Use multiple observations
Note where the sound changes and whether the same area rocks, flexes, settles, cracks, or ponds water. Compare the center, edges, joints, and adjacent panels. Photograph the marked area so a provider can repeat the observation.
- Visible elevation change or panel movement
- Crack pattern and joint condition
- Open edges, erosion, animal burrows, or washed-out soil
- Recent plumbing, utility, irrigation, or drainage work
- Overlay, tile, coating, or bonded finish that may affect sound
Do not assume the void volume from sound alone
A provider may use probing, drilling observations, elevation mapping, or other project-appropriate methods. The proposal should explain what is known, what is assumed, and how material quantity or change orders will be handled if conditions differ.
Connect the finding to a repair objective
The repair objective may be to restore support, raise elevation, fill an accessible space, or replace a failed panel. Those are different jobs. The chosen method should follow the objective and constraints rather than the hollow sound alone.
Questions about does a hollow sound mean there is a void under my concrete?
Can I fill a suspected void with canned spray foam?
Consumer gap-filling products are not a substitute for a project-specific structural lifting or support system. Uncontrolled expansion can create damage or incomplete support.
Does a hollow slab need immediate repair?
Urgency depends on movement, loading, trip risk, nearby structures, utilities, water, and slab condition. Restrict access and seek qualified help when safety is uncertain.
Can a provider price the job without measuring?
A preliminary range may be possible, but a useful final scope should account for the affected area, target, access, material, and uncertainty.
Why this answer is supportable
Reviewed 2026-07-24. Sources explain the general method or decision. They do not diagnose one property, select a provider, or guarantee a result.
Primary answer
A hollow sound can suggest a change in support, thickness, bonding, or subsurface conditions, but it does not prove the size or cause of a void. An inspection should combine sound, elevation, movement, cracks, edges, drainage, and project history before recommending repair.
General decision support only. The cited material does not diagnose subsurface conditions, select a contractor, or guarantee an outcome for one property.Supporting claim
Use multiple observations: Note where the sound changes and whether the same area rocks, flexes, settles, cracks, or ponds water. Compare the center, edges, joints, and adjacent panels. Photograph the marked area so a provider can repeat the observation.
This section summarizes general decision criteria within the cited sources' combined scope. It does not establish the condition, cause, compliance status, or repair fit of one property.Supporting claim
Do not assume the void volume from sound alone: A provider may use probing, drilling observations, elevation mapping, or other project-appropriate methods. The proposal should explain what is known, what is assumed, and how material quantity or change orders will be handled if conditions differ.
This section summarizes general decision criteria within the cited sources' combined scope. It does not establish the condition, cause, compliance status, or repair fit of one property.Supporting claim
Connect the finding to a repair objective: The repair objective may be to restore support, raise elevation, fill an accessible space, or replace a failed panel. Those are different jobs. The chosen method should follow the objective and constraints rather than the hollow sound alone.
This section summarizes general decision criteria within the cited sources' combined scope. It does not establish the condition, cause, compliance status, or repair fit of one property.Review 5 authoritative sources
RAP-11: Slabjacking
American Concrete Institute
Slabjacking is used to level and align slabs-on-ground affected by settlement, erosion, flooding, or shrinkage of supporting soil or base.
Limit: A voluntary field guide, not a diagnosis, design, bid specification, or guarantee for a particular property.Slabjacking (RAP 11) learning objectives
American Concrete Institute University
Appropriate repair selection, hole layouts, settlement mode, grout-pressure monitoring, and verification are core parts of slabjacking practice.
Limit: Summarizes a professional education module; it does not select a method or target for one slab.Web Soil Survey
USDA Natural Resources Conservation Service
Official mapped soil information and interpretations can provide regional and property-area context.
Limit: Mapped soil data cannot reveal exact fill, compaction, leaks, utilities, erosion, or support beneath one slab.Houston IAH climate normals and annual summaries
National Weather Service Houston/Galveston
Houston-area climate normals document substantial annual rainfall and seasonal temperature conditions relevant to regional drainage context.
Limit: IAH station normals are regional context, not Tomball parcel data or proof that weather caused one slab to move.GREAT STUFF Gaps and Cracks Insulating Foam Sealant
DuPont
A common consumer canned foam is marketed to fill, seal, and insulate small household gaps and penetrations.
Limit: Product-specific manufacturer information. It does not support using canned sealant as a structural slab-lifting system.Request a slab assessment
No obligation. The request may be shared with one independent provider only after consent. Provider availability is not guaranteed.
- Surface and exact location of the change
- What moved, how much, and whether it rocks or ponds water
- Known leaks, runoff, roots, utilities, or prior repairs