How to Fill Concrete Gaps
Maintaining concrete involves careful attention to expansion joints and gaps. Expansion joints are essential for preventing cracks and extending the concrete’s lifespan, while gaps are unintended spaces that can develop over time.
However, if either is left unfilled, it can lead to significant issues. Understanding how to fill concrete gaps correctly can save on expensive repairs and ensure your concrete remains in good condition long-term.
This page explains what you need to know about filling concrete gaps and joints, the materials to use, and the process to get the job done right. Let’s get started.
How to Fill Gaps Between Concrete
Filling gaps between concrete is vital for preventing damage, but there are a few things to remember. First, identify the type of gap: Is it an unintentional gap caused by damage or an expansion joint?
While both types require filling, the process involves subtle differences that must be considered. Here’s what you should know about concrete gaps and expansion joints:
What is a Concrete Gap?
Concrete gaps are unintentional spaces or voids that occur in concrete surfaces. They are caused by improper concrete mixing, pouring, or curing. Concrete gaps occur in many areas, including:
- Slabs and Foundation: Uneven settlement creates gaps between these structures.
- Cracked Concrete: Existing concrete may develop gaps due to weathering, erosion, or damage.
- Around Utilities: Gaps may form where pipes or conduits pass through concrete.
- Along Concrete Curbs: Gaps may develop due to weathering or ground shifting.
- Basement Floors: Gaps appear due to settling or moisture changes beneath the concrete.
- At Drainage Systems: Gaps may form where these systems intersect with concrete.
What is a Concrete Expansion Joint?
Concrete expansion joints are intentional gaps between slabs that accommodate natural expansion and contraction from temperature changes and moisture. They help prevent cracking and promote long-term concrete durability. Expansion joints are most commonly fond on:
- Sidewalks: Expansion joints allow for thermal expansion and contraction.
- Driveways: Expansion joints prevent cracking due to ground movement or temperature changes.
- Concrete Slabs: Patios, driveways, and sidewalks may have expansion joints to prevent cracking.
- Bridges and Roadways: Expansion joints accommodate movement due to temperature changes, weather, and traffic loads.
- Parking Lots and Garages: Expansion joint installation prevents large area cracks.
- Building Foundations: Large buildings, like skyscrapers and industrial facilities, have expansion joints to accommodate structural movements.
Materials For Filling Concrete Gaps and Expansion Joints
The size of the gap, the expected movement, and the environment determine the best material for filling concrete gaps and expansion joints. Here are a few popular options:
Small Gaps and Expansion Joints (1/4″ or Less)
Typically, you can fill concrete gaps and expansion joints smaller than 1/4 inch with caulk. This makes it possible to avoid using a backer rod. Some points may be wider than others, so always measure the gap first to ensure you use the proper filling material. Materials for smaller concrete gaps and expansion joints include:
- Self-Leveling Caulk: Flexible, self-leveling caulk suits smaller areas and provides a smooth finish.
- Epoxy: A durable, moisture-resistant two-component adhesive.
- Concrete Patching Compound: A pre-mixed material that fills and repairs minor areas.
- Sealants: Silicone, polyurethane, and butyl rubber sealants provide flexible yet durable filling adhesion.
Large Gaps and Expansion Joints (Over 1/4″)
Gaps and expansion joints larger than 1/4 inch may require a backer rod. All sections should be measured before the filling process. Materials for large concrete gaps and expansion joints include:
- Non-Sag Caulk: Thick, easy-to-control caulk ideal for larger areas. It requires smoothing but stays in place and works well with a backer rod.
- Backer Rod: This material creates a uniform base for caulk, preventing sinking and cracking, and ensures an effective seal.
- Expansion Joint Filler: A pre-formed foam or rubber material that fills and seals the area.
- Concrete Repair Mortar: A mix of cement, sand, and water that fills and repairs larger areas.
- Joint Covers: Metal or plastic covers that protect the area from weathering and debris.
The proper filling product for your project depends on the size and location of the gap or expansion joint and the specific application requirements. Contact a concrete professional to ensure long-term and effective repair.
Self-Leveling vs. Non-Sag Caulk
Self-leveling and no-sag concrete caulk achieve similar results; however, there are notable differences. Self-leveling caulk has a thin consistency, flowing freely into gaps without manual smoothing.
Non-sag concrete caulk is thicker and maintains its shape but requires manual smoothing. Many people use it with self-leveling caulk to add moisture resistance and shape retention.
Materials to Avoid When Filling Expansion Joints
Due to their limitations, avoid the following materials for filling expansion joints:
Grout and Mortar
Materials that lack flexibility, like grout and mortar or concrete overlays, are prone to cracking and crumbling as temperatures change. They are not suitable for filling expansion joints, where flexibility is crucial.
Wood
Wood was once considered ideal for filling concrete expansion joints due to its ability to expand and contract with moisture and temperature changes. However, it proved ineffective as a sealant, allowing water penetration and eventual wood rot.
Why Fill Concrete Gaps and Expansion Joints?
Filling concrete expansion joints and gaps between concrete is essential to prevent issues such as:
- Water Infiltration: Unsealed joints and gaps allow water infiltration, causing soil washout and erosion, settling, heaving, and potential structural damage.
- Weed Growth: Moisture promotes weed growth in joints and gaps, with roots eventually causing cracks or uneven concrete.
- Cracking from Freeze-Thaw Cycles: Repeated freeze-thaw cycles can cause cracks in unsealed joints and gaps, compromising concrete integrity.
Professional vs. DIY Concrete Repair
If you’re weighing the pros and cons between professional services and a DIY approach, consider the following:
- Professional Concrete Services: Concrete repair professionals ensure smooth and durable results. Professionals have the expertise and tools required to handle complex repairs and provide warranties for their work.
- DIY: Saving money with a DIY approach may seem cost-effective. However, DIY projects’ time, effort, and attention to detail often do not match professional quality, especially for more extensive or intricate repairs. DIY projects usually do not provide long-term results.
What is Polyurethane Foam Injection?
Polyurethane foam injection is a minimally invasive concrete repair method for uneven, sinking, or settling concrete surfaces. The environmentally friendly, waterproof foam gently lifts and levels slabs by stabilizing the soil beneath the concrete. Since soil is the leading cause of concrete damage, polyurethane foam injection is a highly effective, long-term professional solution for repairing uneven and sinking concrete.
Contact Groundworks for a Free Concrete Inspection
Filling expansion joints and gaps between concrete is crucial for maintaining your property and preventing costly repairs in the future. If you’re unsure about the best approach, contact Groundworks. We offer free inspections and no-obligation repair estimates to ensure peace of mind.
Concrete Lifting FAQs
Floor and wall gaps are aesthetically frustrating, but do they always indicate a serious concern? Is it possible that your floor and wall gaps could just be aesthetically annoying? Unfortunately, they are pretty much always caused by an underlying problem. Here are a few of the issues that could arise with floor and wall gaps.
- Foundation Settlement
If one side of the home has started to settle faster than another side of the home, the wall is going to have that same settling problem. However, the problem will mainly have to do with one side of the wall bearing more weight than the other. When this happens, a gap can open up on whichever side of the home doesn’t have settling problems.
Although foundation settlement can cause problems with wall gaps, that isn’t the worst that could happen. It can also lead to a variety of structural concerns, up to and including walls and floors collapsing. Fixing foundation settlement should therefore be a priority for you.
- Wood Rot
Are you experiencing wood rot or other waterlogged wood problems? If so, you may also have floor and wall gaps happening. Wood rot problems can cause the center of the floor to dip inward, often leading to gaps opening between the walls and the floor. It’s a key component of that “bouncy floor” feeling that some homes occasionally end up with.
Although wood rot is one of the more common problems to notice in this arena, other issues may cause similar symptoms. For example, mold and mildew both require a lot of water to grow and can develop on all sorts of organic materials. Regardless of the actual problem, any growths on your floor joists are an issue.
When you see a wall and floor gap, you might wonder if there’s only a problem when the gap is a specific size. How big does the gap between the wall and floor have to get before it’s a real problem that requires an expert’s help?
- Any Gap Is a Problem
Unfortunately, any wall and floor gap can be a problem. You should always take home problems seriously, whether those problems seem minuscule or seem extremely serious.
The moment you see a gap between the wall and floor, you should know that there’s a problem and start dealing with that problem seriously. Handling problems that revolve around gaps between the wall and the floor is the best way for you to make sure that you truly have enough structural stability for a healthy home.
- A Widening Gap Indicates That Things Are Changing
Although any gap indicates a problem, you have a problem on your hands if you notice a widening gap. That’s because when the gap gets larger and larger, it’s indicating that the underlying problem is continuing to get worse. For example, if a gap is happening because of foundation settlement, a widening indicates that the settlement is getting even worse.
If you notice a widening gap, you have a problem that needs to be fixed. Whether it’s foundation settlement, poor construction, moisture problems, or something else, you need to fix it to avoid other secondary problems that can be much worse. Talk to an expert as soon as possible to address the underlying causes.
Common problem signs indicating that your concrete may need to be lifted and repaired include cracks, heaving or sinking areas, or visible gaps between slabs. Unevenness can cause safety concerns, such as tripping hazards, and can also negatively impact the aesthetics of your property.
Shaye Glisson
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Disclaimer: “Concrete leveling” means the process by which cracked, uneven concrete is stabilized, and in many cases lifted, by means of PolyRenewal™ polyurethane foam. Groundworks does not guarantee that PolyRenewal™ can make your concrete perfectly level.