How do you fill voids under a concrete garage floor?

https://www.youtube.com/watch?v=AwJwwSsax7k

What material is used as fill beneath the concrete slab?

A sand-cement grout can be used to fill voids under concrete slabs. This mix of sand, cement, and water is pumped through holes drilled to fill up the voids.

What is the best material to put under concrete?

Most concrete contractors want a mix of coarse and fine aggregate to create a compactable base that is going to be safe for settlement and drainage. Crusher run (a mix of crushed stone and stone dust) is one of the best base materials for concrete flatwork.

Is it good to put plastic under concrete?

Recently, though, research has shown that the old traditional layer of 6-mil Visqueen (polyethylene plastic) under the slab is seldom effective for two main reasons: Although it may seem water-tight, this grade of material allows a lot of water vapor to pass through.