Mudjacking / Slabjacking

What Is Mudjacking / Slabjacking?


Also known as concrete raising, concrete leveling, slab lifting, slab raising & concrete lifting. A series of 1-1/4″ holes are drilled through the slabs. Stabilizing grout material is pumped underneath the slab filling the void, pressurizing and hydraulically raising the sunken slab to its original height. Each project varies in accordance to different job site conditions so the consistency of the materials adjust to those variables. Once the slabs are raised, the grout material hardens providing a stable sub-base that won’t erode or settle. Cement is then used to patch the holes.


Proper Application Is Important!


Mudjacking offers you a package of advantages not available with any other method.


For most projects, mudjacking is:



  • faster, cleaner and less costly than replacement

  • readily done at night or other off-hour times

  • completed without requiring access for large equipment (the grout can be pumped several hundred feet)

  • completed without altering the surface texture and appearance


Other valuable advantages of mudjacking:



  • helps provide a stabilizing effect, and a semi-structural bridge support;

  • helps prevent the migration of water beneath the slab, maintaining a moisture content – less affected by freeze-thaw cycles and moisture fluctuations;

  • helps protect adjacent concrete structures from water damage – avoiding foundation settlement/cracking, leaks and basement floor heaves.


Properly executed mudjacking will not create new cracks, but hardly visible existing cracks may tend to open with sagged areas.



In a typical settled slab illustrated here, cracks are wider at “A” and “D” on the top and “B” and “C” on the bottom. On the surface, cracks “A” and “D” (in tension are wide and visible, while cracks “B” and “C” (in compression) are either very fine or not visible at all. Mudjacking will produce a closing force on cracks “A” and “D”, and an opening force on “B” and “C” as the slab is being raised.


Mudjacking is commonly used as the only economical and practical method capable of safely raising large areas of concrete, which may be located alongside full basement foundations. Mudjacking involves a distribution of weight over many injection holes, generally spaced 3 to 4 feet apart. However, spacing is dependent on the strength and thickness of the concrete being raised. Mudjacking does require pressure to raise concrete slabs and does not exert lateral pressure on adjacent foundation walls, beyond the basic physical weight of liquid grout filling the existing void/cavity or the space created as the slab is raised. The grout being pumped into the injections holes is not mechanically confined and is free to escape through any of the adjacent injection holes, through cracks or joints and along the edge of the slab. When any of these things occur, pumping is halted and moved to another hole in order to further distribute the slab’s weight. Movement from one hole to another hole, adding more grout each time, takes place many times until the slab reaches the required height.
NOTE: to ensure a successful project, many binding problems are avoided – by cleaning cracks, chipping or saw cutting – prior to mudjacking.


Rotary percussion drills are usually used, but core drilling can be done in special circumstances.


The exact layout and spacing of injected holes depends on the thickness, condition, and configuration of the slab. Holes are usually placed in a staggered pattern, spaced three to eight feet apart (see diagram below). Concrete with existing cracks or joints require special hole positioning.


After mudjacking is completed, injection holes are patched with concrete so they closely match the original finish and colour.



Grout injection is generally started at the point of greatest settlement. It is usually done about one-quarter inch at a time in any given location. Injection is changed frequently from one point to another, so that no location leads another by more than a quarter inch. To maintain close control and prevent leakage at the slab edges, a stiff grout is generally used for the actual lifting. Only a portion of the holes are used for lifting, while other holes are used for a more flowable grout, filling all remaining cavities, a very important step to the long term success of the project. To monitor the lifting procedure, simple control devices, such as string lines, are stretched across the area being lifted. As the concrete slab comes in contact with the line, lifting is halted.


Poor mudjacking techniques, equipment and materials used, can present a very disappointing project to the customers. Most customers have no way of determining just how complete a job they have received and paid for, until it may be too late. Projects that do not address filling of all void conditions under the slab, will quickly demonstrate excessive crack damage and shifting with little or no control of water seepage conditions. Often unnecessary cracks are created during the raising process as a result of careless rushing, poor hole location and material type, all of which, generally, demonstrate an inexperienced operation.


An alternative technique to mudjacking is foam jacking. This technique utlilizes materials that contain various hazardous chemical and toxic substances, and produce a result that is not as sturdy or long lasting as mudjacking. We do not support this technique.


Read our article on how polyfoam concrete raising is a scam process