# What Concrete Leveling (Polyjacking) Involves | Guide > How polyurethane concrete lifting works: injection ports, foam expansion, void filling, cure time, and the non-excavation benefit. URL: https://sanantoniofoundationrepair.net/guide/what-concrete-leveling-polyjacking-involves/ Last-Modified: 2026-09-16 Homeowner guide # What Concrete Leveling (Polyjacking) Involves How polyurethane concrete lifting works: injection ports, foam expansion, void filling, cure time, and the non-excavation benefit. Published September 16, 2026 · 4 min read ![Technician injecting polyurethane foam through a port in a sunken driveway](/images/featured/technician-injecting-polyurethane-foam-through-a-s.webp) ## The Method in Short Small ports are drilled through the settled slab. High-density polyurethane foam is injected through them. It expands underneath, filling the void that let the slab drop and then lifting the concrete back toward grade. Ports are patched flush and the surface goes back into use, usually the same day. That is polyjacking, and it is non-excavation lifting: nothing is dug up, nothing is demolished, and there is no spoil pile in the yard. Our concrete leveling [/concrete-leveling/ →](/concrete-leveling/) page covers the service in full. ## What Happens Step by Step **1\. Assessment.** Slab thickness and condition, the size and shape of the drop, likely void extent, utilities beneath the slab, and the original drainage intent. This determines whether lifting is even viable, which is covered in our guide on which concrete surfaces can be leveled [/guide/which-concrete-surfaces-can-be-leveled/ →](/guide/which-concrete-surfaces-can-be-leveled/) . **2\. Port layout.** Injection points are planned to reach the void efficiently and distribute lifting force evenly across the slab. Placement also considers appearance where that matters. **3\. Drilling.** Ports are drilled through the slab, typically around the diameter of a coin. Considerably smaller than the holes mudjacking requires. **4\. Void filling.** Foam is injected under controlled pressure. The first phase fills the void beneath the slab rather than lifting anything. This matters: a slab lifted without the void being filled has nothing supporting it between the injection points. **5\. Lift.** As expansion continues, upward pressure begins to raise the slab. The technician monitors movement continuously, because the objective is a controlled return to grade rather than the maximum achievable height. **6\. Slope check.** Fall is verified before injection stops. Flatwork is usually sloped deliberately to shed water away from a structure, and making a patio dead level when it was intentionally sloped is a failure rather than a success. **7\. Patching.** Injection holes are patched flush with a cementitious material. **8\. Return to use.** Cure time is confirmed for the product used, and in most cases the surface takes traffic the same day. ![Close-up of small drilled injection holes in a concrete patio](/images/content/close-up-of-small-drilled-injection-holes-across-a.webp) ## Why Polyurethane Rather Than Slurry Mudjacking, the older approach, pumps a cementitious slurry through larger holes to achieve the same lift. Both methods work. The practical differences: | | Polyurethane | Mudjacking | | --- | --- | --- | | Port size | Small, coin-sized | Considerably larger | | Added weight on subgrade | Light | Substantial | | Void filling in irregular spaces | Expands to fill | Fills but may leave gaps | | Cure time | Hours or less | Longer | | Surface appearance after patching | Small patches | Larger, more visible patches | The weight point is worth thinking about. The subgrade already proved unable to hold what was on it. Adding significant weight to it is not always the obvious move, which is why polyurethane suits most residential flatwork. ## Control and Its Limits Lift is controlled by managing injection volume and monitoring movement. That control is real but it is not unlimited. **What can be controlled:** the amount of lift, the rate of lift, and which sections rise relative to others. **What cannot be fully predicted:** void volume, which is not measurable until injection begins. This is why a written quote should state the basis for pricing and how a variance is handled, rather than presenting a figure that quietly changes. **What the method cannot do:** restore concrete that has failed. Foam lifts concrete; it does not repair it. > **On the cause, not just the symptom** > > Concrete settles because the material supporting it moved or washed away. Where an active washout is feeding the void, lifting the slab gives you a level surface and a repeat visit. Where we can see a source, we will point it out, and where drainage correction is the real answer we will say so. ## Suitable Applications - Sunken sidewalk and walkway panels, particularly where a lip has become a trip hazard. - Uneven driveway slabs, including approaches and aprons. - Settled patios that have dropped relative to a door threshold. - Pool deck panels that have dropped around the coping. - Concrete steps and landings that have separated from a structure. - Garage slabs that have dropped at the entry. The common requirement across all of them is that the concrete is structurally sound and will lift as a unit rather than as fragments. Quick answers ## Questions About This Topic ### How does foam lift concrete? expand\_more Polyurethane is injected as a liquid through small ports drilled in the slab. It reacts and expands beneath the concrete, first filling the voids that allowed the slab to drop and then, as expansion continues, generating upward pressure that raises the slab. Lift is controlled by managing injection volume and monitoring the slab as it moves. ### How soon can I use the surface? expand\_more Cure is fast. Most residential surfaces are usable within hours of injection and often much sooner. The exact figure depends on the product, ambient temperature, and injected volume, so it is confirmed per product and project rather than quoted as a single number. This is one of the main practical advantages over mudjacking. ### Will the injection holes be visible afterwards? expand\_more The holes are small and are patched flush with a cementitious material. On an aged, weathered driveway the patches will be visible on close inspection because new material does not match old concrete. On a broom-finished surface they blend reasonably well. If appearance is a priority, say so and port placement can be planned accordingly. ## Related Guides ### Concrete Leveling vs. Replacement Compare lifting versus tearing out and repouring concrete: criteria, cost and disruption tradeoffs, longevity, and when replacement wins. Read guide arrow\_forward [Concrete Leveling vs. Replacement →](/guide/concrete-leveling-vs-replacement/) ### Which Concrete Surfaces Can Be Leveled Help judging whether your flatwork is a leveling candidate: suitable surfaces, when leveling isn't viable, trip-hazard remediation, and condition factors. Read guide arrow\_forward [Which Concrete Surfaces Can Be Leveled →](/guide/which-concrete-surfaces-can-be-leveled/) Browse all guides [/guide/ →](/guide/)