Slab Jacking vs Polyurethane Leveling

Why this matters

A homeowner with a sunken driveway, sidewalk, or patio has two main options to fix it: traditional mudjacking (pump cement slurry under the slab) or polyurethane foam leveling (inject expanding polyurethane foam). Both methods lift the slab to original position. The price difference is significant (a moderate for typical mudjacking vs a significant for polyurethane); the customer often doesn't understand why polyurethane costs more. The right choice depends on the slab's condition, soil conditions, customer's expectations, and the contractor's equipment. Knowing the trade-offs allows you to quote the right method and explain the value.

The two methods

Mudjacking (slab jacking)

Pump a cement-based slurry (typically Portland cement, sand, water, sometimes a soil component) through holes drilled in the slab. The slurry fills voids under the slab and lifts the slab back to its original position.

Polyurethane foam leveling

Inject expanding polyurethane foam through holes drilled in the slab. The foam expands within seconds, lifting the slab.

When to recommend each

Recommend mudjacking when

• Cost is the dominant concern
• Slab is supporting low loads (sidewalk, patio)
• Customer has time for cure time
• Soil conditions are stable

Recommend polyurethane when

• Cost is less of an issue
• Slab is supporting significant loads (driveway, commercial)
• Customer wants immediate use after repair
• Soil conditions are marginal (foam handles voids better)
• Aesthetic matters (smaller holes are less visible after patching)
• Repeat settlement is a concern (foam is lighter, less likely to re-settle)

Recommend neither (refer or full replacement)

• Slab is severely cracked
• Slab is sinking due to underground water issues that need addressing first
• Slab is sinking due to expansive clay that will keep moving
• Slab is too deep to lift (over 4 to 6 inches)

Procedure for typical slab leveling

Step 1: Assess the situation

Walk the slab:

• Measure how much the slab has settled (use level on adjacent slabs)
• Identify the cause if possible (water erosion, settling soil, expansive clay)
• Verify the slab is sound (not cracked badly)
• Note utilities under the slab (if any)

Step 2: Choose the method

Based on the considerations above and the customer's preferences.

Step 3: Mark and drill holes

For mudjacking:

• Mark holes at intervals (typically 2 to 4 ft apart)
• Drill 1.5 to 2 inch holes
• Continue across the slab

For polyurethane:

• Mark holes at intervals (typically 2 to 4 ft apart)
• Drill 5/8 inch holes
• Continue across the slab

Step 4: Inject and lift

For mudjacking:

• Pump cement slurry through holes
• Slurry fills voids and lifts the slab
• Monitor slab elevation during injection
• Adjust pressure to control lift

For polyurethane:

• Inject foam through holes
• Foam expands rapidly (within seconds)
• Slab lifts as foam expands
• Multiple injection points coordinate the lift

Step 5: Verify alignment

• Check slab elevation with level or laser
• Slab should match adjacent unsettled slabs
• Lift slowly; over-lift is hard to correct

Step 6: Patch holes

For mudjacking:

• Plug holes with cement patch
• Allow to cure (typically 24 hours)

For polyurethane:

• Plug holes with concrete patch or cement
• Foam itself plugs much of the hole

Step 7: Customer instructions

• Mudjacking: wait 1 to 3 days before normal use
• Polyurethane: wait 30 minutes before normal use

Settlement causes that complicate repair

Soil washing

Water from a downspout, broken pipe, or grading issue washes soil from under the slab. The slab settles. Fix the water source before lifting:

• Redirect downspouts
• Fix grading
• Repair broken pipes

Without addressing the water source, the slab will re-settle.

Expansive clay

Clay soil that expands when wet, contracts when dry. The slab moves seasonally. Leveling lasts until the next major weather change. Customer should be aware:

• Re-leveling may be needed periodically
• Drainage improvement helps
• French drains can address the issue

Settling from inadequate compaction

When the slab was poured, the soil underneath wasn't properly compacted. Settlement continues until the soil fully compacts.

• Leveling addresses current settlement
• Continued settlement may occur
• Customer should monitor

Tree root removal / death

A large tree was removed; roots were left to decay. As roots decay, the soil settles.

• One-time settlement; should stabilize after the roots fully decay (5 to 10 years)
• Leveling fixes current issue

Limitations of both methods

Lifting limits

• Standard limit: 4 to 6 inches of lift
• Beyond that, the slab structurally compromised
• Settled too far = replacement is the only option

Cracked slab

• Severely cracked slabs may break during lifting
• Inspect carefully before quoting

Reinforced slab

• Slabs with rebar lift better than unreinforced
• Old slabs without rebar are more fragile

Slabs over utilities

• Lifting may damage utilities below
• Coordinate; sometimes manual jacks vs hydraulic foam

Adjacent structure

• Slab attached to foundation: cannot lift without affecting the foundation
• Specific situations require engineering review

Material lifecycle

Mudjacking slurry

• Cement-based; cures permanently
• Behaves similar to concrete
• May develop hairline cracks over decades
• Doesn't dissolve or wash away

Polyurethane foam

• Closed-cell rigid foam
• Doesn't compress over time
• Doesn't absorb water (waterproof)
• Stable for decades
• Some products advertised as "lifetime"

Customer education

For each customer:

• Explain both methods
• Provide cost comparison
• Identify the root cause of settlement (so customer knows)
• Address the root cause if practical
• Set expectations (current fix; potential future settling)

Brand options

For mudjacking:

• Often local contractor's own slurry mix
• Some brand-specific products available

For polyurethane:

References

• ACI (American Concrete Institute) standards.
• ASTM C476 (Concrete Slabs).
• Manufacturer literature: PolyLevel, URETEK, HMI, PolyJacking.
• Manuall internal: Foundation Repair Foundation Settling Diagnostics.