Polyurethane Foam Slab Lifting: How Polyjacking Works

Quick answer

Polyurethane foam slab lifting is a repair that raises a sunken concrete slab by drilling small holes through it and injecting a two-part polyurethane that reacts, expands and hardens into a lightweight foam under the slab, filling voids and pushing the slab up.

It lifts and fills; it does not put support under footings or remove the cause of the settlement. One state study found slabs settled a little after lifting. A slab that is part of a house structure should involve an engineer.

Quick facts

The key facts about Polyurethane Foam Slab Lifting, with sources:

Also called: Polyjacking, foam jacking, polyurethane concrete raising ²
Material: Two liquid components that react and expand into a rigid foam ¹
Hole size: About 5/8 inch (16 mm) in the studied method; FHWA says no more than 15 mm for stabilization ¹²
Reopening in highway use: As little as 15 to 30 minutes ²
Lift control: Injection rate, with a string line or laser to watch elevation ¹
Settlement after lifting: Up to about 0.4 inch over two years in one state study ¹
Price: Not quoted here; see the cost drivers section

Key takeaways

Foam lifting injects a two-part polyurethane through small holes; the foam expands under the slab and lifts it ¹.
The foam is lightweight and cures fast, so highway agencies have reopened pavement in as little as 15 to 30 minutes ².
It does not fix the cause. A state study found slabs still settled after lifting, which can open cracks ¹.
Agency results are mixed. Several states reported success, while a Louisiana test saw weaker results on jointed pavement ².
It lifts slabs. It is not underpinning and does not support a footing.

What polyurethane foam lifting is

General information, not a diagnosis of your house. The Federal Highway Administration (FHWA) says polyurethane materials are made of two liquid chemicals that combine to form a strong, lightweight, foam-like substance. After injection under pavement, the reaction expands the material and fills voids ².

An Oregon Department of Transportation (ODOT) report describes the chemistry. One component is a mixture of a polyhydroxy compound, catalysts and water. The other is an isocyanate compound.

They are injected together and react at once to form a rigid foam, with carbon dioxide as a by-product. The foam’s volume is several times that of the liquids, and the expansion lifts the slab ¹.

The method is also called polyjacking or foam jacking. It does the same job as mudjacking, with a different material. It is a slab repair, unlike foundation underpinning, which supports a footing from deeper soil.

Diagram Foam and grout lifting under a sunken slab

Illustrative drawing, not to scale and not a design. It shows foam injected through small holes to fill a void and raise a slab. Hole count, injection order and lift amounts are decided by the installer and, for structural slabs, an engineer.

Foam under a slab is not foam under a footing

Lifting a driveway or patio slab is one repair. Supporting a house foundation that has settled is another. Foam lifting does not replace piers, and an engineer should decide which problem you have before any lifting is done under or near a structure.

How foam lifting works, step by step

ODOT lists the steps for the foam method it studied, and FHWA describes the same process for stabilization and jacking.

Profile. The surface is measured to find where the slab must rise ¹.
Drill small holes. The studied method used holes about 16 mm, or 5/8 inch, through the slab and into the soil ¹. FHWA says the hole diameter for stabilization should not exceed 15 mm ².
Inject. The two components are injected together. They react right away and form a rigid foam that expands ¹.
Control the lift. The amount of rise is set by the rate of injection, and a taut string or laser level monitors elevation. Multiple lifts can be used to reach the profile ¹.
Clean up and seal. Excess foam is cleared from each hole. The hole may be sealed with cement grout ¹.
Reopen. In highway use, traffic can return in as little as 15 to 30 minutes ².

Lifting stresses a slab

FHWA warns that raising a slab too much, or one part more than the next, can induce stress and cracking, and recommends small increments ². Do not try to lift a slab yourself, and do not lift anything attached to a house structure without an engineer.

Foam uses: stabilizing, lifting and sealing voids

The foam uses below are pavement uses documented by highway agencies. House slabs use the same terms and principles.
Use	What it does	Source note
Slab stabilization	Fills voids to restore support without lifting	FHWA lists polyurethane as a common material for stabilization ²
Slab jacking	Lifts a depressed slab back to its neighbors’ level	Done with careful monitoring in small increments ²
Void and water control	Flows into small openings and may reduce water flow through the subgrade	ODOT found foam penetrated openings as small as about a quarter inch ¹
Bridge and slab ends	Used on approach slabs and ramps	ODOT’s case used it on a bridge end panel and adjacent slab ¹

Example: what one state study found after two years

ODOT lifted a bridge end panel and adjacent slab with foam and monitored twelve points for two years. These findings are from that report only and show what to ask, not what to expect on a house slab ¹.

Finding	What the report says	What to ask a contractor
Lift worked	Injected polyurethane can raise concrete slabs to a target profile	What is the target elevation and tolerance?
Settlement after lifting	Slabs settled by up to about 10 mm (0.4 in) after two years, which may open cracks or create new ones	What do you do if the slab settles again?
Strength	Foam strength did not appear to drop after 23 months in air and underground	What is the material’s test record?
Penetration	Foam consistently entered openings as small as 6.4 mm (0.25 in)	How will you handle voids and cracks in the base?
Hole seals	Unsealed holes raveled after two years of traffic; sealed holes showed no damage	How are holes sealed?

Process The chemistry in four steps

Two liquidsPolyol blend and isocyanate
Mix at injectionReaction starts at once
Foam expandsGas makes it rise to several times the volume
Slab liftsFoam fills voids and hardens

Drawn from the chemistry ODOT describes for the method it studied. Source: [1]

The report also warns that its lab density and strength data should not be used as measures of those properties in real field projects, because confinement varies ¹.

Where foam lifting is used, and where it fits less well

FHWA lists polyurethane among common materials for slab stabilization and jacking, and notes agencies such as Oregon, Missouri and Kansas have reported good success using it for stabilization ². Home contractors apply similar methods to driveways, walkways, patios and garage slabs, but the sources here are about highways and bridge slabs.

FHWA also records weaker results in places. In a Louisiana study, foam leveled continuously reinforced and bridge approach slabs well, but results on jointed plain concrete were less positive, since joints kept deflecting under load.

The study’s authors noted that the load transfer devices at that site were not working ². Foam fills voids. It is not a repair for failed joints.

It is also not for slabs that are rising. See expansive clay soil and foundation heave for why a heaving slab is a different problem. And see foundation settlement if a wall or footing is involved.

What foam lifting does well and where it falls short

Strengths in the agency documents

Lightweight, so it adds little settlement load on weak soil ².
Rapid curing, with highway reopening in 15 to 30 minutes ².
Small holes, so patches are small ¹².
Expands to fill surrounding voids and flows into small openings ²¹.
Lift can be built up in successive small lifts ¹.

Limits and trade-offs

Slabs may settle after being raised, which can open or create cracks ¹.
Results varied by agency and slab type ².
One agency reported shortcomings in estimating material quantity before the job ².
Unsealed holes can ravel under traffic ¹.
It lifts slabs but does not support footings or remove the cause of settlement ².

What foam cannot do

FHWA states that if the underlying mechanism behind settlement is not addressed, the same distress will return. Moisture, poor load transfer and poor consolidation are examples ². A foam job under a slab with a leaking pipe or a failing downspout fixes the symptom, not the source.

Foam also cannot repair a broken slab or turn a loose base into a stable one on its own. ODOT’s two-year data showed all twelve monitored points settling slightly after lifting, and the report says the settling may open cracks or create new ones ¹.

It cannot replace deep support. The Foundation Performance Association notes that after a foundation is lifted, a void beneath the slab usually should remain to limit the effects of swelling soil, so filling every void is not always wise ⁴. That is a decision for an engineer.

What drives the price of foam lifting

We do not give prices. A fair figure needs dated local quotes for a defined scope. ODOT noted that the foam contractor priced its job by the weight of material injected, so price can follow the amount of foam, not the size of the slab ¹.

The drivers are slab area and thickness, how far it must rise, void volume, the number of holes, access, weather, patching and cleanup. Any drainage or pipe repair needed to stop the cause adds cost. One state reported shortcomings in estimating material quantities, so ask whether a quote is fixed or by volume ².

Compare foam with grout and with replacement on a like-for-like scope. See the cost guide, the cost calculator and the slab leveling service page.

How to run a foam lifting project

Photograph and date the slab and any cracks. Note gaps at walls and doors. The crack identification tool helps you describe what you see.
Find the water source before the foam goes in.
Ask whether the slab is part of the structure. If it is, ask an engineer first. See the engineer guide.
Get a written scope with the target elevation, hole sealing, cleanup and warranty.
Ask how existing cracks and any settlement after lifting are handled.
Re-measure the slab after the first wet season and keep records.

Keeping a lifted slab level

Make sure downspouts discharge away from the slab. Backfill settles over time, and Kansas State extension advises adding fill to keep soil sloping away at least 6 inches in 10 feet ⁵. See drainage and grading.
Seal the injection holes. ODOT found sealed holes held up better than unsealed holes ¹.
Fix leaking pipes, irrigation and settling backfill promptly.
Re-check level each season with a straightedge and photograph it.
Keep the scope and warranty. See warranties.

Risks to weigh before foam goes under a slab

Cracking from lifting too fast or unevenly ².
Settling after lifting ¹.
Foam lifting a slab that is tied to a wall or footing, which can stress the structure.
Hitting buried lines when drilling.
Treating a moving foundation as a slab problem, which delays the real fix.

When to call a licensed structural engineer

Call one when cracks run through walls as well as slabs, doors and windows stick together with new cracks, a wall or footing is moving, or the slab ties into the foundation. Never drill or inject beside a foundation yourself.

Specifications, permits and who regulates the work

We found no residential code section that specifies foam lifting. The documents we loaded are highway research and guidance: an ODOT report and FHWA’s pavement preservation guide ¹².

State DOTs and cities publish their own specifications, such as one city’s standard for grout slab jacking, which requires documenting the slab’s condition before work and sealing holes flush afterward ³. Those do not apply to private slabs.

Contractor licensing, permits and product approval for home work differ by state and city. Verify a contractor’s license with the issuing board and ask your building department whether a permit applies. A slab that is part of the structure may need engineering review.

Foam is a chemical product, so ask for the product data sheet and the installer’s training. See how we vet for what we check.

Foam lifting next to mudjacking and replacement

Facts from highway agency documents. Neither is ranked here.
Feature	Polyurethane foam	Cement grout (mudjacking)
Material	Two-part polyurethane that expands ¹	Cement-based grout ²
Hole size	About 5/8 inch in the studied method ¹	About 2 to 3 inches in ODOT’s description of conventional grout ¹
Weight	Lightweight ²	Heavier ²
Time to reopen	As little as 15 to 30 minutes in highway use ²	Ask the contractor how long before the slab can take load
Void filling	Expands into surrounding voids ²	Generally near each hole ¹
Results	Good in several states, mixed in others ²	Defined mixes in highway practice ²

Foam lifting myths

Myth Foam lifting is permanent.: Reality ODOT’s slabs settled after lifting, and FHWA warns the distress returns if the cause stays ¹².
Myth Foam always beats grout.: Reality Agency results varied, and the choice depends on the site ².
Myth Foam can fix a sinking house.: Reality It lifts slabs. A settling foundation needs an engineer and often underpinning.
Myth Foam stops water for good.: Reality It can reduce water flow through small openings, but it is not a drainage fix ¹.
Myth Any sunken slab is a foam job.: Reality Broken, rising or structural slabs are different problems.

Soil, water and climate that affect foam lifting

Settlement under slabs often follows fill, drainage faults and water that carries soil away, as in the leaking drainpipe behind ODOT’s case ¹².

In expansive clay regions, slabs can rise and fall with moisture, and a lifted slab can be pushed up again. In freezing climates, frozen or saturated ground affects injection and results. Local conditions decide whether a foam job will hold.

Deciding whether foam lifting fits your slab

Foam lifting fits a mostly intact slab with a localized low spot, where the cause can be found and treated. It fits poorly where the slab is cracked throughout, rising, or tied to a moving foundation.

The guide below turns that into questions. See repair methods and foundation repair for the wider options, and the repair method tool to prepare.

Decision guide If this, then ask that

If One low spot in an otherwise sound slab: Then Ask about the cause of the void and how settlement after lifting is handled ¹
If A leaking pipe or downspout is nearby: Then Fix the water first ²
If The slab is tied to a wall or footing: Then Ask an engineer before lifting
If Joints are working loose: Then Ask whether foam will fix load transfer; the Louisiana study suggests caution ²

Slab contractor or engineer?

If walls, doors or footings show movement, start with an engineer. If only a detached driveway or walk has sunk, a slab specialist may be the right first call. Our engineer or contractor tool helps you decide.

Questions about Polyurethane Foam Slab Lifting

What is polyurethane foam slab lifting?

It is a repair that raises a sunken concrete slab by injecting a two-part polyurethane through small drilled holes. The two liquids react and expand into a lightweight rigid foam that fills voids under the slab and pushes it up. It is also called polyjacking or foam jacking.

How does foam lifting work?

Holes about 5/8 inch wide are drilled through the slab. Two liquid components are injected together, react at once and expand. The expansion fills voids and lifts the slab. Crews control the rise by the injection rate and watch the level with a string line or laser, lifting in steps if needed.

Is foam lifting permanent?

No source promises that. In an Oregon DOT study, slabs settled a little after being raised, up to about 0.4 inch over two years. FHWA says the same distress returns if the underlying cause, such as moisture, is not fixed. Fix the water source and ask about warranty terms.

How is foam lifting different from mudjacking?

Foam uses small holes and a lightweight expanding material. Mudjacking uses larger holes and a heavier cement-based slurry. Highway agencies report good results with foam in several states and mixed results in others. The right choice depends on the slab, soil and cause of settlement.

Can foam lifting fix a sinking foundation?

No. It lifts slabs. It does not carry a footing down to firm soil. If walls, doors or footings are moving, an engineer should evaluate the foundation, and the repair may involve piers instead. Our underpinning page explains the difference.

How fast can a lifted slab be used?

In highway use, FHWA reports traffic can reopen in as little as 15 to 30 minutes after polyurethane injection. A home contractor’s timing may differ, since it depends on the product and the job. Ask for the product’s stated cure time and the contractor’s own instructions.

Can foam lifting crack my slab?

Yes. Lifting too much or too fast can induce stress and cracking, and slabs may settle after lifting, which can open existing cracks or create new ones. Ask how the contractor controls the lift, how holes are sealed and what happens if the slab cracks.

Do I need a permit or an engineer?

Rules vary, and we found no residential code that names foam lifting. If the slab ties into the house structure or walls are moving, involve an engineer. Ask your building department about permits and verify the contractor’s license with the issuing board.

How much does foam lifting cost?

We do not publish prices. The drivers are slab size, lift height, void volume, number of holes, access, patching and any drainage fix. One state study noted the contractor priced by weight of foam injected, so quotes can follow volume. Ask whether your quote is fixed.

Sources

Oregon Department of Transportation, Injected Polyurethane Slab Jacking, FHWA-OR-RD-02-19 (June 2002), retrieved October 14, 2026.
Federal Highway Administration, Concrete Pavement Preservation Guide, 2nd ed., FHWA-HIF-14-014 (September 2014), Chapter 4: Slab Stabilization and Slab Jacking, retrieved October 14, 2026.
City of Regina, Saskatchewan, Standard Construction Specification, Section 2780: Slab Jacking (revised April 2017), retrieved October 14, 2026.
Foundation Performance Association, FPA-SC-08-1: Design, Manufacture, and Installation Guidelines of Precast Concrete Segmented Piles for Foundation Underpinning (2014), design considerations, retrieved October 14, 2026.
Kansas State University Research and Extension, Dry Basements and Crawl Spaces, MF2809 (April 2008), retrieved October 14, 2026.

Expert review

Written by the HyreFoundation Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.

How the numbers were checked: Chemistry, process steps, two-year monitoring results and conclusions come from an Oregon DOT research report on one foam method (the report names the maker; this page does not).

Properties, agency results, hole limits, reopening times and warnings come from the Federal Highway Administration’s concrete pavement guide. Both are about pavements and bridge slabs, not houses, and are used for general mechanics.

The void note comes from a Foundation Performance Association guideline. No residential code section naming foam lifting was found. No prices are given. Rules checked 2026-10-14. General information, not engineering advice.

Suggest a correction. We fix errors and say what changed.