Problem reference / slabs-on-ground
Why is the concrete slab sinking?
A low slab shows movement. It does not, by itself, identify what changed below the concrete or which repair belongs there.
Loss of support
A void or weakened zone below the slab leaves part of the concrete without continuous support.
Fill or base movement
Placed material below the slab may consolidate or move. The original installation record is often unavailable, so the cause still needs field evidence.
Water and drainage
Runoff, leaking utilities, or poorly controlled water can move material or change support conditions. The source and path of the water need to be identified.
Cold-region conditions
Freezing requires water and frost-susceptible soil as well as cold. A seasonal change is evidence to investigate, not proof that frost is the only cause.
Field record
Evidence to gather before discussing a fix.
The goal is to separate what can be observed from what still needs investigation.
- 01
Map the movement
Record the low area, elevation changes, rocking sections, adjacent steps, thresholds, walls, and drainage slope.
- 02
Map the concrete condition
Mark cracks, open joints, spalling, crumbling, prior patches, and unsupported fragments. Leveling does not repair deteriorated concrete.
- 03
Look for a support change
Ask what evidence supports washout, base movement, erosion, leaking utilities, or another loss of support. Keep an unverified explanation labelled as an inference.
- 04
Define the target outcome
State whether the work aims to restore support, improve elevation, correct a trip edge, restore drainage, or prepare for separate work.
- 05
Identify the constraints
Document fixed edges, buried services, connected structural work, finished surfaces, access, and any area that should not move.
Leveling discussion
The slab still has to be a workable unit.
ACI and FHWA guidance put condition assessment before slabjacking. A proposal should explain why the existing slab can be moved, how support will be restored, and which cracks or finish limits will remain.
The underlying water, drainage, or fill condition is a separate scope unless the proposal specifically includes it.
Replacement discussion
The concrete may be the limiting condition.
Severe cracking, deterioration, structural damage, unsuitable geometry, or the need to rebuild the base can make removal and replacement the more relevant discussion.
Replacement still needs a base, drainage, joint, and concrete plan. A new slab does not explain why the earlier one moved.
Building boundary
A basement floor may involve more than a settled slab.
Before treating an interior floor as a routine slab-on-ground repair, determine whether it is connected to footings, walls, utilities, or another structural condition. Movement associated with the building needs the appropriate structural and permit review.
Primary sources / checked September 10, 2026