Sunken concrete is easy to put off. It is also a trip hazard, a drainage problem and sometimes an early warning about the soil under your house. Here is how to judge whether yours needs attention.
Fix it soon if
- There is a vertical offset at a joint. One slab sitting higher than the next is the classic trip hazard, and it tends to worsen.
- It now slopes toward the house. A driveway or patio tilting inward routes storm water straight at your foundation.
- Water pools on it. Standing water on a slab means it has lost its drainage slope.
- A garage slab has dropped away from the foundation wall. That gap lets water in.
- It is still moving. Visible change over a year or two means the soil below is unstable.
You can probably wait if
- Hairline surface cracks with no height difference across them
- Isolated spalling or surface flaking from age, salt or freeze-thaw
- Cracks that have stayed the same for years and do not affect drainage
Why slabs sink here
Almost always a void below. Central Missouri clay shrinks in drought and leaves gaps. Poorly compacted fill settles over time. Water running under the edge of a slab washes fines out from underneath. The concrete itself is usually fine, it just lost what was holding it up.
Repair versus replacement
- Lifting. If the slab is structurally sound and simply settled, it can be raised by filling the void beneath and bringing it back to grade. Faster and less disruptive than tearing out.
- Replacement. Makes sense when the concrete is badly broken, crumbling or cracked into many pieces.
Deal with the cause too
Lifting a slab without addressing why it sank means you will be back. If a downspout is washing soil from under the driveway edge, that needs correcting at the same time or the void reopens.
When a sunken slab signals something bigger
A patio settling on its own is usually just the slab. A patio settling on the same corner where your doors have started sticking is a signal about the soil supporting your house. Worth having someone look at both together.
We handle slab and drainage work throughout Warrensburg and Central Missouri.
Not sure what you are looking at? We do free inspections across Warrensburg and the surrounding Johnson County area, and we will tell you honestly if you do not need work done. Call (816) 718-3385 or request an estimate.