Why is pressure grouting so important after a slab foundation is raised?
If the concrete slab is raised, especially over 2 inches, it leaves a large void under the slab. The slab was not designed to act as a bridge member, supported at each end, and there is a danger the slab will sag into that void, in the future, if not supported in the middle. The slab was not designed to act as a bridge member, or it would have had a lot more steel reinforcement and would have been poured a lot thicker. Therefore it is important to pump a concrete/soil mixture under the slab, with pressure to fill the void sufficiently. But that is not the main reason pressure grouting is so crucially important after raising the foundation slab. The pressure grouting mud will SEAL OFF the void from moisture penetration under the slab. Ponding water, that will pond in the large void created by lifting the slab, will accumulate and create foundation problems in the middle of the slab. Usually this will occur in the first 2 years after the slab is raised. Many foundation contractors can of
