guide gives the reapplication range for coal tar products, and the label of the product in use controls the interval for that product.

When the film is still sound, the useful work is crack filling and cleaning, not another coat. Save the recoat for the season the film actually needs it.

Pre-coat checklist

• Label cure time for new asphalt passed, and the surface is free from oils.
• Surface cleaned to bare asphalt, cracks filled, and every oil spot primed.
• Failed base areas repaired instead of coated.
• Local rule checked at the pavement address, and the product family fits fuel exposure.
• Per-coat amount calculated from the label rate, with two coats planned.
• Mix prepared exactly as the sheet states, with no extra water.
• Forecast holds 50 degrees Fahrenheit and rising, with no rain within 24 hours.
• Full 24-hour traffic closure planned after the final coat.