There are typically three things that may happen to the soil underneath your concrete that can cause concrete slab sinking.
Water is great at finding its way into places it’s not supposed to be. Even if there’s the tiniest leak in a concrete surface, water from the rain, plumbing leaks and even just condensation can make its way underneath that surface.
Over time, this water will start to wash away the soil piece by piece. This typically doesn’t happen overnight unless there’s an extreme weather or plumbing condition. However, no matter how slowly it erodes, you’ll start to notice at some point.
Eventually, there will be less soil underneath the concrete supporting it. As the amount of soil diminishes, the slab will start to sink into the empty space underneath. That’s why you’ll start to see concrete slab sinking.
Poorly Compacted Soil
During construction, the construction crew pours the concrete over the soil. To prepare the ground for the concrete, the crew needs to pack the soil down tightly. This forms a good base for the soil to hold onto and stay stable on.
However, if the crew didn’t compact the soil tightly enough, it can start to compress because of the weight on top of it. The concrete is essentially sinking because of its own weight and any weight you’ve placed on it.
This is especially dangerous if it’s happening in your basement. A sinking basement floor typically signifies that there’s something wrong with your home’s foundation, and that can lead to many problems throughout your home.
Moisture Content Changes
The weather moves through cycles of wet and dry naturally. It’s normal for soil to be wetter, then drier, and to repeat that process. Unfortunately, while it’s natural, it’s not great for the concrete resting on top of it.
When soil absorbs moisture, it becomes bigger. When it dries out, it becomes smaller. This expanding and contracting process exerts pressure on the concrete above it, and that can lead to sunken concrete over time.
This can be especially obvious if the concrete is on a type of soil that expands or contracts more significantly than other types of moisture. It should rest on a more solid type of soil if you want to make sure it lasts a long time.