Sunken concrete: lift it or replace it?
A stoop leaning toward the house, a driveway that dropped by the garage, a sidewalk panel sitting an inch low. Sometimes lifting it is the right fix. Sometimes it's money down the drain.
Why concrete sinks around here
Concrete is heavy, but it's only as solid as what's under it. Around Omaha, three things cause most of the sinking we see:
- Backfill. The ground right next to a house got dug out and filled back in when the house was built. If it wasn't packed down well, it keeps settling for years, and stoops and patios go with it.
- Water. Downspouts and sump lines that dump next to a slab soften the ground or wash it away. Up on the bluffs, soaked loess can drop all at once.
- Age and roots. Old slabs poured right on dirt, and tree roots that lift one side and leave the other.
Lifting a slab
If the concrete is still in one piece, it can often be lifted back where it belongs. There are two common ways to do it. Mudjacking pumps a cement slurry under the slab through holes about the size of a quarter. Foam lifting does the same thing with polyurethane foam through smaller holes. Foam is a lot lighter, which helps on soft ground, and it costs a little more.
Either way it's usually a few hundred dollars up to a couple thousand, and you can walk on it the same day. Compared to tearing it out and pouring new, that's a good deal when it fits.
When lifting doesn't make sense
Lifting won't fix a slab that's broken into pieces. You'd just have broken pieces at the right height, and they'll keep moving on their own. It won't help much if the concrete is crumbling or flaking all over, either.
And it won't last if whatever caused the sinking is still going on. If a downspout is still dumping water under the slab, it'll sink again.
How we decide
When we come look, we're checking a handful of things. Is the slab in one piece? How old is it and what shape is the surface in? How far has it dropped, and is it still moving? Where's the water going?
If lifting will do the job, that's what we'll recommend. It costs you less and it's a lot less of a mess. If the slab is past that point, we'll say so, and when we replace it we'll fix the reason it sank. Usually that means packing the base properly and pointing the water somewhere else.
Don't let a stoop go too long
A stoop or patio tipped toward the house sends rain straight at your foundation. It's rarely an emergency, but it's worth fixing before it turns into a wet basement. Call (531) 236-6623 and we'll come take a look.