Mudjacking vs. polyurethane foam lifting for commercial walkways

The short answer

Mudjacking and polyurethane foam lifting are two versions of one repair. In both, a crew drills holes through a settled slab and pumps material underneath until the slab rises to meet its neighbors. Mudjacking pumps a cement-based grout. Foam lifting pumps two liquids that react and expand into a rigid foam.

The foam needs smaller holes, is light, and sets within minutes. On highways, cement grout is given at least three hours. Neither one changes why the slab sank, and both sources that describe the methods say the same thing about that: if the cause is still there, the slab can sink again.

This page compares the two materials. It does not recommend one, and it does not say which a contractor in your city offers.

One repair, several names

The American Concrete Institute's terminology lists mudjacking as another word for slab-jacking, which it defines as raising concrete slabs or filling the voids under them, or both, by injecting a material under pressure. The material can be cement-based or not.

The Federal Highway Administration's 2013 maintenance guide for sidewalks uses the names mud-jacking, concrete raising and slab-jacking for the same thing. So a bid that says "leveling," "raising," "slab jacking," "mudjacking" or "foam lifting" describes one family of repair. The lifting and leveling page explains when that family fits at all.

One related term means something else. Slab stabilization, also called undersealing, fills a void to restore support without raising the slab. If a bid says "void fill," ask whether the slab will also be lifted.

Where the published detail comes from

The most detailed public description of both materials is the Concrete Pavement Preservation Guide, written by the National Concrete Pavement Technology Center at Iowa State University under a Federal Highway Administration agreement. It is a guide for highway pavement. On highways, it says, polyurethane has become the most common material for this work, where cement grout used to be.

A walkway carries people, carts and the occasional service vehicle, not trucks at speed. The hole sizes and waiting times below are that guide's figures for highway work. Most come from its section on slab stabilization, and the guide says the jacking process is similar. Treat them as a description of how the two materials behave, not as a specification for your walkway.

The differences a manager will notice

The material. Mudjacking grout is typically fine aggregate and cement, sometimes with fly ash, mixed with enough water to pump. Polyurethane arrives as two liquids. They combine at the nozzle and expand under the slab into what the guide calls a strong, lightweight, foam-like substance.

The holes. For polyurethane, the highway guide says holes should be no wider than 0.625 inch. For cement grout, it describes drills that cut holes 1.25 to 2 inches across, and injection fittings generally used with 1 inch holes. The sidewalk guide notes that small holes are still visible after mudjacking. On a walkway in front of a storefront or a leasing office, the number and size of the patches is part of the finished look, so ask to see a completed job.

The weight. The highway guide lists light weight first among the advantages of polyurethane, because the material does not add to the load that is settling. It gives a density of about 3 to 4 pounds per cubic foot. Two manufacturers' data sheets opened for this page list cured densities of about 2 to 5 pounds per cubic foot, and one of them lists "lighter weight than mudjacking" as an advantage. The sources opened for this page give no density figure for grout, so this page states none.

The wait. The highway guide gives opening times of 15 to 30 minutes for polyurethane. One manufacturer's data sheet lists 85 percent of full strength at 15 minutes, and notes that results vary with site conditions and temperature. Another sheet says the ground and the air should be above freezing.

For cement grout, the same highway guide says traffic should be kept off the slab for at least 3 hours after grouting, unless a fast-setting material is used, and that the work should not be done below 40 degrees Fahrenheit. Both sets of figures are for road traffic. For a walkway, ask the contractor when people can walk on it and when a vehicle can cross it, and plan the closure around the answer.

The cost. This page gives no prices. The sidewalk guide, written in 2013, says two things about mud-jacking in the same section: that it is "less costly than replacement," and that it is typically "relatively expensive often approaching the cost of sidewalk replacement." Read together, they are a reason to get a replacement price alongside any lifting price. The cost factors guide explains what moves a quote.

The limits both methods share

• Only a settled slab. The sidewalk guide says the method is effective only on sunken sections. A raised panel is a grinding or saw-cutting question, and the sidewalk grinding page explains that grinding fixes a raised edge only on a slab that is otherwise sound. A panel lifted by a tree root is a raised panel too, and the guide to tree roots lifting a sidewalk explains why grinding it is only a temporary fix.
• Only a sound slab. The highway guide says the ideal project for slab jacking, with either material, has settled in one area and is generally free of cracking. A study it reports recommends injecting foam under structurally sound slabs and replacing structurally damaged ones.
• The cause comes first. The sidewalk guide rates the method most suitable where confidence is high that the slab will not sink again, and says to identify and address the cause of settlement before the work. The highway guide adds that when the cause is left alone, the same distress comes back. On a property that cause can be a downspout, a leaking irrigation line or soft fill. The guide to why a sidewalk panel sinks sets out the usual causes and what to ask about each before a lift.
• Drains and utilities. The same guide warns that the reason for a void should be found first, so that material is not pushed into a storm sewer or another utility.
• Lifting takes care. The highway guide says a slab should be raised no more than a quarter inch at a time at any one spot, to avoid stressing it.
• Quantities are hard to predict. The highway guide reports that agencies have had trouble estimating how much foam a job will take, and that results have varied. Ask how a quote handles a void that takes more material than expected.

How long a lift lasts

The sidewalk guide speaks to this for mud-jacking. It lists mud-jacking among the techniques that "will last one to five years," and then says many communities have success with it as a longer term solution. Its durability note says repairs "done appropriately and expertly can be considered permanent fixes," and it shows panels that were mud-jacked more than 20 years earlier and were still in good condition. It also reports that few of the communities it contacted used the method.

That guide does not discuss polyurethane foam. The highway guide reports agency experience with foam under road slabs, with varying results. Its service-life figures are for slab stabilization on highways, such as an estimate of 5 to 10 years on Missouri pavement, and they are not split by material. No source opened for this page gives a service life for foam under a pedestrian walkway, compares the two materials there, or gives a current price.

So a lifespan quoted for either material is the contractor's own claim. Ask what it rests on for your ground.

Questions for a contractor

• Why did this slab sink, and what will stop it from sinking again?
• Which material do you use, and may I see its technical data sheet?
• How many holes, how wide, and how are they finished?
• When can people walk on it, and when can a vehicle cross it?
• What happens if the slab cracks during the lift, or the void takes more material than you estimated?
• What would replacing these panels cost instead?

Next steps

Record each settled panel with the walkway inspection checklist. Where the drop is at a joint, the guide to control and expansion joints explains what the joint was built to do and why sealing it does not fix a panel that has moved. If the walkway has raised edges and cracked panels as well, the three-method comparison sorts them, and replacement covers the broken ones. Once new panels are poured, the new concrete curing guide explains why walking on them and driving across them are separate questions. The glossary defines the terms a bid will use. For a property with many locations, start with assessment planning. Then ask about your project.