Why Concrete Sinks and How To Lift It

If concrete around your home is sinking, you might be wondering why it’s happening and how to fix it.

In short, what’s likely happening is that the weather is eroding the soil beneath your concrete, and the weight of your concrete is dragging it deeper into the ground. Because concrete isn’t flexible, it cracks and looks ugly.

The negative result of all this is a major hit to your property value.

At Tar Heel Basement Systems, we use PolyRenewal™, a polyurethane foam injection to quickly and effortlessly lift and level concrete. In this article, we’ll dig deeper into the causes of your sinking concrete and what you can do about it.

Over time, the concrete structures around your home will inevitably begin to sink. Simply put, the causes of sinking concrete have to do with local weather, soil composition, the weight of the concrete itself, and just how much you use your concrete.

In specific terms, here’s why it sinks:

• Soil consistency matters. Soils that “congeals” versus looser ones determine how well they will hold up under the weight of concrete and also how well they interact with water. For example, clay soil expands when wet and shrinks when dry while sandier soils are more prone to washing out, both of which lead to sinking concrete.
• Repeated soil expansion due to moisture and temperature changes, can weaken the soil and cause it to compact under the weight of concrete, leading to visible damage.

• Soil Washout or erosion from underneath concrete slabs is more likely in sandy soil and can lead to hollow spots under the concrete.
• Droughts shrink the soil around and underneath your concrete
• Excess rain and poor drainage often contribute to soil washout.
• Invasive tree roots can displace soil beneath concrete.

• Excessive weight from cars or heavy décor can compact already weak soil, exacerbating the problem.
• Improper soil preparation before pouring the concrete can result in the soil washing out earlier.
• Improperly poured or mixed concrete during construction can compromise the durability of the concrete itself.

• Cracked Concrete: Cracks in your porch, driveway, or sidewalk can signal soil shrinkage, compaction, or settling. Weather, water, or soil type changes can cause shifts in the earth, leading to cracks in the concrete.
• Uneven Concrete Slabs: Unstable soil can cause concrete slabs to move, collapse, sink, or bulge. This creates uneven surfaces that can be unsafe. Excess pressure on these slabs should be avoided to prevent further damage or injury.
• Hollow Sounds Under Concrete Slabs: A hollow sound when tapping on a concrete slab can mean soil issues. This sound usually indicates the presence of voids between the slab and the soil.
• More Frequent Water Puddles: Soil that has shrunk, compacted, or settled may not absorb water well, causing puddling around concrete or dampness nearby. If stepping on concrete pavement brings water to the surface, it’s a sign that action is needed.

To repair damaged concrete, PolyRenewal™ is an effective solution. It stabilizes and levels the concrete, and due to its quick curing time, it also reinforces the slabs against heavy loads. PolyRenewal™ Injection Foam is lightweight yet strong, combating soil compaction and settlement. It’s waterproof and cures in just 15 minutes, providing a durable solution not affected by the elements that cause soil issues.

While mudjacking is sometimes suggested as a fix for soil-related issues, it’s a temporary measure that may exacerbate the problem. Mudjacking uses a mortar-based mixture which adds more weight to the soil, increasing the risk of soil compaction and settlement. PolyRenewal™ Injection Foam is a more efficient and versatile option for treating your concrete.

PolyRenewal™ is a polyurethane foam that is injected into specific areas of the concrete to fill any voids between the concrete and the soil underneath. This foam cures in just 15 minutes, effectively raising your concrete and allowing you to use your driveway, sidewalk, or pool deck again. This method is quicker and less invasive than alternatives like mudjacking or slab replacement, and it’s barely noticeable that any work has been done.

The complete process of our polyurethane injection involves:

• Penny-sized holes are drilled in the sunken concrete slabs.
• Injection ports are inserted into the holes.
• Polyurethane foam is injected into the hole where it will spread to fill voids.
• The foam cures in 15 minutes.
• The injection ports are then sealed and smoothed over.