Hot rubber crack filling, before winter finds the crack

Why this matters more than the coating

If you could only do one thing to a driveway or a lot before an Ohio winter, it would be this, not sealcoating. That is an unusual thing for a sealcoating company to say and it happens to be true.

Sealer is a surface coating. It protects sound asphalt from sun, salt, and surface water, and it is genuinely worth doing. But an open crack is not a surface problem. It is a direct channel from the sky into the base underneath the pavement, and the base is the part you cannot repair cheaply.

Water gets down that channel, saturates the aggregate base, and freezes. Frozen water occupies about nine percent more volume than liquid water, so it pushes outward in every direction, lifting and separating the pavement around it. Then it thaws, leaving a slightly larger void and a slightly wider crack, and the next rain fills it again. Toledo goes through that cycle dozens of times a winter. That is how a hairline crack becomes a half-inch gap in three years, and how a half-inch gap becomes a pothole in five.

Hot rubber versus the bottle from the hardware store

The cold-pour crack filler sold in a jug at a big box store is not the same product, and the difference is not marketing.

Cold pour is a liquid emulsion that cures by evaporating water out of itself. Because it loses volume as it dries, it shrinks back down into the crack, and by the second freeze it has usually pulled away from at least one wall of the crack, which reopens the channel it was supposed to close. It also stays relatively rigid, so pavement movement splits it.

Hot-applied rubberized filler is a solid at room temperature. It gets melted in a kettle to around 350 degrees, goes into the crack as a liquid, and returns to solid as it cools without losing volume. Just as importantly, it stays flexible in cold weather, which matters because a crack is not a static thing. Pavement contracts in winter and expands in summer, so the crack is widest in January, exactly when a rigid filler is most likely to fail.

How the work is done

Cracks get cleaned out first. A crack full of dirt, gravel, and dead grass gives the filler nothing to bond to, and filler that bonds to debris rather than pavement pops out the first winter. That means compressed air, wire wheel where a crack has vegetation growing out of it, and killing that vegetation rather than covering it.

The filler goes in hot and slightly overfilled so that it settles flush rather than dished. On a driveway the finished line is squeegeed flat so it does not sit proud and catch a snow shovel.

Then, if the surface is also being sealed, the sealer goes over the top. The filled cracks will still be faintly visible as darker lines under the coating on close inspection, and any company promising you an invisible repair is promising something the material cannot do.

What cannot be crack filled

• Alligator cracking, the interconnected pattern that looks like reptile skin, is not a crack problem. It means the base under that section has failed and the pavement is flexing. Filling it seals a symptom while the cause keeps spreading. Those areas get cut out and patched instead.
• Very fine hairline surface checking, thinner than roughly an eighth of an inch, will not accept filler and does not need it. That is what the sealcoat is for.
• Cracks wider than about an inch, or with the edges crumbling away, usually need routing or partial patching first so there is a sound wall for the filler to bond to.

The best time of year to do it

Late summer and early autumn, which is right now. There are two reasons, and they pull in the same direction.

First, the obvious one: this work is specifically defence against freeze-thaw, so it wants to be finished before the first hard freeze. In Northwest Ohio that means having it done by roughly mid-October.

Second, the less obvious one: cracks are at their narrowest in the heat of summer, because the pavement has expanded. Filling in early spring, when a crack is at its widest, means the filler gets squeezed as the pavement expands into summer. Late summer through early autumn is the sweet spot where the crack is close to its middle width and there is still curing weather.

Questions people ask about crack filling