A slab of concrete can sink for many reasons, and with different results. The culprit is commonly underground water that shifts the gravel and sand foundation below your concrete. When this happens, there is nothing left to support the weight of the concrete, causing it to sink. The issue can also arise if the right materials or techniques weren’t employed during the initial concrete installation. Whatever the cause, when it comes time to fix the problem, you have a decision to make.
The question is whether the sunken concrete slab on your sidewalk, driveway, or patio, needs a concrete repair or a complete replacement. The decision will come down to three issues: cost, severity of the damage, and your capabilities.
When it comes to cost, you could be looking at less than $20 or over $5,000. A minor repair entails patching holes or cracks. However, If the damage is extensive, there are a few options regarding how to go about the repair so it is best to have a professional come offer advice on how they would handle the situation. Collect bids and information from a few companies so you can compare their suggestions to help you develop a budget.
Severity of Damage
Concrete is very heavy. That makes it susceptible to sinking and cracking as the earth moves below it. It also makes it difficult to work with. Even hauling away broken concrete in a wheelbarrow is perhaps a job for a stronger back. Minor repairs are easier to tackle, though.
Concrete that has sunk slightly in one area may result in nothing more than a crack. When this happens, simply head to the home improvement store for easy-to-find concrete repair supplies and wrap the job up yourself. Be aware that this type of repair will likely be somewhat temporary, which is fine if you’re moving, it’s a space you don’t use often, or you have plans to replace it in the future. If the cause of the sinking concrete stems from poor water drainage or other issue, it will need to be dealt with eventually as time and budget allows. In the meantime, a patch might be a suitable solution.
On the other hand, a concrete surface that is clearly broken up due to sinking will need to be completely removed and reinstalled. Similarly, an entire slab that sits well below where it should will need some major work as well. Repairing or replacing severely damaged concrete will require heavy equipment and heavy lifting. There will also be the added cost of extra materials. You can hire someone to do this work or create a plan to do it yourself. Just be realistic about what you can handle.
Once you know how deep the problem goes, you can plan for the repair or replacement. In addition to surface repairs, another option is to lift the slab and replace the foundation. This typically is only a solution for smaller sections of concrete as attempting to lift an entire driveway isn’t possible without causing more damage. Lifting even a small slab requires heavy equipment so you’ll have to decide if can access and maneuver the machines to lift the concrete.
Then replace or add to the subgrade materials. The initial materials may have been inadequate, such as fine dirt, so you’ll be hauling in gravel and sand in its place. You may even need to remove materials before the upgraded materials can be placed. When the materials are set, firmly compact the subgrade before replacing the concrete slab.
For a sunken concrete surface that can’t be repaired with a topcoat fix or foundational reinforcement, a complete replacement is your only option. This involves the same foundational steps of hauling in suitable materials and compacting them, but requires many additional steps as well. You will need to break up the original concrete and remove it from the space. This can be done with a jack hammer or heavy equipment. You may also need to haul away inferior sub grade. At that point, add new materials and compact. Then build the frames for the concrete and pour. Finish and seal your concrete to complete the job.