Void underneath concrete slab?

[Woodtourer]

Has an tackled this as a DIY project? I have ,what sounds like a hollow, underneath a garage slab.

[brianwelch]

Has an tackled this as a DIY project? I have ,what sounds like a hollow, underneath a garage slab.

I know of someone...My brother. Has a foundation repair business. Was called in by a realtor to take a look at a sinking basement slab. Opened up a portion of the floor to get a view...Found over 6' deep void under a portion of the house. The house had been built over an infilled mine shaft, pretty much dead center. I don't recall how many yards of fly ash was pumped in, but it was plenty...

[woodgrain]

Has an tackled this as a DIY project? I have ,what sounds like a hollow, underneath a garage slab.

We had that happen to a garage slab in a home we built years ago.  We just hired TerraFirma to inject concrete slurry under it. quick and easy - not cheap though

https://www.goterrafirma.com/

[Woodworm!]

Has an tackled this as a DIY project? I have ,what sounds like a hollow, underneath a garage slab.

It maybe legit, Chip and Joanna of HGTV fame had a house project built on a slab like that, and they found out that from an architect that it was made that way.

[blackhat]

A slab made to be over a void will have massive amounts of rebar in it and will sit on pilings.

[JDuke]

I have a friend that uses 2 part foam to fill and level concrete slabs.  Homes, businesses, Parking lots etcetera

The stuff he uses is a much denser version of the foam used for insulation 

It’s not cheap, but as long as the foam isn’t exposed to light it works really well.

[Robert Adams]

Ditto the foam use. It comes in big bags just like the little ones for fence posts but much bigger. It's commonly used for plugging mine shafts. That is if you have a hole in the slab to pour it into...

      There is also the foam injection which I could easily see that being done with the home 2 part kits to an extent. The kits would fill the void and may lift a little but not as much as the commercial ones with a pump that can force the foam in there.

[mike4244]

Has an tackled this as a DIY project? I have ,what sounds like a hollow, underneath a garage slab.

I have , large crack developed in a slab on a house a realtor wanted to sell. The cracks were 1/2" wide and the slab sunken about 1" in the center. Gasoline masonry saw made short work cutting the slab. I found an old cistern that was covered with Q decking and concrete poured over that. I cut the slab back 30" past the hole on each side. I installed  five  2x10"s 10'-0" long across the hole and nailed 1/2" plywood sheathing over it. I drilled 3/4" diameter holes 8" deep on 10" centers in the edge of existing slab. 16" lengths of # 5 rebars were driven into the holes. #5 rebars were then tied to the stubs. The unsupported area was about 4-1/2' wide by 6-0" long. I thru bolted an angle iron across the width and added two anchor bolts . Short leg of anchor bolt went into holes in angle. Long threaded end went between two 4x4's. I tied a bit of insulation around the bolts where they protruded thru the slab. The bolts were cut off with a torch next day. 
Probably could have eliminated the angle and bolts but I did not want to take a chance of the formwork sagging.
This was in 1969 , no problems since. 
You may be able to do this yourself, If the area is not to large and deep you can fill the hole , compacting the fill as you go.
Maybe just fill with concrete, depends on the hole size and depth.
The job I did was too large and deep, at least 20'-0" deep. 
mike

[Patsfan]

Has an tackled this as a DIY project? I have ,what sounds like a hollow, underneath a garage slab.

Just had the foam thing done on a property in FL.  (By a contractor.)



The foam is strong enough to lift driveways sections, slabs, etc.

Not sure what part of the country you are in  - that might help.