How to Fill Expansion Joints in Concrete Driveways
Expansion joints are one of the most overlooked yet critical features of a concrete driveway. They’re designed to absorb movement and prevent cracking as the concrete expands and contracts with weather changes. But when left open or neglected, these joints can become entry points for water, dirt, and even weeds, leading to premature surface damage and costly repairs.
In this guide, you’ll learn how to properly fill expansion joints using simple tools and high-performance sealants. Whether you’re working on a new driveway or maintaining an older one, following the right process ensures long-lasting protection and clean curb appeal.
What Are Expansion Joints in Concrete?
Expansion joints are narrow spaces between concrete slabs that allow the material to expand and contract with temperature changes. If left unfilled, these joints can:
- Collect water and debris
- Encourage weed growth
- Cause surface cracking over time
- Lead to freeze-thaw damage in cold climates
Why You Should Fill Concrete Driveway Joints
Filling expansion joints helps:
- Prevent water infiltration
- Minimize slab movement and cracking
- Improve aesthetics of your driveway
- Extend the lifespan of your concrete
Common Mistake: Leaving joints open for too long invites costly repairs. Sealing is much cheaper than replacing cracked slabs.
Want to go a step further and refresh the whole surface? Check out our Sacramento driveway renovating options — perfect if cracks or stains are spreading beyond just the joints.
Tools and Materials You’ll Need
| Tool/Material | Purpose |
| Backer rod | Creates a base for sealant, saves on filler use |
| Polyurethane sealant | Flexible and long-lasting joint sealant |
| Caulking gun | To apply the sealant smoothly |
| Joint cleaner or blower | Removes dirt and debris |
| Utility knife or scraper | Removes old filler (if any) |
| Masking tape | For clean, neat lines |
| Gloves and safety goggles | Personal protection during the work |
Step-by-Step: How to Fill Expansion Joints in a Concrete Driveway
1. Clean the Joints Thoroughly
Use a blower or joint cleaner to remove dust, debris, and vegetation from the joint. If you’re redoing old joints, scrape out old sealant using a utility knife.
Pro Tip: Wash the area and let it dry for 24 hours before filling. Moisture can affect the bonding.
2. Insert the Backer Rod
Gently press the foam backer rod into the joint until it’s about 1/2 inch below the surface.
- Choose a rod diameter slightly larger than the joint gap
- This helps prevent 3-point bonding and saves sealant
3. Apply Masking Tape (Optional)
Tape the edges of the joint to prevent sealant overflow and ensure a clean finish.
4. Fill With Sealant
Using a caulking gun, apply your polyurethane or silicone-based sealant over the backer rod. Move slowly to avoid air bubbles.
Note: Avoid self-leveling sealant on sloped driveways—it can run out before curing.
5. Smooth and Finish
Use a spoon or jointing tool to smooth the surface of the sealant. Remove masking tape before the sealant skins over.
6. Let It Cure
Allow at least 24 to 48 hours of curing time before driving or walking over it.
Not sure if DIY is enough? Call Sacramento Concrete Contractor at 877-845-5360 for expert help with expansion joint repair in your concrete driveway!
FAQs and Related Queries
Can you fill expansion joints without a backer rod?
Yes, but it’s not recommended. The backer rod improves durability and helps you use less sealant.
What’s the best sealant for driveway joints?
Polyurethane sealants offer the best balance of flexibility, adhesion, and longevity.
How often should expansion joints be resealed?
Every 3 to 5 years, or if you notice cracking, shrinking, or gaps.
DIY or hire a pro?
DIY is doable for short driveways and basic sealing. Call a pro if joints are wide, deep, or damaged.
Final Thoughts
Filling your concrete driveway’s expansion joints is a simple DIY project that protects your investment and enhances curb appeal. Whether you’re using a backer rod and polyurethane sealant or hiring a contractor, doing it right pays off in the long run.
If you notice widespread cracking or movement, our Sacramento fissure restore services can help stabilize the slab before sealing or resurfacing.
