My 12 x 14 ft concrete patio is sinking in the middle towards the house.

Cathy F
by Cathy F
It has sunk about 2 inches in the last 6 to 9 months; the slab is about 18 inches to 2 feet above the surrounding ground. The house is 43 years old, so I find it hard to believe that is just now getting around to settling. We've had a huge problem with chipmunks. I know they've tunneled underneath the patio as we seen their holes. Can we just level out the surface or do we need to inject concrete to raise the slab back to level? What's the likelihood that it will crack down the middle? I don't know how much rebar was used in construction. Any thoughts?
  18 answers
  • As the patio sinks it allows for water to drain towards the lower side, (house) and will continue to drop. What happens even if the house is old is that the soil that surrounds the home against the foundation is never compacted for fear of foundation failure. in your case it sounds as though they raised the soil to to bring the patio up to the final level it was set at. Because of the rains we have had this past year this water has caused some movement of the soils under the slab to shift which can cause the patio to drop. As far as the chipmunks causing this. Yes and No. Typically they do not do that kind of damage as their holes are pretty small. But the very fact that holes are under the slab that will allow for water to enter this just sped up the process of the settlement. There are a few things that you can do to stop and fix this issue. One is of course tear it out and start again. Another would be to Mud Jack the slab back up into place. However you must first do something about the erosion that most likely is taking place around the outside edges of the patio. Otherwise the soil will erode again and the slab will drop once again. Mud Jacking is performed by drilling a series of holes of about 1 inch in size through the slab. A special tool that resembles a wheelbarrow that has a pump attached and a nozzle attached to that is placed into the hole and a slurry of cement and soil is pumped below the slab. The hydraulic action of this pumping lifts the patio a little bit at a time as they move from hole to hole until the slab is back up to its proper location. This procedure fills any voids that may have occurred because of wash out and because of the cement added stiffens the soil so it does not wash away as easy. Its a bit expensive, but if done correctly will work fine and the end cost is much less then tearing out the patio and dealing with all of that mess.
  • JL Spring & Associates JL Spring & Associates on Oct 13, 2011
    That could do the trick unless you've gotten on top of a sink-hole and then, there's no telling how much cement you'll need. I wouldn't spend too much time standing around in the middle though! First hole I'd drill would be almost dead center and get a probe bar down there to see if there's suppot beneath. Play it safe and tie a rope around your middle to a nearby tree...I'm not kidding, those things can collape pretty darn fast...I've seen cars swallowed up in an instant in Florida from weakened road support. Best to you, prayerfully, Woodbridge is on it. Find a local member/contractor here on HomeTalk that works in your area by using the search buttons top and left! JL
  • I did a home inspection a few years ago and the buyer was worried about a crack in the garage floor. When I see these I use my metal probe that I use for termite evaluations and tap on floor and listen for hollow sounds. I determined that there was one in the middle of floor and suggested that further evaluated. The contractor came over and drilled a hole in the middle of the floor and put a two foot metal rebar rod in the hole, then a six foot one. Then a eight foot one before he hit something that sounded like metal. They jacked up the floor and found an old Volkswagen buried under the floor of the garage!. After several yards of stone and a new cement floor all is fixed. You never know what you will find below cement.
  • KMS Woodworks KMS Woodworks on Oct 14, 2011
    Woodbridge....A buried VW...that a new one for me...
  • Yea, no one could figure out why it was there. Owners even had police there in case there was a body inside. Turns out just a junker that they needed to get rid of.
  • Amazing.....mostly we see builders here filled in with construction debris, stumps and the like before building on the lots....over time the stuff decomposes and the homeowner has a problem. I so wish you had pics or a video of the car.....unreal!
  • JL Spring & Associates JL Spring & Associates on Oct 15, 2011
    So That's where Herbie's been all these years! Sure Jim Hoffa didn't drive it inta th' hole?!;o!
  • KMS Woodworks KMS Woodworks on Oct 15, 2011
    Being from Michigan originally ...the story of where Jimmy is.... is buried deep in the concrete foundation of Detroit's Renaissance Center ....if Jimmy was from New York....he'd be out in the Meadow lands somewhere
  • Cathy F Cathy F on Oct 15, 2011
    Any idea of the chance that it would crack in two? My husband just wants to level it with cement on top, but I don't think it addresses the problem as to why it is suddenly sinking after 42+ years. Pretty sure there's no VW as I've been in the house since it was built.
  • JL Spring & Associates JL Spring & Associates on Oct 15, 2011
    I wouldn't try to pour over without finding out the why! Can you find an inspector near you that has portable Ultra Sound equipment. May be able to determine if there's dangerous sink hole activity...JL
  • Putting cement on top will do nothing to the patio other then ruin it as the coating on the top will come off the older cement under and begin to chip away. It could crack in two, or even worse. You need to address the cause and that can not be done using a band aid type of fix. What your husband is proposing is what low end house flippers would do because they do not care what happens after they sell.
  • KMS Woodworks KMS Woodworks on Oct 16, 2011
    A month or so ago I worked on a place where the back slab of a home had sunk a good 6" along the back and had cracked in many places. There was a cheesy sun room of sorts installed on this slab and the walls were all out of level creating many problems. The owner wanted a cheap cosmetic improvement so parts of the slab were demo'd and piers were poured to support the porch a lower cost alternative he had me install a deck over the entire area. Obviously the best route would have been to completely demo the slab and either pour a new slab or construct the deck...since he was signing the checks...this is what we ended up with.
    comment photo
    comment photo
  • JL Spring & Associates JL Spring & Associates on Oct 16, 2011
    That's the best idea yet Kevin. Looks super and could always be screened back in if the bugs get to bitin'! JL
  • Joe Washington Joe Washington on Oct 17, 2011
    In a situation like this I think it's best to remove all doubt and get to the bottom of the problem, so to speak Don't cover it up with more concrete, you may have a sinkhole but at the very least the water that's going in there is creatng more problems. The deck idea isn't a bad alternative tho, if you can afford to ignore what's going on underneath and I don't think I would.
  • Cathy F Cathy F on Oct 21, 2011
    Thanks for all of the input. I think we're going to get someone out to drill in and check it out. Hopefully, it will hold off for a month or so until we can afford it.
  • and, if its a really big hole, I know someone with a VW they need to get rid of...
  • lol got to find another one. That one is taken.
  • Angela P. Ellison Angela P. Ellison on May 16, 2018

    I live in Batesburg,SC HAVE A POOL WITH CONCRETE DECKING IT HAS CRACKED I HAVE BEEN TOLD THERE IS SOME TYPE FOAM THAT WILL FILL back in & level it out is this true and if so do you know anyone that does this type work??