A type of sand-cement slurry (called “mud in industry”) can be used to fill voids under concrete slabs. This mixture of sand, cement and water is pumped through holes drilled in a slab base to fill the voids below. In the past, filling the gaps under concrete meant only one thing: more concrete. Concrete gap filling simply plugged the gaps with more of the same materials, and although this method is still in use, with varying degrees of success, the technology has evolved.
The procedure involves first drilling penny-sized holes in the slab. The gap filling foam is then injected through the holes and under the slab. As the foam expands and spreads, it not only fills existing voids, but also lifts and brings the slab to similar conditions. There you have it, people, everything you need to know about filling a void under a concrete slab.
Again, voids under concrete slabs are very dangerous, especially if there are walls and more floors above, so you should make sure to correct the problems as soon as possible. If the broken section is still intact, often professionals simply lift the tile and replace the missing substrate. This is typically done with expandable polymer foam, inflatables, or jacks. Some companies prefer expandable foam, as it may be the easiest, but it requires special tools and training.
This is done by drilling small holes through the slab and directing the liquid foam into the vacuum. As the foam cures, it also expands and applies upward pressure to the tile, lifting it up. This method also uses foam as a substrate, so often no other support or filler is required. Once the foam cures, the top layer of the surrounding soil is properly tilted away from the slab to prevent the problem from recurring.
An alternative method to fill the void under the concrete slab is to repair discrete sections of the damaged concrete slab. Keep in mind that a slab lift pump is a machine designed specifically for this job, to deliver fill material to voids under concrete slabs. However, for this case, when the vacuum is already large, the concrete slab will be prone to breakage, therefore, it is best to break the defective area of your concrete slab with jackhammers. A vacuum under your concrete when not repaired immediately will cause extensive damage to the slab that lifting the slab or repairing the sectional slab can repair the concrete.
Filling a gap under a concrete slab or sidewalk is critical to the structural integrity of concrete. You can always buy a specialized concrete gap filler, although these tend to be quite expensive.