What Holds Up Your Slab After It Is Raised?

The material left under the slab is what carries the load. Traditional mudjacking leaves a variable soil mix, cement slurry leaves a solid cementitious mass at about 780 psi that can bond with the existing base, and polyurethane foam leaves a rigid foam most commonly at 40 to 100 psi.

How is cement slurry different from traditional mudjacking, material by material?

Important Distinction: Cement Slurry vs Traditional Mudjacking

Aspect	Concrete Slab Raising (Cement Slurry)	Traditional Mudjacking
Primary material	Cement-based slurry, custom engineered aggregate blend to improve hardness of cured material.	Soil, topsoil, or “mud” (often low cement)
Final hardened strength	High ~780 psi1	Much lower and highly variable
Consistency and quality control	Engineered and adjustable on site	Variable, less predictable
Long-term durability	High	Lower – more susceptible to erosion/shrinkage
Bond with existing base	Yes	Limited or none

What support does each of the three methods leave under the slab?

Support Characteristic	Traditional Mudjacking	Cement Slurry Raising	Polyurethane Foam
Final material	Soil/mud mix (variable)	Solid cementitious mass, custom engineered aggregate blend to improve hardness of cured material.	Rigid foam
Hardness / Compressive strength	Highly variable5	~780 psi	varies substantially by foam formulation and density most common 40–100psi2
Bond with existing base	Limited or none	Yes	No
Uniformity of support	Often uneven	Can form continuous rigid layer	Can form localized columns or pedestals3
Hole size	1.5-2”	1.5-2”	⅝”
Resistance to pests	Variable	Hardened cement slurry is a mineral material, so it is neither a food source nor a habitat for pests	Polyurethane foam is not a food source for pests, but they can tunnel through such as termites and rodents4
Long-term durability Longevity	Lower	Typically, many years when drainage is corrected	Good when properly installed and drainage is addressed
Cost ranges Chicagoland area	$3-6 /sqft	$3.5-8 /sqft	$5-10 /sqft

Those Chicagoland ranges are for raising the existing concrete. How they sit against tearing the slab out and pouring a new one is worked through in concrete raising vs replacement.

What 100 PSI vs 780 PSI Means

Support Under the Slab: Three Materials Compared

What does that mean for an established home?

For established homes that still have a reasonable base under the slab, the ~780 psi cement slurry creates a harder, more uniform, and more durable support layer that can integrate with the existing base. Traditional mud mixes are weaker and less predictable. Foam provides adequate support but does not form the same solid, bonded layer and pests such as termites and rodents can tunnel through.

Frequently asked questions about support under a raised slab

Does cement slurry bond to the existing base under the slab?

For established homes that still have a reasonable base under the slab, the ~780 psi cement slurry creates a harder, more uniform, and more durable support layer that can integrate with the existing base. Traditional mud mixes are weaker and less predictable. Foam provides adequate support but does not form the same solid, bonded layer and pests such as termites and rodents can tunnel through.

How strong is traditional mudjacking material?

Traditional mudjacking strength is not a single published TDS value. Acme field samples of recovered mud: ~10–20 psi. Practical Foundation Engineering Handbook: typical 2-sack mudjack grout 50–100 psi at 28 days; richer 4-sack mixes ~400 psi. Engineered cement grouts specified by some agencies are higher (e.g., ≥500 psi) and are not the same as soil-based mud.

How strong is polyurethane concrete lifting foam?

Typical concrete-lifting polyurethane foams: 40–100 PSI compressive strength (manufacturer TDS: Alchatek AP Lift, Prime Resins Precision Lift, NCFI TerraThane, HMI, PolyLEVEL)

Can pests get into the material under the slab?

Hardened cement slurry is a mineral material, so it is neither a food source nor a habitat for pests. Polyurethane foam is not a food source for pests, but they can tunnel through such as termites and rodents

What to read next

What each of these materials is made of before it cures, and what the two-part foam chemistry involves on the property, is set out on what goes into the ground under your concrete. The full three-way comparison of cement slurry, polyurethane foam and traditional mudjacking is on the concrete leveling methods comparison.

To have the actual conditions under your concrete assessed, contact SAVE Concrete for a professional evaluation of the driveway, patio, stoop or sidewalk in question.

References on this page

1. Data: Independent lab test data Wisconsin Testing Laboratories

2. Typical concrete-lifting polyurethane foams: 40–100 PSI compressive strength (manufacturer TDS: Alchatek AP Lift, Prime Resins Precision Lift, NCFI TerraThane, HMI, PolyLEVEL)

3. Foam Concrete Leveling: A Detailed Guide to the Pros and Cons lefong.sg/foam-concrete-leveling-a-detailed-guide-to-the-pros-and-cons/ field/contractor observation

4. clemson.edu/public/regulatory/pesticide-regulation/bulletins/bulletin-9-foam-insulation.pdf reported in foam insulation literature (Clemson), not a slab-lift manufacturer TDS.

5. Traditional mudjacking strength is not a single published TDS value. Acme field samples of recovered mud: ~10–20 psi. Practical Foundation Engineering Handbook: typical 2-sack mudjack grout 50–100 psi at 28 days; richer 4-sack mixes ~400 psi. Engineered cement grouts specified by some agencies are higher (e.g., ≥500 psi) and are not the same as soil-based mud.