Crack Down the Middle of Your Asphalt Driveway: Seam Cracks Explained

A long, straight crack running lengthwise down the center of your driveway is most often a paving seam. Most driveways are wider than a paving machine lays in one pass, so the crew paves one strip, then a second strip beside it. Where the two meet is a joint, and joints are the weakest line in the pavement. As the asphalt ages, shrinks in cold weather, and flexes under tires, that joint tends to open into a crack. It's usually not a sign of structural failure. It is, however, a direct path for water into the base, so it's worth cleaning and sealing before it widens. If the crack wanders, has a dip beside it, or branches into a web, something else is going on.

Asphalt crack filler guide → New driveway cracking →

Why Seams Form in the First Place

A paving machine lays a strip only as wide as its screed, and the smaller pavers common on residential jobs can't cover a wide two-car driveway in one go. So the crew makes two or more passes side by side. Crews do their best to lay the second pass while the first is still warm so the two knit together, and they overlap and pinch the joint with the roller. Even so, the joint usually ends up slightly less dense than the rest of the mat.

Over time, three things work on that joint:

• Temperature swings. Asphalt contracts in cold weather, pulling the weakest line apart.
• Oxidation. The binder hardens and loses flexibility with sun exposure.
• Water. Once a hairline opening forms, water gets in and freeze-thaw cycles widen it.

Is It a Seam or Something Worse?

Walk the length of the crack and look closely.

What you see	Likely cause	Level of concern
Straight, centered, even width	Paving joint	Low, seal it
Straight, but along an old utility trench	Trench settlement	Moderate, may need a patch
Crack with a dip or sag beside it	Base moving	Higher, investigate
Cracks branching into a web pattern	Base failure	High, repair the area
Near the edge, running parallel	Weak edge support	Moderate

A seam crack typically stays straight and uniform. If one side is lower than the other, or the area feels soft underfoot, the base may be settling. Our guide on cracks in a new asphalt driveway covers early cracking in more detail.

How to Fix an Asphalt Driveway Crack Down the Middle

Hairline to About 1/4 Inch

1. Clean it out. Yank any weeds, dig loose debris from the gap with a screwdriver, then blast it clear with a leaf blower or compressed air.
2. Let it dry. Crack filler won't bond to a wet crack.
3. Fill it. Use a flexible, rubberized crack filler rated for asphalt. Pourable and squeeze-bottle products work well for narrow seams.
4. Smooth it. A squeegee or putty knife levels the filler with the surface.
5. Let it cure per the label before driving on it or sealcoating over it.

The walkthrough on choosing and applying crack filler goes deeper on product types.

Wider Than About 1/4 Inch

Wider cracks need more material and often a foam backer rod pushed into the crack first so the filler doesn't sink out of sight. The guide to using backer rod shows how.

Cracks That Open and Close

Some seam cracks noticeably widen in winter and narrow in summer. These "working" cracks do best with professional hot-pour sealant, often after the crack is routed into a clean channel so the sealant has more to grip. A 2006 field manual from the Texas Pavement Preservation Center at the University of Texas at Austin, produced under a Texas DOT research project, recommends routing for cracks that move about a tenth of an inch or more over a year. Many sealcoating and paving contractors offer this service.

A Note on Timing

Late summer and early fall are good times to deal with a seam crack. The pavement is warm and dry, crack fillers cure well, and you close the gap before winter water can get in and freeze. Cold-pour fillers generally need mild, dry weather to set, so check the temperature range printed on the container before you start.

Crews can reduce future seam trouble by warming the cold edge before placing the next pass, a technique explained in can you reheat asphalt.

Should You Seal Over It?

Sealcoat alone won't close a crack. Fill the seam first, let it cure, then sealcoat the driveway if it's due. Sealcoat over an open crack just leaves a dark line that keeps letting water in.

Preventing Seam Cracks on a New Driveway

If you're getting a driveway paved, ask the contractor:

• How many passes will it take, and where will the joint fall?
• Will you pave the second pass while the first is still hot?
• How will you compact and seal the joint?

Placing the seam out of the main wheel paths can help. Good compaction at the joint is the best defense.

If your driveway is brand new, check the seams during the new driveway walkthrough before the crew leaves.

Bottom Line on a Crack Down the Middle of the Driveway

A straight asphalt driveway crack down the middle is usually a paving joint that has started to open. Keep water out by cleaning, drying, and filling it with a flexible asphalt crack filler, using backer rod for wide gaps and hot-pour for cracks that move with the seasons. If you spot a dip, soft ground, or branching cracks, look beyond the seam at the base.