Floor Still Slopes After Mudjacking Decision Tree

Why this matters

Mudjacking (or polyfoam lifting) is a void-fill and lift method for slabs, not a structural repair for a settling foundation. When a floor still slopes after the lift, the common reasons are that the lift target was never set against a survey, the slab is structurally cracked and hinging instead of lifting as a plane, or the underlying soil is still settling and the new grout/foam is riding down with it. Sorting these out matters because re-jacking a slab that sits on still-consolidating soil is a guaranteed callback, and re-jacking a cracked slab can heave one panel and drop the next.

Symptom presentation

A laser or manometer survey shows residual slope after the job, often the same low corner or a new high spot where the lift overshot one zone. The customer reports the floor "still feels off," furniture still rocks, a marble still rolls, or a door re-binds. You may see the slab cracked into independent panels that moved differently, or fresh cracking from the lift itself.

Quick checks

• Run a full elevation survey across the slab and compare to your pre-lift and target survey. Quantify residual slope in inches per foot and map high/low zones.
• Inspect for cracks that divide the slab into separate panels. A cracked slab cannot lift as one plane.
• Check the lift record: was a defined target elevation set, and were injection points spaced to lift the actual low zone?
• Probe or sound for remaining voids: tap test for hollow areas the grout/foam did not reach.
• Look for ongoing soil drivers: plumbing leak under the slab, downspout discharge against it, washout, or fill that is still consolidating.

Isolation tree

1. Did the lift have a measured target, or was it lifted "by feel"?

   • No target means the slope was never corrected to a datum. Branch: re-lift to survey. This is the most common and most fixable cause.

2. Is the slab cracked into independent panels that moved differently during the lift?

   • The slab is hinging, not lifting as a plane. Lifting one panel drops or tilts its neighbor. Branch: structural slab condition.

3. Did the slab lift initially and then drop again over days/weeks?

   • The supporting soil is still settling, or the grout/foam compressed into soft soil. Branch: soil consolidation / bearing.

4. Are there persistent voids that the material never filled (hollow-sounding zones)?

   • Incomplete void fill left unsupported span that re-deflects. Branch: coverage/injection points.

5. Is there an active water source eroding or wetting the subgrade?

   • A leak or surface water is removing or softening support faster than the fill restores it. Branch: water source.

Confirming diagnosis

• No-target lift: The survey simply shows the slope was never brought to a datum. Re-survey, set a target plane, and re-lift. Confirmation is that the geometry, not the material, was the miss.
• Cracked/hinging slab: Crack-map the slab; if independent panels show differential elevation across the cracks, the slab is not monolithic. Lifting individual panels confirms hinging when adjacent panels respond inversely.
• Soil consolidation: A repeat survey over 1-3 weeks showing the lifted zone dropping again confirms the soil, not the lift, is the problem. Probe the subgrade for soft/wet fill; sound material under the grout that still settles points to deep consolidation a surface fill cannot fix.
• Incomplete fill: Tap testing reveals hollow zones; a borescope through a small port confirms an unfilled void.

Remediation

• Re-lift to a measured target plane with adequate injection-point spacing, correcting the slope to within an acceptable tolerance rather than by feel.
• For a cracked/hinging slab, stabilize and where appropriate stitch or replace the slab; lifting a broken slab as if monolithic will not produce a flat floor. Consider full void-fill support under each panel and crack repair before final lift.
• Where the soil is still consolidating or bears poorly, void-fill alone is the wrong tool. Deep support (helical or push piers under the load-bearing edges, or a structural slab pier system) carries the slab to competent strata. Polyfoam can densify shallow fill but cannot stop deep consolidation.
• Eliminate the water driver first: repair under-slab plumbing leaks, regrade and extend downspouts per IRC R401.3, and stop washout before any re-lift.
• Complete the void fill: add injection points to reach the hollow zones, verify with tap test afterward.

Field notes

• The most common miss is lifting by feel instead of to a surveyed datum. Without a target plane set from a laser or manometer survey, the crew lifts until it "looks close," and the residual slope is simply the error of eyeballing. Re-surveying and setting an explicit target plane fixes a large share of these callbacks with no change in method.
• Mudjacking and polyfoam are void-fill and shallow-densification tools, not deep structural support. If the cause is deep consolidation or soft fill running many feet down, the lift rides back down with the soil. A repeat survey over a week or two that shows the lifted zone dropping again is the tell; the answer is deep support, not more grout.
• A cracked slab cannot lift as one plane. Once it has broken into panels, each panel moves independently, and pushing one up tilts or drops its neighbor. Crack-map the slab before quoting a lift; a broken slab needs panel-by-panel support and crack repair, not a monolithic lift.
• Always sound the slab after the job. A tap test that reveals hollow zones means the material never reached part of the void, leaving unsupported span that re-deflects. Add ports and re-fill until the tap test is solid edge to edge.
• Hunt for the water driver before lifting. An under-slab plumbing leak or a downspout dumping against the slab will keep washing out or softening support no matter how well you fill the void. Fix the water first, then lift.

References

• ASTM D1143/D1143M, static axial load testing (used to qualify slab pier support where deep support is added).
• IRC R401.3 and R506, site drainage and concrete-slab-on-ground provisions.
• ACI 302.1R, Guide to Concrete Floor and Slab Construction (flatness/levelness tolerances, FF/FL).
• ICRI 320.2R, Guide for Selecting and Specifying Concrete Repair Materials and Methods.
• FEMA P-2090, foundation/slab performance on consolidating and expansive soils.