In cold climates, water seeps in and destroys the asphalt when it expands during freezing. If you plan to topcoat your driveway, you'll need to fix the cracks first.
You can buy squeeze bottle and caulk tube–style crack filler products from any home center. They're quick and easy to apply, but they shrink and crack and don't last very long. However, there's another way to fill asphalt cracks: with melt-in filler that doesn't shrink—the same type used by highway crews. The melt-in material and trowelable cover mix cost about $100 for a typical driveway.
It'll take almost a full day to repair several cracks if they're 20 ft. long or so, but the repairs will last much longer than other quick fixes. In addition to the melt-in and trowel mix products, you'll need a propane torch with an extension hose, and a leaf blower or compressed air gun. Use an angle grinder fitted with a diamond wheel to widen hairline cracks and to quickly remove previously applied crack fillers.
We used melt-in 1/2-in.-diameter Latex-ite Pli-Stix Crack and Joint Filler and Latex-ite Trowel Patch for this project. Our driveway had several 25-ft.- long cracks. So we bought four 30-ft. packages of the crack filler and four 2-gallon pails of the trowel patch. We already had a propane torch. But we bought a 5-foot extension hose to eliminate the flame-outs that occur when you tip a propane cylinder upside down (WH0159 Bernzomatic Universal Torch Extension Hose).
Choose a sunny day with no rain in the forecast for at least 24 hours. Start by rolling the crack filler rope onto a sunny section of the driveway so it warms and softens. While it's warming, remove all the dirt, weeds and old crack filler from the cracks. Scrape out the old material with a flat-blade screwdriver or 5-in-1 paint tool. It's a painstaking process, but it's critical to getting a successful repair. So don't skip it or take shortcuts. Cleaning and filling hairline cracks are more time consuming, and the fix won't last unless you widen them with an angle grinder and diamond wheel (Photo 1).
Once you finish digging out all the cracks, blow the dust and debris out of the cracks and off the driveway using a leaf blower or compressed air gun.
Push the melt-in filler deep into the cracks (Photo 2). If any filler bulges above the surface of the driveway, cut off the excess with a knife or compress it so it sits below the surface (Photo 3). Then screw the extension hose onto your propane tank and mount the torch to the other end and fire it up. The melt-in filler burns easily, so don't try to melt it in one fell swoop. Using just the tip of the flame, slowly melt the filler (Photo 4). If the filler starts to burn, blow out the flames and use a faster sweeping motion or move the flame farther from the crack.
Allow the filler to cool to the touch (at least 20 minutes) before covering it with the trowel patch material. Then lay down a bead of trowel patch and smooth it (Photo 5). Let the trowel patch dry overnight. Apply a second coat if you see a depression where the crack was filled.
Asphalt driveways can develop pitted areas from motor oil and coolant contamination and repeated freeze/thaw cycles. If the pits are 1/2 in. or less, you can fill them with a spreadable filler product. (We used Latex-ite Trowel Patch again.)
Clean oil stains and prime with oil stain primer. Then coat the entire pitted area with patch material and let dry overnight (Photo 1). Apply a second coat to top off any partially filled pits (Photo 2) and smooth the surface. Let dry.