If you’ve ever noticed those gaps between your concrete slabs starting to collect debris or weeds, it’s probably time to seal your expansion joints. Proper sealing not only keeps your concrete looking neat but also prevents costly damage down the track. Those gaps aren’t there by accident, they’re designed to allow your concrete to naturally expand and contract as temperatures fluctuate without cracking.
Understanding Expansion Joints and Why They Need Sealing
Expansion joints are intentional breaks or gaps between concrete slabs that allow individual sections to move independently. Without these joints, the natural expansion and contraction of concrete would cause excess stress, leading to cracks and breaks. They’re essential, but when left unsealed, they can create problems.
Ever noticed how water seems to find its way under your concrete during heavy rain? When expansion joints are left open, rainwater can seep through and erode the soil underneath, causing your concrete to settle, sink, or even heave upwards over time. Not to mention, those moist gaps make perfect homes for weeds to take root.
Choosing the Right Sealant for Your Joints
Walking into Bunnings or your local hardware can be overwhelming with all the options available. Let’s break it down for you.
Polyurethane Sealants
These are your go-to option for most expansion joint sealing jobs in Australia. Polyurethane sealants offer excellent flexibility, durability, and resistance to environmental stress. Popular brands include:
- Sikaflex Pro+, designed specifically for movement and connection joints in concrete and masonry facades [1].
- Selleys Flexiseal, a fast-curing polyurethane that’s waterproof and suitable for both indoor and outdoor applications [2].
- RLA Flex-Pro, which offers a total joint movement capability of 50% (±25%) [3]
Silicone Joint Sealants
For joints between concrete and asphalt, products like Nitoseal SC820 provide excellent adhesion and can accommodate large joint movements. They’re particularly good for road and pavement applications.
Polysulphide Sealants
Two-component sealants like Sika Polysulphide are excellent for joints where large movement is anticipated. They’re chemically resistant to water, fuels, oils, and solvents, making them ideal for driveways and areas exposed to chemicals.
Materials You’ll Need
Before you start, make sure you’ve got everything on hand:
- Your chosen sealant
- A caulking gun (manual or pneumatic)
- Backing rod of appropriate diameter
- Utility knife
- Stiff bristle brush
- Leaf blower or vacuum
- Masking tape (optional but recommended
- Smoothing tool or spatula
- Protective gloves
- Cleaner or solvent for cleanup
I’ve been in the building game for 15 years, and I can tell you that preparation is everything when it comes to sealing joints. Don’t skimp on the backing rod, it’s not just filler. It creates the proper depth for your sealant and allows for that crucial hourglass shape that gives your joint the flexibility it needs.
Step-by-Step Guide to Sealing Your Concrete Joints
Step 1: Clean the Joint Thoroughly
First things first. Your joints need to be clean as a whistle. Sweep out any pebbles, dirt, or loose debris. For a deep clean, use a concrete cleaner and a stiff bristle brush to scrub the surface. Rinse thoroughly and let it dry completely before moving forward, most sealants won’t adhere properly to damp surfaces.
Step 2: Remove Old Material and Prepare the Surface
If you’re resealing, you’ll need to remove any old sealant. Use a grinder with a round disc to vee out the edges of the joint, then vacuum all the debris and dust. For better adhesion, roughen the edges with a pole sander.
Step 3: Install Backing Rod
This is crucial. Press backing rod into the joint to control the depth of your sealant. The rod should be about 30-50% wider than the gap so you can jam it down a couple of inches. This creates the correct profile for your sealant, ideally, the width to depth ratio should be 2:1 for optimal movement capacity.
For very deep joints (5-6 inches), fill the bottom with sand first, then add your backing rod on top.
Step 4: Apply the Sealant
Now for the main event. Cut the tip of your sealant nozzle to match the width of your joint. For horizontal joints, use a self-leveling polyurethane sealant like QUIKRETE Self-Leveling or Sikaflex. Move the nozzle slowly along the joint, allowing the sealant to settle naturally.
For vertical or sloped joints, you’ll want a non-sag formula instead. These won’t run down your sloped driveway. Apply the sealant in a continuous bead, ensuring full contact with the sides of the joint.
Step 5: Smooth the Sealant
If you’re using a non-self-leveling product, you’ll need to tool the sealant. Use a smoothing tool or the back of a spoon to press the sealant into the joint for better contact with the sides. This step is critical for ensuring proper adhesion and a neat finish.
Step 6: Clean Up
Immediately clean up any excess sealant with a commercial solvent or a citrus-based cleaner. If you’ve used masking tape, remove it now while the sealant is still wet.
Special Considerations for Different Situations
Sloped Driveways
If your driveway has a significant slope, avoid self-leveling sealants as they’ll just run downhill. Instead, use a non-sag polyurethane sealant that will stay put where you apply it. Products like Pecora 301NS or similar non-sag highway joint sealants are perfect for these applications.
Wide Joints
For joints wider than 12mm, follow the 2:1 width to depth ratio. If your joints are exceptionally wide (around 2 inches), you might need to double up on the backing rod before applying your sealant.
High Traffic Areas
In areas with vehicle traffic or high foot traffic, look for sealants specifically designed for these conditions. Sikaflex PRO-3 Purform PowerCure is an accelerated polyurethane sealant made for floor joints and civil engineering applications.
Maintenance Tips
Your sealed joints won’t last forever. Even the best sealants will eventually wear down from UV exposure and weather conditions. Check your joints annually for signs of deterioration or separation. Catching problems early means a simple touch-up rather than a full replacement job.
I remember working on a beachfront property in Sydney where the harsh sun and salt air degraded standard sealants within a year. We switched to a high-UV resistant polyurethane, and five years later those joints were still going strong. It’s all about choosing the right product for your specific conditions.
Sources:
[1] https://www.bunnings.com.au/sika-310ml-grey-concrete-sikaflex-pro-polyurethane-sealant_p0083588
