What is Slab Jacking ?
Slab jacking, also known as polyurethane injection or poly jacking, is a technique used to lift and level sinking concrete slabs such as garage floors, basement floors, patio slabs, and walkways. It involves injecting a polyurethane material underneath the concrete slab through a network of holes drilled into the slab. The material expands and lifts the slab back into its proper level position.
Why Concrete Slabs Sink
Over time, concrete slabs can settle and sink due to various reasons, such as poor soil compaction before the slab is poured, erosion of soil underneath from water drainage issues, tree roots growing beneath the slab and displacing soil, and freezing and thawing cycles during winter months. This sinking causes the concrete to crack and creates uneven surfaces no longer level. Water can also seep through cracks and accelerate further deterioration from below.
Benefits of Slab Jacking
Slab jacking provides an efficient, cost-effective way to raise and level sunken concrete slabs. Some key benefits include:
It lifts and levels the concrete slab without removing and replacing it. This saves the time and expense of demolition and repouring.
The polyurethane material is injected using minimal equipment through a network of holes drilled into the slab. This minimal disruption limits damage to landscaping.
The material expands and lifts the slab from below in a controlled manner. It can lift slabs that have settled by several inches back to their proper level position.
Once cured, the polyurethane remains flexible, so future cracking or movement is less likely to occur. It also allows the soil to drain properly and prevents further settling.
It provides a permanent solution that lasts 25 years or more, depending on soil and site conditions. The treated areas require no further maintenance.
The process takes just a day or two to complete for an average-sized area like a garage floor, versus weeks for a full replacement.
How Slab Jacking Works
Slab jacking is a multi-step process performed by trained concrete levelling contractors:
1. Site Assessment – The contractor will inspect the site and slab to identify the extent of settling, determine the lift required, and plan the equipment and material needs.
2. Drilling Network—A network of 1-2 inch diameter holes is drilled into the concrete slab on a grid pattern, usually spaced 8-12 inches apart. The holes extend below the slab into the soil base.
3. Injection Port Insertion – Small injection ports are inserted into the drilled holes to funnel the expanding polyurethane.
4. Material Injection – A special polyurethane foam is injected under pressure through the ports using a two-part chemical reaction system. The material expands and fills the void under the slab.
5. Lifting and Leveling – As it cures and expands, the material lifts and levels the slab back into the proper position from below within a couple of hours. The contractor checks for levelness.
6. Sealing – Once lifting is complete, the injection ports are removed, and the holes are sealed for a durable, moisture-proof finish.
7. Inspection—A final inspection checks for any high or low points that need touch-up before the area can be used.
The result is a concrete slab that is once again level and structurally supported, permanently solving sinking and cracking issues. Nearby landscaping, patios, or structures have also been protected during the process with minimal surface disruption.
Choosing a Contractor
When choosing a contractor for slab jacking, look for one with experience completing similar projects. Ask for references from recent jobs they have done. Ensure they are licensed, bonded and have proper insurance. Go with companies dedicated primarily to concrete levelling rather than general contractors. Get detailed written estimates to compare, including lift specifications, materials used, timelines and warranties. An experienced concrete levelling pro can assess the project and provide the best polyurethane injection solution.
When is Slab Jacking Needed?
Slab jacking is typically recommended when a concrete slab has settled or sunk by 1 inch or more. Minor settling under 1 inch can sometimes be corrected using self-levelling concrete compounds poured over the surface. However, a significant 1 inch or more of excellent sinking usually requires polyurethane injection to lift and stabilize the slab from below.
Project Evaluation and Planning
Before providing an estimate, a qualified contractor will thoroughly evaluate the project. This includes inspecting the slab for the extent of settling, measuring elevations, identifying potential obstacles, and checking soil conditions. Based on this, they can determine lift requirements, material quantities, equipment needs, and the best injection pattern. A step-by-step plan is essential for a successful levelling job.
Preparing the Slab Surface
The slab surface may need preparation before drilling. Cracks are often sealed to control where the material is injected from. The surface is cleaned of debris that could clog injection ports. Equipment access routes are identified to avoid tearing up landscaping. Temporary covers protect nearby plants, structures, or utilities from sprayed materials during the process.
Maintaining Polyurethane Quality
For best results, trained crews carefully follow handling procedures for the expanding polyurethane material. It must be stored and mixed correctly with precise temperature controls, as heat causes it to set too quickly, while cold may inhibit expansion. Consistent material quality is essential because under-lift requires a second attempt, whereas over-expansion could crack the slab.
Post-Installation Surface Finishing
Once lifting is complete, injection ports are removed, and holes are sealed with a flexible patching compound. Grinding smooths any remaining burs or ridges flush with the surrounding concrete surface. Final touches like applying an overlay or sealer can improve the appearance and strengthen finished slabs for heavy equipment or vehicle traffic.
Warranties and Preventative Maintenance
Reputable slab jacking companies will provide a written performance warranty, commonly 5-10 years, to guarantee the work. They also offer maintenance advice. Good drainage around the home foundation prevents water from eroding the soil base again. Controlling pest damage from burrowing insects/animals and protecting tree roots reduces future settling potential.
In summary,
Slab jacking using polyurethane injection is an innovative technique for lifting and levelling sunken concrete backers without expensive demolition or replacement. When done by an experienced pro, it provides a long-lasting structural fix that stabilizes the soil surface and prevents further settling issues.
