Asphalt fails from the top down. Sun oxidizes the binder, water works into the surface, and the lot goes grey and brittle before it starts breaking up.
Sealcoating puts a barrier over prepared asphalt to slow that down. It is not a repair, a working crack has to be filled first, or it comes straight back through the sealer within a season. We fill, then seal, then re-stripe once it has cured.
Asphalt is stone held together by bitumen, and the bitumen is the part that ages. Ultraviolet and oxygen break the binder down at the surface, fines wash out, the exposed stone starts to loosen, and a black lot goes grey and then brittle. Sealcoating puts a sacrificial layer over the top to slow that down. It does nothing for the structure underneath.
The sequence, start to finish
Preparation takes longer than the application. It also matters more. The lot gets blown and swept, or washed where the grime has bonded to the surface, edges and curb lines cut back where dirt and vegetation have crept in, and the surface checked for whatever will ruin a coat. Standing water. Loose or raveled areas. Oil.
Oil and fuel spots want treating separately. Petroleum dissolves the bitumen it lands on, so asphalt under a long-standing drip is already softened, and sealer straight over the top lifts within weeks and leaves a bare ring. Those get cleaned, then treated with an oil spot primer so the sealer has something to hold.
Cracks are filled before anything else goes down. Sealer is a thin coating and cannot bridge a joint that is still moving, so sealing over an unfilled crack hides it until the first temperature swing opens it back through the new surface. Low spots that hold water may want mastic or a patch. A puddle sitting on fresh sealer for two days thins it and wears it off first.
Application is squeegee, broom or spray, and most jobs use some combination. Squeegee and broom work material into the surface texture and give the better bond, which is why they get used for a first coat and on rough or porous asphalt. Spray covers ground faster and looks more even, so it suits a second coat over a surface already sealed. Edges, curb lines and anything around an obstruction get cut in by hand whatever is happening on the open lot.
Materials, and how a mix goes wrong
Common sealer types are refined tar emulsion, asphalt emulsion, and petroleum-based polymer modified products. Availability differs by jurisdiction, some local authorities restrict coal tar based products, so the right answer for a given lot depends on what is permitted where you are, the condition of the surface, and how much fuel spillage it sees.
Whatever the base product, sealer ships as a concentrate and gets mixed on site with water, sand and sometimes an additive. The manufacturer publishes exactly how much of each. That mix design is where most sealcoating jobs are won or lost, and it is invisible once the material is on the ground.
Over-dilution with water is the classic corner cut. It spreads further, covers more square footage per drum, looks black and glossy for a couple of weeks, then wears back to grey inside a season. Sand is what gives the surface texture and wear resistance, so a coat mixed short of sand is slick when wet and thin under traffic. Neither of those shows up on the day you write the check.
More coats are not automatically better. Sealer applied repeatedly without wearing down builds a thick brittle film that eventually cracks in a fine web across the whole surface, and that has to come off rather than be covered. Two coats on a properly prepared lot at the correct spread rate is the normal specification.
| Corner cut | How it looks on the day | What it costs you later |
|---|---|---|
| Over-diluted with water | Spreads further, black and glossy for a couple of weeks | Wears back to grey inside a season |
| Mixed short of sand | Indistinguishable at handover | Slick when wet, thin under traffic |
| Extra coats sold as a bonus | Looks generous | A thick brittle film that cracks in a fine web and has to come off, not be covered |
Weather, cure and the calendar
Sealer cures by losing water to the air. It wants surface and air temperature above the manufacturer minimum and rising, and a dry window well past the point where the surface looks dry. A shower a few hours after application can wash an uncured coat into the storm drain.
Charlotte summers give plenty of warm days and interrupt them reliably. Storms build fast in the afternoon and half the time are nowhere in the morning forecast, so sealcoating here tends to be a morning trade with a hard stop, and crews watch radar rather than the printed forecast. Humidity stretches cure time even on a hot day. At the other end of the year, cool nights and heavy dew limit how late in the season a coat can go down safely, however warm the afternoon felt.
Newly paved asphalt has to release its surface oils before it will take sealer at all. That waiting period is set by the sealer manufacturer and the paving contractor and it is measured in months, not days. Sealing new asphalt early does not protect it, it just produces a coat that never bonds.
Staging on a working property
A sealed section is out of use longer than a striped one. Traffic cannot go back on until the coat has cured, and striping cannot go on until after that, so the honest sequence for a full lot is fill, seal, cure, stripe. Usually across more than one visit, and worth saying out loud at quote stage rather than discovering on the day.
Most sites get done in halves or quarters with barricades rather than cones, because a car driven across curing sealer leaves marks that do not come out and the driver takes the material home on their tires. Where a property genuinely cannot give up a section during trading hours the work moves to a weekend. Somewhere with a lot of turning traffic in one spot, a drive-through lane or a delivery apron, will show power steering scuffs in the first few weeks even on a good coat. That settles as the surface hardens.
Signs the job was done badly
- Grey patches inside the first season. Usually over-dilution, or a spread rate below specification
- Bare rings where the oil spots were, so the spots were never primed
- Cracks back through the new coat within months. Sealed over instead of filled
- A slick surface when wet, which points to a mix short of sand
- Tracking onto entrance mats and into the building. Lot reopened too early
- Fine web cracking across the whole surface, a coat built up too thick over too many applications
What to insist a quote states
- The product name, so somebody can pull the technical data sheet
- The mix design. Water, sand and additive per unit of concentrate
- Number of coats and the intended spread rate
- Application method for the open lot, and separately for the edges
- Crack filling and oil spot priming, included or excluded
- Is striping included afterwards, and how long after
- Cure time before traffic, and the sectioning plan that goes with it
Questions worth putting to a contractor
- Does this lot actually need sealing yet, or is the surface still sound?
- Which areas would you patch instead of seal, and what happens if we leave them?
- How many square feet per drum are you working to, and where does that number come from?
- What is the plan if a storm comes through two hours after you finish?
- When the lot gets re-striped afterwards, are the accessible spaces going back exactly as they were, or corrected? A car space wants 96 inches with a 60 inch access aisle, and a re-seal is the cheapest moment to fix a layout that has drifted
A contractor willing to tell you the lot can wait another year is generally the one to keep. Sealcoating on the wrong cycle is money spent early rather than money saved.