Years ago, the only remedy for uneven sidewalks or foundations was what pros in the business call "rip-and-repour," which means tearing out the old pavement slab and pouring a new one—and spending a lot of time and money doing it.

But nowadays, rip-and-repour has been replaced with a process called "mudjacking"—also sometimes called "slabjacking"—a process that was used for years by highway and heavy industry contractors to level cracked, sunken, uneven pavement. The procedure was messy, the equipment loud and cumbersome, and far too expensive for use on domestic sidewalks, stoops, or slab foundations, but now, with better technology and new equipment, mudjacking is a viable alternative to the old rip-and-repour mantra.

Determine Your Need

During almost any new construction, the sheer weight of a newly poured slab of concrete compacts the subsoil underneath and causes it to "settle" until the subsoil is totally compressed. If the soil settles unevenly, leaving large gaps under the slab, the concrete may begin to tilt or sink into the gap below. If the tilt is acute, the slab may slide under another slab, or even crack.

The need for mudjacking is usually easy to spot. If a section of sidewalk or slab foundation has sunk into the ground—and the section hasn't crumbled or disintegrated too much—a specialist begins by drilling a small hole through the slab. After that, a mudlike substance commonly referred to as "slurry" is pumped through the opening and forced into the void under the sunken concrete, raising it to its original position and keeping it there. The hose is retracted, and the hole is filled in with concrete or asphalt. The slurry then solidifies and stabilizes the subsoil, making further sinking unlikely.

It sounds relatively simple, but the process is a lot more complicated than might appear. "Mudjacking is an art of raising sunken concrete to its original height," explains Tim Murray, the owner of Phillipsburg-based Level Right. "Every slab is different, and there isn't a prescribed method of mudjacking. Some [mudjackers] pump lime, grout, cement mortar, topsoil, or clay. It depends on what the individual mudjacker prefers and has experience with."

Murray stresses that anyone who believes they may have a need for a mudjacker must hire a professional. A skilled mudjacker has to be wary of where utilities, drain pipes, and even sewer pipes are located so none will be filled with the slurry. The ground also has to be evaluated to see if it can stand up to the mudjacking process.

In addition to using mudjacking to level sidewalks and concrete stoops, entire slab foundations can be leveled with the same technique. One mudjacker recalls leveling a floor of a large 60-by-100-foot car dealership mechanic's garage where the floor was so off-kilter, "the red, wheeled cabinets the mechanics were storing their heavy tools in were rolling into the middle of the room." In a matter of hours—with the mudjackers working in the middle of the room and the mechanics fixing cars around them—the floor was leveled.

The Benefits

The first obvious benefit of mudjacking is that without it, the only option a condo owner or homeowner's association has—apart from ignoring the problem—is a "rip-and-repour" of the foundation. "The costs vary depending on the area or thickness of the zone being mudjacked, but mudjacking is always cheaper than breaking out the slab," says Hans Fox, owner/operator of The Presscrete Company in South Plainfield.

If nothing is done with the slab or slabs in question, it can be a huge liability issue. Tom Planert, president of Fairfield-based Concrete Raising of NY/NJ, indicates that a big concern with condominium boards and their owners are the sidewalks; if they aren't level, even a one-inch tripping hazard can spell a hospital stay for an elderly pedestrian—and guess who ends up with the liability.

"We did work for a hospital once where they repoured the entrance two or three times, but it settled each time," said Planert. "The director told me that I wouldn't believe the number of people who were admitted to the hospital for two months for a broken leg, then walk out the front door only to break it again."

In addition to the time and cost saved, mudjacking is far less disruptive to the landscaping. If an area is ripped out and repoured, the grass is usually badly damaged from the heavy equipment and the removal of the old slab. With mudjacking, there's almost no waiting for the concrete to cure. With a rip-and-repour, it takes about a day for the concrete to cure. "They rope the new concrete off and hope some kid doesn't drive his bicycle into it in the meantime," said Planert. "With mudjacking, literally fifteen minutes later, you're able to walk on it."

The nearly instant usage of the affected surface is another factor that makes mudjacking so much more preferable to tearing up the uneven sidewalk or foundation. It's also not nearly as disruptive to tenants. The slurry is mixed in a truck outside the building, dumped into a hopper, and wheeled into a pump. Then the slurry is pumped through a hose down into the slab, so dust is minimal. A condo or apartment owner may end up with a little bit of slurry on the floor of their entry hall, but it's not something that can't be cleaned up with a broom at the end of the day—a far cleaner alternative than the dust storm that is made from a rip-and-repour job.

Another benefit of mudjacking, surprisingly, is that it is more environmentally friendly than repouring concrete. "You shouldn't take good concrete to a landfill that simply doesn't want it," said Planert. "The landfill has enough headaches with garbage and trash, and some guy shows up with chunks of concrete that have no business being there. And, of course, a pavement contractor needs to pay a permit to dump it there, so the mudjacking eliminates all that."

When It's Not For You

Benefits notwithstanding however, mudjacking isn't a universal fix. The procedure is widely used to correct an array of leveling problems in cement, but if the landscape underneath is swampy, mudjacking isn't recommended. When doing an evaluation and estimate, the mudjacker will determine the state of the ground, as well as figure out if there is a sinkhole beneath the slab. If that is the case, mudjacking won't work either.

The most visible example of cases where mudjacking won't fix the problem is when the slab that has settled has broken or disintegrated. In those cases, the mudjacker will recommend a rip-and-repour.

The Price of Stability

The cost of mudjacking depends on the size of the project, but is usually calculated on a square-foot basis, as in the square feet of the slab—or slabs—being lifted. The costs often vary from between $3 and $5 per square-foot. For example, a four-by-four-foot section of sidewalk can cost between $48 and $80 to put back into position, though some variables may apply that can drive up the cost. For example, if the area to be mudjacked is difficult to access—if it's behind a swimming pool, for example—or there is a nice lawn and the owner doesn't want the grass damaged, the price for mudjacking may be $10 to $15 per square-foot, since the specialist now has to figure out how to use the 700-pound pump in a hard-to-reach area. If a lot of slurry needs to be used, the cost can go up as well. But it may still be cheaper than paying up to 50 percent more to have that same area ripped and repoured.

Mudjackers also usually survey the entire area in question, and can work with the building owner or association to budget the project. If the cost is high, an association may be inclined just to do the worst areas right away, and the other, less hazardous areas the following year or year after.

The Guarantee

Most mudjackers will provide a guarantee of their work for at least one year—provided that the ground under the affected area is done settling. One mudjacker indicated that some sidewalks and foundations will settle in increments for seven to 10 years before coming to their final resting point, though most are stable after a year or so. If a section of relatively new sidewalk becomes uneven after a long, wet winter, for example, and the building owner or the association wants to level it in order to avoid liability, most mudjackers will do so—but without offering a guarantee. "If there is any settling, it usually occurs in the first month or two," says Murray. "And if it makes it through the entire season—through all the thawing and rain and sun—the area will probably be fine."

Reducing the Need

There isn't a whole lot that can be done to prevent concrete slabs from settling. The only real way to prevent or reduce the need for mudjacking is to begin before the concrete is even poured. "The soil needs to be compacted before the sidewalk is installed," said Fox. "Once it is put in, there isn't much you can do."

"Usually, the concrete or the pavement is just fine," adds Planert. "It's the underlying soil that's causing the problem when it settles."

Murray concurs, but adds the only other possible way to help prevent the need for mudjacking in sidewalks is to fill the expansion joints—the seams between the individual slabs—if the joints have deteriorated. "If the expansion joint is gone, it means more water running into the crack," says Murray. "It isn't a guarantee, but having them resealed is a good idea."

The Last Word

Depending on the extent of the problem, mudjacking may be a cheaper, cleaner, and quicker way to level a foundation or concrete slab. Doing so also helps prevent accidents—and makes the area look a lot nicer than before. "It's funny when you see mansions and really nice buildings," says Planert. "And the sidewalk looks like someone's broken teeth."

Michael Norris is an independent consultant and freelance writer living in New Hampshire.