What Does Controlled Lift Mean in Concrete Leveling?

Controlled lift means the operator can place a small, known amount of material and see the slab move while it is still being pumped. Cement slurry and traditional mudjacking deliver small volumes per trigger pull. Polyurethane foam delivers several times more, and keeps expanding after the trigger is released.

How is material dosed under a slab?

All three methods use a pump with an on/off trigger. The operator presses the trigger to start flow and releases it to stop. The longer the trigger is held, the more material is injected.

Cement slurry and traditional mudjacking deliver relatively small volumes even in a few seconds. The slab begins to move while material is still being pumped, so the operator can see the result in real time and stop when the height is correct.

Polyurethane foam delivers a much larger volume in the same short time. The foam also continues expanding after the trigger is released, so the final lift appears with a delay.

How much material does one trigger pull place?

Calculated Injection Volume for a 1–3 Second Trigger Cycle These are engineering calculations based on assumed equipment output and foam density, not universal field injection rates. Assumptions for foam only: 2 lb/ft³ free-rise density; machine output 10 lb/min (low) to 20 lb/min (high); volumes are expanded foam, not liquid resin. Slurry/mud volumes are typical field pump rates, not the same machines.

Injection time	Cement Slurry	Mudjacking	Foam at 10 lb/min (2 lb/ft³ example)2	Foam at 20 lb/min (2 lb/ft³ example)2, 3
1 second	0.1–0.25 gal	0.1–0.25 gal	≈0.6 gal	≈1.3 gal
2 seconds	0.15–0.5 gal	0.15–0.5 gal	≈1.2 gal	≈2.5 gal
3 seconds	0.2–0.75 gal	0.2–0.75 gal	≈1.9 gal1	≈3.7 gal1

How are the foam volumes calculated?

How the foam numbers are calculated Mass = output × time. Volume = mass ÷ 2 lb/ft³. 1 ft³ = 7.48 gal.

Example, 3 seconds at 20 lb/min: 20 × 3 ÷ 60 = 1.0 lb → 1.0 ÷ 2 = 0.50 ft³ → 0.50 × 7.48 ≈ 3.7 gal. Same shot at 10 lb/min ≈ 1.9 gal.

These are calculated examples, not universal field rates. Actual foam volume also depends on gun, mix chamber, pressure, and formulation.

What does this mean for your driveway or patio?

A short trigger pull with cement slurry places only a small amount of material, and the operator can watch the slab rise and stop at the exact moment it looks right. A short trigger pull with foam places several times more material, and the full effect appears only after the foam expands. This makes very fine adjustments harder and increases the chance of raising a section slightly more than intended (more chance for operator error). Because cement slurry uses smaller, immediately visible doses, it is generally easier to achieve precise, even results on residential slabs.

Five 3-Second Doses: Slurry vs Foam Lift Control

How far does a slab move on one short injection cycle?

Theoretical Lift per Typical Short Injection Cycle⁴

Method	3s Short Cycle	Material Volume	Theoretical Lift on 3×3 ft Slab
Cement Slurry / Mudjacking	Low end dose 3s	≈0.2 gal	≈ 0.036 in (≈ 1/28 in, ≈ 0.9 mm)
Cement Slurry (higher rate) / Mudjacking	high end dose 3s	≈0.75 gal	≈ 0.134 in (≈ 1/8 in, ≈ 3.4 mm
Polyurethane Foam	Low end dose 3s	≈ 1.9 gal	≈ 0.34 in (≈ 5/16 in, ≈ 8.6 mm)
Polyurethane Foam	high end dose 3s	≈ 3.7 gal	≈ 0.66 in (≈ 5/8 in, ≈ 16.7 mm)

Key takeaways Assumptions: no void under the slab; foam volumes are already-expanded in-place foam (not liquid resin); all material stays under a sealed 3×3 ft panel and lifts it as a uniform piston.

Slurry / mudjacking, short 3 s cycle ≈0.20 gal → ~0.04 in ≈0.75 gal → ~0.13 in (about ⅛ in)

Expanded polyurethane foam, short 3 s cycle ≈1.9 gal → ~0.34 in ≈3.7 gal → ~0.66 in (about ⅓–⅔ in)

On those assumptions, one short foam shot lifts the same 3×3 ft area about 5–9× more than one short slurry shot.

That is why a short slurry cycle is the finer increment: each burst adds only a few hundredths to about ⅛ in, so elevation can be nudged in smaller steps. A short foam shot is a larger step on the same panel.

This is a geometric calculation, not a prediction of actual field lift. Soil compression, void geometry, leakage, slab stiffness, reinforcement, and load distribution can substantially change actual movement.

If You Need 1/2 Inch of Lift

Frequently asked questions about dosing and elevation control

Why is a short cement slurry dose easier to control?

That is why a short slurry cycle is the finer increment: each burst adds only a few hundredths to about ⅛ in, so elevation can be nudged in smaller steps. A short foam shot is a larger step on the same panel.

How much more does one foam shot lift than one slurry shot?

On those assumptions, one short foam shot lifts the same 3×3 ft area about 5–9× more than one short slurry shot.

Why is the final foam lift not visible straight away?

Polyurethane foam delivers a much larger volume in the same short time. The foam also continues expanding after the trigger is released, so the final lift appears with a delay.

Are these lift figures a prediction of real field movement?

This is a geometric calculation, not a prediction of actual field lift. Soil compression, void geometry, leakage, slab stiffness, reinforcement, and load distribution can substantially change actual movement.

What to read next

Dose size is one half of control; the pressure behind the dose is the other, and it is set out on how much pressure it takes to lift a concrete slab. 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. Calculation assumptions: 20 lb/min proportioner output and 2 lb/ft³ free-rise foam density. HMI PolyPro 20 equipment information and Graco E-20 specifications are used to establish the equipment-output assumption. Foam density is a separate material assumption.

2. Typical foam injection volume depends on the proportioner, gun, mix chamber, operating pressure, and material formulation. The following values are calculated examples based on specified equipment output and should not be interpreted as universal injection rates.

3. Two separate foam assumptions. Dose volumes (0.6–3.7 gal) use 2 lb/ft³ free-rise foam and 10–20 lb/min output. That is a volume example only. ≈12 psi expansion pressure comes from lab tests at about 4 pcf. Do not use the 2 lb/ft³ gallons to back-calculate 12 psi. Do not use 4 pcf to redo the gallon table.

4. Author calculations