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What To Do If Your Concrete SinksMay 25th, 2021 by
Concrete slabs may be solid, but they aren’t perfect. Over time, you may discover that your sidewalk, driveway or basement floor is cracked and uneven. This means the concrete is sinking into the soil. It’s a process sometimes called slab settlement.
Left unchecked, slab settlement can jeopardize concrete’s integrity. Spotting and fixing it early is ideal. There are all kinds of projects homeowners can do on their own. However, it’s best to turn to a concrete repair professional when you discover sinking concrete.
In this article, we’ll cover …
- How to tell if concrete is sinking
- Common conditions that lead to slab settlement
- What you can do on your own to limit damage
- How to find a professional to repair damaged concrete
How To Detect Slab Settlement
Cracks form in concrete slabs for all kinds of reasons. Slab settlement isn’t the only culprit. In fact, some concrete slabs are designed with control joints—grooved lines that crack before the rest of the slab. These serve as a way of managing the effects of stress on the concrete.
To identify slab settlement, you’re looking for widespread, uneven cracks. Uneven edges along cracks in concrete—or worse, sunken sections—are clear indications of sinking.
If the home’s foundation is sinking, you’ll see evidence inside the house, as well. Pay particular attention to door frames and windows. If these are no longer flush, your foundation may have shifted. Also look for cracked, bulging drywall, tilting chimneys, uneven stairs, and floors that are no longer level.
Concrete slabs are naturally prone to settling into soil. That alone isn’t cause for alarm. It only becomes a problem when the settlement occurs unevenly or rapidly, putting stress on the concrete.
Why Is My Concrete Sinking?
Concrete sinks because of changes in the soil’s capacity to hold it up. There are a number of ways that this can occur.
Poor Soil Compaction
Soil compaction matters most when construction begins.
Generally, a plate compactor is used to stamp down soil before concrete is poured on top. However, deeper layers of soil may not be fully compacted in this process. When the deep soil begins to settle, it takes the topsoil down with it.
Loose, loamy soil is especially prone to this phenomenon.
Also, the ground is leveled and filled during construction. If the fill material doesn’t get compacted sufficiently, it opens up the possibility of slab settlement later.
Soil Expansion and Contraction
Soil that’s rich in clay absorbs water more readily. This causes it to change in volume as it does. The degree of change is called the shrink-swell index. Soil with high shrink-swell index is known as expansive soil.
Dramatic changes in soil volume (due to high clay content or extreme changes in soil moisture) can strain concrete. This can result in damage.
Maturing trees and vegetation also affect soil shrinking and swelling. Tree roots naturally displace soil and drain moisture. A tree growing near your driveway may spread its roots underneath, causing problems for the concrete.
An abundance of water can affect soil integrity by causing erosion. This is especially true after flooding and heavy storms or due to a leaking water line.
Poor drainage can be another issue. For example, when a surface slopes towards the slab rather than away from it. This allows erosion to form voids in the soil, causing the soil and slab to settle.
Slab settlement, in turn, can change drainage patterns for the worse, encouraging more void formation and compounding the problem.
In colder regions where the subsurface temperature dips below freezing, water in porous soil can freeze into “ice lenses.” Ice Lenses are wide ice formations kept relatively flat by the weight of topsoil.
Despite that weight, the expansion of ice lenses is enough to force higher layers of soil upward in a process called frost heaving.
Frost heaving strains concrete on the surface in the same way soil expansion does. Roads and foundations in susceptible climates experience significant damage caused by frost heaving.
A combination of frost heaving and slab settlement can wreak havoc on your driveway or foundation.
DIY Concrete Maintenance Solutions
For minor cases of slab settlement, you have some options for remedying the situation yourself.
Replace the Slab
The most apparent is to remove the damaged slab, wholly or in part. You’ll then need to compact and fill the underlying soil before pouring new concrete.
Don’t do the first step without the second. Replacing damaged concrete without doing something about the underlying soil will only result in more issues.
Take the time to ensure the surrounding land has good drainage, too.
Also, pouring concrete takes time and this solution can be excessive if the slab remains largely intact.
Repair the Slab
There are ways to lift a concrete slab without removing it.
The most common method is called mudjacking or slabjacking. This involves drilling one or more holes and pumping filler material through them to push the slab up from below. Commonly, a mixture of sand, local soil, fly ash, and Portland cement serves as the filler.
Other possible lifting materials include limestone grout, pure sand or gravel, and expanding polyurethane foam.
Most of these materials—especially the soil slurry—can be readily obtained by DIYers. Provided you choose the right filler, this can be a relatively easy and inexpensive option.
Foam filler has the advantage of being lightweight and providing extra lift, but it requires unique equipment to mix and pump it.
When You Need Professional Help
A heavily sunk slab can be difficult, if not impossible, for homeowners to lift themselves. This is especially true if the underlying problems are extensive.
Additionally, slabjacking equipment is not easily accessible to everyone. Plus, if these repairs are done improperly, the process can create more damage and even make a mess of the surrounding area.
Fortunately, foundation and concrete repair specialists have the necessary equipment and supplies.
They can also offer additional solutions that you wouldn’t be able to attempt on your own, like installing helical piles to support the slab.
Be sure to do a thorough search for the best local concrete specialists in your area before contracting with anyone.