Both methods raise a sunken concrete slab without tearing it out. They use different materials, and the right choice depends on the slab, the soil and the cause of the settlement.
Slabs sink when the ground beneath them gives way. Common causes include soil that was not compacted well before the pour, erosion from water running under the slab, soil that shrinks or consolidates as moisture changes, backfill settling next to a foundation, and tree roots drawing moisture from the soil. The slab itself is often still in good condition, which is why raising it can make sense.
Both leveling methods work the same basic way. Small holes are drilled through the slab, material is pumped beneath it, the void fills and the pressure lifts the concrete. The holes are then patched. What differs is the material and the equipment.
Mudjacking, also called slabjacking, pumps a slurry through holes in the slab. The mix is typically a blend of soil or sand, water and cement, and sometimes additives such as clay or fly ash. Holes tend to be around 1 to 2 inches across.
It has been used for a long time and is widely available. Because the slurry is heavy, it can add weight to soft soil, and the work is messier and slower than foam, with larger holes to patch.
Polyjacking, also called polyurethane foam injection or foam leveling, injects a two-part polymer that reacts and expands to fill voids and lift the slab. Holes are typically under an inch across, and the foam cures quickly, in as little as about half an hour in some descriptions.
Foam is light, so it adds little load to weak soil, and it can be used on a range of surfaces. The method requires trained technicians, because installation errors can cause problems, and foam can stain nearby surfaces. There are also concerns that some people raise about the material's environmental effects, so ask the installer about the product and its safety data.
The table summarizes the general differences. Individual products and contractors vary.
| Mudjacking | Polyjacking (foam) | |
|---|---|---|
| Material | Cement, soil or sand and water slurry | Two-part expanding polyurethane |
| Hole size | About 1 to 2 inches | Typically under 1 inch |
| Weight added | Heavy | Light |
| Cure time | Slurry needs time to set; slab usable within hours in many cases | Often cures very quickly |
| Cleanup | Messier | Cleaner |
| Limitations | Larger holes, heavier fill, can wash out where erosion continues | Needs trained installers, can stain surroundings, product concerns |
| Cost | Prices vary by area and job | Prices vary by area and job |
Neither method is better for every job. Foam is attractive for soft soils, small access holes and surfaces where a fast return to use matters. Mudjacking is a common choice for large, heavy slabs and where the installer has long experience with the method. Cost, local availability and installer skill often decide the matter.
Whichever method is used, the underlying cause has to be handled. If a downspout dumps water beside the slab or the grade slopes toward it, new voids can form again. Ask the installer to look at drainage, not only the lift. Also ask about a warranty and what it covers, in writing.
A leveling visit typically begins with an assessment: where the slab has dropped, by how much and why. The installer marks injection points, drills the holes, and pumps material while watching the slab rise. Many crews use string lines, levels or lasers to track the lift, and the work is stopped when the surface reaches the planned elevation. The holes are then filled, and the area is cleaned up.
Lift is controlled by the installer, and raising a slab too aggressively can crack it, particularly if it is already weakened. A good installer will tell you if they are not confident the slab can be lifted without damage. They should also explain what happens with adjoining slabs, expansion joints and any attached structures.
Ask whether the quote includes patching the injection holes, how the patch will match the slab and whether any grinding is offered for small edge differences that remain. Ask who handles permits, if any are required, and what the warranty covers and excludes.
Pricing for slab leveling depends on the number and size of slabs, how far each has dropped, access for equipment and local labor costs, so any figure quoted without seeing the job should be treated skeptically. Leveling is usually compared with replacement, and it is often less expensive and less disruptive when the slab is intact, though that is not guaranteed.
Warranties differ widely in length, in what they cover and in whether they transfer to a new owner. Read what is excluded, including drainage or soil conditions that the installer cannot control. A short, clear warranty from an installer who explains it beats a long one full of exclusions.
Ask for references on similar jobs and, if possible, look at a slab that was lifted several years ago to see how it has held.
Raising works best on a slab that is intact. If the concrete is badly broken, if the settlement is severe and ongoing, or if the base has failed across a wide area, replacement may be more sensible. A slab that has been through many freeze-thaw cycles and is scaling may also deserve a new surface. See why concrete cracks for the signs of movement.
Our concrete repair, leveling and sealing page explains how we evaluate a sunken slab, and the sidewalks and steps page covers the walkways where trip hazards are most common.
Foam often allows use soon after injection, sometimes within a short time, and mudjacked slabs are typically usable within hours. Follow your installer's instructions for your job.
It can if the cause, such as erosion or poor drainage, is not fixed. Ask what the installer does about drainage and what the warranty covers.
Ask the installer for the product's safety data and cure information. Practices and products vary, so get specifics before work begins.
Often yes, but attached structures have their own considerations. An experienced installer should look at how the step connects to the house before proposing a method.
Describe the project and the surface you have now, and we will reply with what we need to know.