You're standing in the concrete aisle holding a tube of crack filler, and the crack in your driveway has been bothering you since spring. You've watched the videos and it doesn't seem that bad. What's stopping you is that you don't want it to look unsightly and you certainly don't want to make it worse, and you've read enough reviews from people whose filler didn't even last a year before every crack came back.
The honest answer is yes, for the right crack, and it's one of the few concrete jobs we'll tell you to do yourself. The catch is that the tube that's easiest to grab is often the wrong one, and a Denver winter is very good at finding out.
The short version, if you're standing in the aisle
Can I just fill the cracks in my concrete driveway myself with a tube from the hardware store?
Yes, if the crack is narrow, both sides sit level, and it hasn't grown. Use a flexible polyurethane sealant rather than a rigid cement patch, because the crack opens and closes with the temperature and a rigid filler crumbles the first winter. If one side sits higher than the other or the crack keeps widening, something under the slab is moving, and no tube will fix that.
Which cracks are a tube job and which aren't
Most cracks in a driveway or patio are just concrete being concrete. It shrinks as it cures and it moves a little with the seasons, and a thin crack with both sides level is cosmetic. The reason to fill it is water, more than looks. Denver runs around a hundred freeze-thaw cycles a year, and water that gets down into a crack and freezes will widen it a little each time. Keeping water out during the winter is the whole job.
So a crack up to about the width of a pencil, flat on both sides and no longer than it was last year, is a fair DIY job. Fill it and keep an eye on it.
The ones to leave alone are different in a way you can check in a minute. Run your shoe across it. If one side catches your toe, the slab has moved, and a lot of the metro sits on clay that swells wet and shrinks dry, so it will keep moving. A crack that's noticeably wider than last fall is telling you the same thing. So is a crack with soil washing out of it or a hollow sound when you tap beside it. You can fill those, but it's premature, because the cause is still there and the filler will tear by spring. That's a concrete repair question, and it starts with finding out what moved.
Why the filler in the reviews didn't last a year
When a DIY repair doesn't last through one winter, it usually comes down to one of four things.
Usually it's the wrong product. The small squeeze bottles and the trowel-on cement patches cure hard. A crack in a slab opens in the cold and closes in the heat, every day in a Front Range winter, and a rigid filler can't follow it. It cracks again along the edges, then water gets behind the patch, freezes, and pops it out. What holds up is a flexible polyurethane sealant made for concrete, the kind that comes in a caulk-gun tube and stays rubbery after it cures.
Next is a dirty or damp crack. Sealant sticks to clean, dry concrete and to nothing else. If there's dust, old filler, weeds or moisture in there, it bonds to that instead and peels out in a strip.
Depth catches people out as well. Squeezing sealant into a deep crack until it's full wastes the tube and makes a worse repair, because a thick plug can't stretch. Foam backer rod, which is a cheap grey rope sold in the same aisle, gets pushed into the crack first so the sealant sits as a shallow band on top of it.
Then there's the calendar. Most of these products want the concrete dry and above forty or fifty degrees while they cure, and the label on the tube will give you the exact number. Put it down too late in the year and it never cures properly before the temperature drops.
How to do it so it holds
Pick a dry stretch with mild afternoons, which in Denver means early October is about the end of the comfortable window. Clean the crack out with a screwdriver or a wire brush, then blow or vacuum the dust out of it. If you rinse it, give it a full day or two to dry.
Push backer rod into anything deeper than about half an inch, leaving it a little below the surface. Run the sealant in slowly and keep it just under flush, since a bead standing proud of the surface is the first thing a tire or a snow shovel catches. Stay off it for as long as the label says.
Be ready for how it looks. Grey sealant doesn't match grey concrete, and people are often surprised by how much the line shows. A light dusting of dry sand over the bead while it's still wet takes the shine off and helps it blend, but a filled crack still looks like a filled crack. If the look matters more than the water, that's worth knowing before you start.
Plan on redoing it, too. UV at this altitude breaks sealants down faster than the packaging suggests, so check the bead each fall and expect to cut out and replace sections every few years.
When it's worth having someone look instead
A few cracks filled well will get a sound slab through a lot of winters. Where the tube stops making sense is when there are cracks everywhere, when panels have shifted, or when the surface around the cracks is flaking as well. Sealant doesn't fix a base that has failed, and at some point you're spending weekends on a slab that needs a panel or two replaced. That's often a smaller job than people expect, because damage tends to stop at a control joint, and it's the same approach we describe for a driveway that's only failing at the street end.
If the cracks are fine and it's the worn look of the whole slab that bothers you, resurfacing covers the surface, though only once the cracks underneath have stopped moving. An overlay over a live crack will crack in the same place.
And if you're doing this now because you're worried about what winter will do, the cracks are only part of it. The rest of the pre-freeze list, the drainage and the sealing, is in why concrete looks fine in October and terrible in April.
If you're not sure which kind of crack you have
Lay a coin beside the crack for scale, take one photo straight down and one from a few steps back, and call us at (720) 782-8086. If it's a tube job we'll tell you so and tell you which tube. If the slab has moved, we'll come out, find out why, and give you a written price for repairing it properly before you spend a weekend on something that won't hold.