A sunken sidewalk panel or driveway section is one of the most common calls we get in spring, after frost heave season reveals what the freeze-thaw did to the subbase. The question is always the same: mud-jack it or replace it? The honest answer is: it depends on the condition of the slab itself, not just whether it's sunken.
Mud-jacking — or slab lifting — works by drilling 1.5-inch holes through the slab, pumping a Portland-cement grout slurry beneath it to fill voids and float the slab back to grade, then patching the drill holes. It costs $400–$1,800 depending on area and access, against $8–$14 per square foot to replace. When it works, it's a great outcome — fast, non-destructive, and a fraction of replacement cost.
When mud-jacking works
Ideal candidates: slabs that have sunk uniformly due to soil compaction or subbase void, but are otherwise structurally intact — no cracking through the slab thickness, no delaminated surface, no exposed aggregate from scaling. A single sidewalk panel that dropped 1.5 inches after a tree root was removed is a perfect mud-jack candidate. We drill two or three holes, pump the slurry, and watch it come up to grade in twenty minutes.
When it doesn't
Mud-jacking adds weight to the slab — roughly 100 lbs per cubic foot of grout pumped in. If the slab is cracked through, that added weight often opens the cracks further, or the slab lifts unevenly and you end up with a worse trip hazard than you started with. If the surface is scaling or the slab is visibly thin (contractor skimped on thickness at original pour), lifting it isn't fixing the structural problem. And if the void below the slab was caused by ongoing water erosion — a broken downspout, poorly graded landscaping — lifting the slab is a temporary fix that will sink again within a couple of seasons unless you address the water source.
Our assessment process
At every site visit for a potential mud-jack, we tap the slab with a hammer (hollow thud versus solid ring tells us how much void is present), probe the crack pattern, and ask about drainage and any recent soil disturbance. If the slab passes, we recommend lifting. If it doesn't, we'll tell you why and quote replacement — knowing we do both kinds of work, we have no incentive to push one over the other. The goal is the right answer for the slab in front of us.