There is something satisfying about watching a sunken slab rise back toward level. The crack closes a little, the door swings freely again, the puddle on the patio finds its way to the drain. I understand the appeal. But in my experience, the most useful conversation about slab lifting starts somewhere other than the slab.
Patio concrete versus the floor under the walls
It helps to separate the concrete outside the house from the concrete the house sits on. A walkway, patio or driveway section that has dropped is mostly a question of drainage, trip hazards and appearance. A slab-on-grade floor inside the house carries walls, and when it moves, the framing above it moves too.
Lifting is used for both, but the stakes differ. Outside, an imperfect result is usually tolerable. Inside, a lift that goes too far or too fast can crack finishes, rack door frames or stress plumbing beneath the slab. Our post on flatwork around Del Mar homes covers the exterior side in more depth.
Why the ground let it down
Before anyone talks about methods, it is worth asking what changed below. In Del Mar, the usual suspects are familiar: fill that was never well compacted, soils that soften when they stay wet, voids washed out by a leaking pipe or a downspout that empties beside the slab, and in the river valley, ground that is younger and looser than the mesa tops.
The California Building Code’s soils and foundations chapter describes when geotechnical investigation is called for and what it addresses, including questionable soils, expansive soils and compaction of fill. Not every slab lift needs a full investigation, but when the cause is unclear, guessing is expensive. A slab raised over a soil problem that is still active may simply settle again.
Grout pumped beneath the slab
The oldest approach drills holes through the concrete and pumps a cement-based grout underneath, filling voids and pressing the slab upward. It is sometimes called mudjacking or slabjacking. The material is heavy, which adds load to soils that may already be weak, and the holes tend to be larger than with newer methods. It can work well for exterior sections over a stable base where the main issue was a void.
Expanding foam injection
A newer approach injects a polyurethane material that expands beneath the slab. The holes are smaller and the material is light, which is attractive on soft ground. The expansion has to be controlled carefully, since too much can over-lift or crack the slab. Like grout, foam fills the space under the concrete; it does not by itself change the deeper soil that let the slab down.
When the support has to reach deeper
If the soil near the surface is the problem, filling the gap beneath the slab may not be enough. In those cases, support can be carried down to firmer material using piers, some of which allow the slab or footing to be raised as they are loaded. Helical piles are one such system, and ICC Evaluation Service publishes acceptance criteria, AC358, for helical pile systems. Push piers and other types fill similar roles. Our post on underpinning in Del Mar explains how those families differ.
Pier-supported lifts are usually more involved, often require design, and may call for special inspection under Chapter 17 of the Building Code. They are also the methods that respond to a settlement problem rather than its symptom.
Slabs that should not be drilled casually
Some Del Mar homes, particularly newer ones, sit on post-tensioned slabs with steel tendons cast under tension inside the concrete. Drilling blindly into such a slab can damage a tendon. Any lifting or injection on a post-tensioned slab should begin with locating the tendons. Interior floors may also hide radiant tubing, plumbing and electrical lines, so the same caution applies more broadly.
When replacement is the honest answer
Occasionally a slab section is so broken, or the subgrade so poor, that lifting it would only preserve a problem. Removing the section, correcting the base and drainage, and placing new concrete can be the more durable course, especially outdoors. The Residential Code’s foundations chapter speaks to base preparation and slab construction for new work.
Water, again
Almost every settled slab I have looked at near the coast had a water story: a gutter that dumped against the edge, planters that kept the soil soaked, or a pipe that leaked for a season before anyone noticed. Lifting without addressing that water is optimism rather than repair. The practical order is usually to find and correct the source, let things settle into a stable condition, and then lift. I also suggest a season of simple observation afterward. A few dated photographs of the lifted area, taken from the same spot after the first real rain and again after the first long dry stretch, tell you more about whether the cause was addressed than any single measurement taken on the day of the work. If the slab holds through both, the lift and the drainage correction were probably the right pair.
Permits and records
Interior slab work, pier installation and anything that touches structural support often involves the City’s building review. The City of Del Mar’s Building Services page is the starting point for understanding what a given project needs. Keeping the drill pattern, injection quantities and before-and-after elevations in your house file also helps the next owner, and the next contractor, understand what was done.
Factors that shape a lifting scope
Rather than prices, owners can think about the variables: the area of slab involved, interior versus exterior work, access for equipment, the depth to competent soil, whether tendons or buried lines must be located, the need for design and inspection, and restoration of finishes afterward. Our slab foundation repair and foundation settlement repair pages describe the broader picture, and we coordinate with licensed engineers as needed when design is required.
Before choosing a lifting method
If a slab at your home has dropped and you would like help sorting out why before choosing how, an evaluation is a sensible first step. We work throughout the City of Del Mar. Free Quote