Does polyurethane foam work for lifting a house slab?

How foam lifting works under a slab

A crew drills small holes through the slab and injects a two-part urethane mix. The Foundation Performance Association (FPA) describes it this way: the foam "expands creating pressure to raise the slab," and after injection "the lifted area of the slab will sit on the foam"^[1].

The same process is used on driveways and walks. Under a house, it is used in two ways:

1. Alone, to lift or fill under a local low area of the slab.
2. With piers, after the grade beams are jacked and re-supported. FPA says foundation leveling "may also include the injection of grout or foam under the low areas of the slab-on-grade"^[1]. Here the foam fills voids and supports the floor between beams. The piers do the structural work.

Which one you are being sold matters. The second is a support step inside a pier repair. The first asks the foam and the shallow soil to carry the house.

What the foam itself is

Lifting foams are light. One manufacturer lists its slab-lifting foam at 2.75 to 3.25 pounds per cubic foot, "traffic ready in 15 minutes," and certified to NSF/ANSI/CAN 61 for contact with drinking water^[4]. HomeGuide describes polyjacking foam as extremely light, so it "won't stress weak soil," and lists injection holes of 0.50 to 0.63 inches^[3].

Low weight helps on soft fill, where heavy grout could add load. But weight is not the main reason house slabs move on clay. Moisture change is.

What FPA says can go wrong

FPA's repair committee lists these reasons a foam injection repair might fail^[1]:

FPA failure cause	What it means for a house
"If the soil moisture content changes, the slab can move"	Drought or wet seasons can still move the slab
"This is a shallow repair system effected by active moving soil"	The foam sits in the zone that shrinks and swells
Broken sewer or water pipes under the slab	A leak can undo the lift; find leaks first
Trees close to the slab; poor drainage; extreme seasonal moisture change	The same water problems that caused the drop
Improper mixture of chemicals	Off-ratio foam may not perform as designed
Over-injection causing "upward bulging or cracking of the concrete slab"	Too much foam can crack floors and tile
Overly wet foam mix seeping into expansive soil and causing "local heave and out-of-levelness"	A bad mix can make clay swell in one spot
Blowouts from high pressure	Damage at the injection point
Foam entering cracked utility lines "particularly if the foam is pressurized"	It can partly or fully plug a drain line

Notice that the list for mudjacking in the same document is nearly identical^[1]. The material changes. The shallow depth does not.

Myth: "Foam stabilizes the soil, so it is permanent"

Some sales pitches say foam "stabilizes" or "seals" the soil, so the house will not move again. FPA gives no such credit. Its first two failure causes for foam are soil moisture change and active moving soil^[1]. Foam fills the gap under the slab. It does not change how clay under and beyond the foam reacts to wetting and drying. On expansive clay, see expansive clay soil.

Foam also cannot stop heave. If the slab is high in the middle because the edges dropped, or high at one spot because clay swelled, lifting the low parts is not a full answer. See heave vs settlement.

What it costs

Source (date)	Range	Note
Angi (2026)	$5 to $25 per sq ft; slab foundation about $25 per sq ft[2]	Angi, HomeAdvisor and This Old House share one dataset
Angi (2026)	About $3,000 to lift 300 sq ft; most pay $1,500 to $4,500[2]	General flatwork, not house-specific
HomeGuide (Nov 2025)	$8 to $25 per sq ft[3]	Separate dataset
HomeGuide (Nov 2025)	Foam "costs more than concrete but may be better suited to foundation repairs"[5]	No foundation-specific foam price

Prices are national signals as of 2025 and 2026. Interior work through finished floors, the depth of voids and how much foam the job takes all push the price. Ask for the price per pound or per square foot, the estimated quantity, and what happens if more is needed. See polyjacking cost.

Questions to ask before foam goes under your house

• Did an independent engineer recommend foam alone, or foam with piers?
• What caused the low area, and what will be fixed first (leak, gutter, grading)?
• Will a plumbing test be run before and after? See plumbing tests before foundation repair.
• Is the slab post-tensioned, and how will the crew locate the cables before drilling? See post-tension slabs.
• How will lift be monitored so the floor is not over-lifted?
• Does the city require a permit? Houston requires one for foundation repair, which it defines to include stabilizing a structure that has moved^[6].

When to call a pro

• Interior cracks, sticking doors or sloping floors: start with a structural engineer, not a foam quote.
• Signs of a leak under the slab: call a licensed plumber before any lift.
• A slab that was lifted before and dropped again: have an engineer look at drainage, leaks and whether deep support is needed.
• Any contractor who says foam will stop clay from moving: get a second, independent opinion.