How to Fill Cracks in an Asphalt Driveway

Filling cracks is the cheapest way to make a driveway last longer, but only if the product fits the crack. This guide covers which cracks to fill, which to patch, which filler to use for each width, and how much to buy.

First, identify the crack

Crack filler only works on cracks in pavement that is otherwise sound. The pattern of the crack tells you whether filling will help or whether the problem is underneath.

Caltrans' crack treatment guide notes that edge cracking "cannot always be treated with crack sealants." It also says extensive crack sealing, such as sealing alligator cracking, "is not cost effective." Pavement Interactive likewise says fatigue cracks are usually too extensive for crack sealer and need a patch or reconstruction.

Crack width decides the method

Federal guidance divides crack treatment into two jobs. Crack sealing uses flexible, specialized materials in "working" cracks that open and close with temperature. Crack filling uses ordinary materials in cracks that barely move. The FHWA crack treatment manual uses about 3 mm (1/8 inch) of yearly movement as the dividing line. It recommends sealing for working cracks 5 to 19 mm wide (about 1/4 to 3/4 inch) and filling for non-working cracks 5 to 25 mm wide (about 1/4 to 1 inch).

On a driveway, cracks running across the drive are the ones most likely to move. Use a flexible, rubberized product on those.

Also look at the crack edges. FHWA treats a crack as a filling candidate only when edge damage (spalls and side cracks) covers less than about half its length. If most of the crack edge is broken up, repair the area instead of filling it.

Choosing a crack filler

The life figures come from the SHRP/FHWA field experiments on roads, not driveways. They show the relative ranking well. Rubberized and modified materials outlast plain emulsion, and preparation matters as much as the product. Pavement Interactive reports an average crack-seal life of about 3 to 8 years.

When to do it: weather and season

• Spring or fall is ideal. FHWA recommends sealing at moderately cool temperatures, about 45 to 64°F. At those temperatures the crack sits near the middle of its seasonal movement, so the filler is not overstretched in winter or squeezed into a bump in summer.
• Follow the label minimum. Cold-pour driveway products typically require 50 to 55°F and rising, with no rain expected for 24 hours. One trowel-grade data sheet also says the temperature must not drop below 50°F for 24 hours after application.
• Dry cracks only. Water in the crack stops the filler from bonding. Wait a dry day or two after rain, or dry the crack with a heat lance or torch if you are using hot-pour.

In practice, pick a dry, mild afternoon in spring or early fall, and avoid hot midsummer days when cracks are at their narrowest.

Step-by-step: filling a driveway crack

1. Clean it out

Pull weeds and grass, and scrape out dirt and loose asphalt with a screwdriver, wire brush or crack-cleaning tool. Blow the crack out with compressed air or a leaf blower. If you hose it out instead, let it dry completely. One data sheet says no standing water should be in the crack.

2. Rout (optional)

Highway crews often rout (widen) working cracks into a clean reservoir. Caltrans lists a 1/2 × 1/2 inch rout for 1/4 to 3/8 inch cracks. Routing helps hot-pour sealant last longer. Most homeowners skip it; if you do, clean very thoroughly.

3. Install backer rod in deep cracks

Backer rod is a round foam cord. It holds the filler up near the surface so you don't pour it into a crack that runs through the whole asphalt layer. Choose a rod about 25% wider than the crack, as FHWA recommends, so it stays put when pressed in. Push it down so it sits about 1/2 to 1 inch below the surface. Caltrans recommends keeping sealant no more than about 1 inch deep and setting the rod 0.5 to 1 inch below the pavement.

4. Fill

• Pourable filler: Cut the spout small and let it flow in. Stop slightly below the top and let it settle, then top off.
• Trowel-grade: Press it in and strike it flush with a trowel or squeegee.
• Hot-pour: Pour or wand it in hot. You can leave it flush or slightly overbanded (spread past the edges). Caltrans keeps the overband to no more than 2 inches wider than the crack.

Finish flush with the surface or just below. A raised hump can be caught by a snow shovel or plow, and a deep dip holds water.

5. Top off, sand and cure

Water-based fillers shrink as the water evaporates. One retail data sheet lists solids of only about 45% and warns that wide cracks may need extra applications. Top off the next day if the filler has sunk. Dust fresh filler with fine sand to stop tracking. Keep cars off it until it is firm. One label gives 4 to 8 hours to set and 24 to 48 hours for a full cure.

How much crack filler do you need?

Treat the crack as a long, thin box and convert cubic inches to gallons (1 US gallon = 231 cubic inches):

For depth, use the depth you will actually fill, down to the top of the backer rod, not the full crack depth.

Add an allowance. By the formula, a gallon would fill about 308 ft of 1/4 × 1/4 inch crack. One manufacturer rates the same size at 200 ft per gallon, so its label already assumes about 50% more material. That covers shrinkage, uneven cracks and spills. As a rule of thumb, multiply your result by 1.5 for water-based cold-pour filler. The 120 ft example then becomes about 1.3 gallons, so buy two 1-gallon jugs. For backer rod, buy the total length of the deep cracks plus about 10%.

When cracks mean the base is failing

Filling is preventive maintenance. It cannot fix structural damage. Plan a repair instead when you see:

• Alligator cracking, especially where tires run or cars park. It means the base or subgrade is giving way.
• Sinking or movement at the crack: one side lower than the other, or flexing when you drive over it. FHWA says vertical defects like these call for patching or milling, not crack treatment.
• Potholes or missing chunks. Fill them with cold patch or hot mix. Our cold patch calculator tells you how many bags to buy.
• Cracks everywhere. FHWA's guidance says many cracks, or badly deteriorated cracks, signal advanced decay. At that point sealing is "uneconomical and technically unsound," and a surface treatment or resurfacing makes more sense.

If much of the drive looks like this, compare patching with resurfacing: see our driveway lifespan guide and the driveway cost calculator.

After filling: sealcoat at the right time

Crack filling and sealcoating work best together. Fill first, let the filler cure, then seal. One crack filler label recommends waiting at least a week in good weather before applying driveway sealer. Use the sealcoat calculator to plan the sealer. If the driveway is brand-new, it is not ready for either. New asphalt has to cure first; see how long asphalt takes to cure. For timing across the year, see the best time of year for driveway work.

Frequently Asked Questions

What is the best way to fill large cracks in an asphalt driveway?

For cracks wider than about 1/2 inch, clean them, push in backer rod so the filler is no more than about 1 inch deep, then fill with trowel-grade filler or hot-pour rubberized sealant. Above about 1.5 inches, or where the edges are crumbling, patch instead.

Should I fill cracks before sealcoating?

Yes. Sealcoat is a thin coating and will not fill cracks. Fill cracks first and let the filler cure. One label asks for a week in good weather before sealer goes on. Then sealcoat over the top.

What temperature do you need to fill driveway cracks?

Most cold-pour fillers need 50 to 55°F and rising, with no rain for 24 hours. FHWA considers moderately cool spring and fall weather, about 45 to 64°F, ideal for sealing because cracks are near the middle of their seasonal movement.

How long does asphalt crack filler last?

FHWA field studies found plain emulsion fillers lasted about 2 to 4 years. Rubber-modified fillers lasted 6 to 8 years, and rubberized sealants in routed cracks lasted 5 to 9 years. Good cleaning and dry cracks make the biggest difference.

Do I need backer rod for driveway cracks?

Use it in cracks deeper than about 1/2 inch. It saves filler, stops it sinking out of sight and lets it flex. Choose a rod about 25% wider than the crack.

Can you fill alligator cracks with crack filler?

It is not worth it. Alligator cracking comes from base failure, and Caltrans calls sealing it not cost effective. Cut out the damaged area and patch it, ideally to full depth.

Is it worth filling hairline cracks?

Usually not. Most fillers cannot get into cracks under about 1/4 inch, and highway agencies typically skip them. Sealcoat covers them; fill them once they widen.

Sources

• FHWA, Materials and Procedures for Sealing and Filling Cracks in Asphalt-Surfaced Pavements: Manual of Practice (FHWA-RD-99-147): seal vs fill criteria, timing, backer rod sizing, performance.
• Caltrans, MTAG Volume I, Chapter 4: Crack Sealing, Crack Filling and Joint Sealing: crack types, width limits, routing table, backer rod depth, overband width.
• Pavement Interactive, Crack Seals: purpose, materials, typical life, fatigue cracking.
• Gardner-Gibson, Blacktop Driveway Crack Filler data sheet: 3/8 in maximum, 55°F and rising, coverage, cure and sealer wait.
• SealMaster, Trowel Grade Crack Filler technical data sheet: up to 1 in cracks, 50°F limits, coverage.