How to Fill the Gap Between Your Garage and Asphalt Driveway

Use something flexible. The joint between a concrete garage slab and an asphalt driveway moves with temperature, frost, and settling, so rigid fillers like mortar or concrete crack out quickly. For a narrow gap, up to about 1/2 inch, a pourable or caulk-style asphalt crack filler or a self-leveling joint sealant works well. For a gap between about 1/2 inch and 1 1/2 inches, press in foam backer rod first and put sealant on top. If the gap is wider than that, or the driveway has dropped below the garage floor, you're past sealing. That calls for a patch or a partial repave.

Asphalt crack filler guide → Sunken driveway repair →

Why the Gap Forms

A few things usually cause the separation:

• Settling. Soil next to a foundation often gets dug out and backfilled when the house is built. If it wasn't compacted well, it settles over the years, and the driveway sinks and pulls away from the slab.
• Different materials. Concrete and asphalt expand, contract, and move differently. The joint between them takes that stress.
• Frost. In cold climates, water that gets into the joint freezes and pushes things apart.
• Edge wear. The last few inches of asphalt next to the slab can crumble, especially if the driveway was thin there or the base was soft.

Related: What the Joint Between Paver Passes Should Look Like

Why You Should Fill It

It's not just about looks. An open gap lets water run down alongside and under the garage slab and the driveway. Over time that can soften the base under the asphalt, speed up settling, feed frost heave in winter, and invite weeds and ants. Sealing the joint keeps water out and slows all of that down.

Size Up the Gap

Gap	Height difference	Best fix
Up to about 1/2 inch	Level or nearly level	Asphalt crack filler or self-leveling joint sealant
About 1/2 to 1 1/2 inches	Level or nearly level	Foam backer rod plus sealant
Wider than about 1 1/2 inches	Any	Patch with asphalt, or cut and repair the edge
Any width	Driveway sits lower than the garage floor	Build up with patch or repave the strip; sealant won't fix a drop

Related: How Much Concrete for a 12x20 Garage Slab?

What You'll Need

• Stiff brush, putty knife, or screwdriver to clean the joint
• Shop vac or leaf blower
• Closed-cell foam backer rod, sized slightly larger than the gap
• Asphalt crack filler, or a self-leveling polyurethane joint sealant made for horizontal joints
• Caulk gun if using tubes
• Gloves

Step-by-Step: Sealing a Narrow to Medium Gap

1. Clean it out. Pull weeds, scrape out dirt and crumbled asphalt, and vacuum or blow the joint clean. The sealant needs clean, sound edges to stick to.
2. Let it dry. The joint should be completely dry. Give it a sunny day after rain.
3. Install backer rod (for gaps wider than about 1/2 inch). Push the foam rod into the gap so it sits below the surface, leaving room for sealant on top. A blunt tool like a paint stirrer helps. The rod keeps you from wasting sealant filling a deep void, and it helps the sealant stretch properly.
4. Apply the sealant or filler. Run a steady bead along the joint. Self-leveling products will flow flat. Stop slightly below the top of the slab.
5. Keep it a little low. A sealant line that sits a hair below the surface won't get caught by snow shovels, plow blades, or tires.
6. Let it cure. Keep traffic off it for the time listed on the product. Some polyurethanes need a day or more.

When the Driveway Has Dropped

If the asphalt has sunk so there's a lip at the garage door, sealant alone won't solve it. Water will still collect at the low edge, and tires will keep hammering it. Options:

• Small drop (up to about an inch): Build up the low edge with cold patch, compacted in thin layers, tapering it out a couple of feet into the driveway. Seal the joint once cured.
• Larger drop or crumbling edge: A paving contractor can cut out a strip of asphalt along the garage, fix and compact the base, and repave it level with the slab. This is a common and relatively small job.
• Ongoing settling: Look for a water source, like a downspout dumping next to the garage, and fix it first.

Tips for a Longer-Lasting Joint

• Redirect downspouts so they don't empty onto the joint.
• Keep the driveway sloped away from the garage so water runs out, not in.
• Check the joint every fall. Touch up any cracks before winter.
• Seal the joint before sealcoating the rest of the driveway.

Materials and Cost Checklist

Before you start, measure the gap in three or four spots along the door. Gaps are rarely even, so buy for the widest section.

• Backer rod: pick a diameter about 25% wider than the gap so it stays put by friction. A 3/4-inch gap usually takes 1-inch rod.
• Sealant coverage: a 10-oz tube covers far less than people expect on a wide joint. Check the coverage chart on the tube (it is listed by joint width and depth) and multiply by the width of the door opening.
• Primer: some polyurethane sealants call for a primer on concrete. Read the label before you start, not after.
• Painter's tape: run it along the garage slab edge if you want a clean line on the concrete.

How to Tell if the Fix Is Working

1. After the first hard rain, look for water standing at the door or wicking under the slab edge.
2. Each fall, press on the sealant with a thumb. It should feel rubbery and stick to both sides. If it has pulled away from one side (adhesion failure), cut that section out and redo it.
3. After winter, check for new spalling at the asphalt edge. Crumbling there usually means the edge needs patching, not more sealant.

Bottom Line: Choosing a Driveway-to-Garage Gap Filler

Keep the joint between your garage and driveway sealed with something flexible. Clean it well, use backer rod for wider gaps, keep the sealant slightly low, and check it every fall. If the driveway has sunk or the gap is very wide, patch or repave the strip instead of trying to caulk your way out of it.