Before choosing the type of sealant you need, you must first determine the cause of your concrete's cracking. Cracks in concrete will have different causes depending on whether the concrete is indoors or outdoors.
Outdoor Concrete Crack Causes
Here are some reasons your outdoor concrete may crack or settle:
- Erosion: Poor yard drainage and improperly diverted downspouts can cause the base soils to erode, resulting in the slab settling or dropping.
- Improper Installation or Placement of Expansion Joints: Expansion joints must be correctly installed in colder climates to accommodate the natural expansion and contraction of concrete. Joints should be placed along walls and spaced every 12 feet for 4-inch outdoor concrete slabs to prevent cracking caused by thermal changes.
- Settlement Issues: Pouring concrete over disturbed or poorly compacted soil can lead to base failure and settlement. If this is the issue, the slab should be stabilized using techniques such as mudjacking or polyjacking before applying sealant.
- Frost Heave Damage: In cold weather, the soil beneath the concrete can freeze and expand, causing the slab to lift. When temperatures rise, the soil thaws and the slab settles again. This freeze-thaw cycle can cause significant damage over time.
Indoor Concrete Crack Causes
Since indoor concrete isn't affected by weather, diagnosing cracks is generally more straightforward. Here are some common causes:
- Shrinkage: Concrete naturally shrinks as it cures and dries. It can shrink by as much as 3/8 of an inch over a 25-foot span, potentially leading to cracks if not properly controlled.
- Settlement: As with outdoor concrete, improper soil preparation or unsettled ground can result in cracking.
- Heavy Loads: Heavy vehicles or forklifts placed on slabs not adequately designed to support them can cause structural damage and cracking over time.
Gaps or cracks in concrete allow water, insects, and other damaging elements to penetrate the structure. In winter, freezing temperatures can cause these gaps to expand. Sealing cracks prolongs the lifespan of the concrete and can save you money on future repairs.
To properly seal cracks in your concrete, follow the steps below:
Step 1: Clean and Prepare the Crack
Before applying the concrete crack filler, it's essential to prepare the crack to ensure proper adhesion and durability. Remove any loose concrete, dirt, old caulk, or debris using an electric grinder with a V-shaped blade. If a grinder isn't available, a wire brush or chisel can be used instead.
After cleaning, use a vacuum, blower, or compressed air to remove dust and debris. For deeper cracks, insert a backer rod or fill the bottom portion with sand to prevent the caulk from sinking too deeply.
Step 2: Select the Appropriate Concrete Caulk
Use a caulk specifically designed for concrete. It should be waterproof, flexible, and have strong adhesion to concrete surfaces. Silicone and polyurethane caulks are commonly used.
Self-leveling polyurethane caulk is preferred for horizontal surfaces because it spreads evenly without tooling. Non-sag caulks require manual smoothing but may be better suited for vertical applications.
Step 3: Cut the Caulk Tube Nozzle
Cut the tip of the sealant tube at a 45-degree angle using a utility knife. This angled cut allows for smoother and more precise application.
Step 4: Apply the Concrete Caulk Properly
Using a caulk gun, apply a consistent, thin bead of concrete caulking sealant along the length of the crack, ensuring it is filled.
With self-leveling caulk, be careful not to overfill the crack, as it can spread onto the surrounding surface.
For silicone or toolable caulk, smooth the bead immediately after application using a putty knife or your finger. For wider or deeper cracks, you may need to apply multiple layers, allowing each to cure before applying the next.
Step 5: Smooth the Caulk for a Clean Finish
Smooth the caulk using a caulking tool or a wet finger to achieve a clean, professional finish. This also ensures better adhesion.
To improve the appearance with self-leveling caulk, you can broadcast color-matched sand over the wet surface. After a few minutes, gently blow or sweep off the excess sand.
Step 6: Let the Caulk Cure Fully
Let the caulk dry completely before allowing any foot or vehicle traffic on the repaired area. Drying time varies based on the type of caulk and weather conditions. Always follow the manufacturer’s instructions for curing time.
Step 7: Seal the Caulk and Surrounding Concrete
Once the caulk has fully cured, apply a concrete sealer over the repair area. Sealing protects the caulk from UV rays, moisture, and other environmental elements, significantly extending the life of your repair.