Hollow-Sounding Concrete Floors: What Should a Delamination Review Answer?
If part of a concrete floor sounds hollow, ask for a condition assessment before approving a cosmetic treatment. Surface delamination is one possibility, but an informal observation is not a diagnosis. The useful next step is a mapped review that explains what was examined, what remains uncertain, and how the findings affect the proposed work.
Understand what the term describes
The National Ready Mixed Concrete Association describes delamination as separation of a surface layer from the concrete below. In troweled floors, premature or excessive finishing can trap air and bleed water beneath a densified surface. The association also identifies other causes, including reinforcement corrosion and poor bonding between separate placements. A hollow sound can help detect a separation, but it does not by itself establish its cause.
That distinction matters when discussing a garage, shop, or commercial floor. Ask the evaluator to distinguish observations from conclusions. A report saying that an area sounded different should not be treated as equivalent to a report establishing the affected depth, extent, and appropriate repair.
Request a map, not just a verbal description
Before the visit, sketch the room and label doors, columns, equipment, and the locations that prompted concern. Photograph visible changes and note when they first appeared. Include previous patches, toppings, or coatings in the history if you know about them. Do not chip away the surface merely to produce a more convincing photograph.
Ask for a marked plan showing the areas reviewed and the limits of access. A floor partly hidden beneath shelving is not the same inspection assignment as an empty room. Have the evaluator identify which locations were accessible, which were excluded, and whether the remaining areas need a return visit.
NRMCA lists sounding methods and more specialized detection techniques. Let the qualified evaluator select the method and explain its limitations. Your deliverable should connect each finding to a location, not leave you trying to remember which patch someone pointed toward during a walkthrough.
Separate the investigation decision from the repair decision
If more investigation is recommended, request its purpose in writing. What uncertainty will it address? Who will interpret the result? Will the work leave openings or disturbed finishes, and who will restore them? Agree on access and authorization before the investigation begins, especially where several tenants or vendors share the floor.
For the repair proposal, ask how the contractor established the proposed boundaries. Request a distinction between confirmed work and an allowance for conditions discovered later. Identify who can approve an expanded area and what record will accompany that approval. This is more useful than accepting an undefined promise to repair all bad concrete.
NRMCA describes repairs that remove the separated layer and prepare the underlying concrete; extensive conditions may call for broader resurfacing. Ask how the recommended approach follows the actual findings. Do not choose between patching and a wider repair solely from the appearance of the floor.
Write down the floor-use handoff
Tell the contractor what happens in each affected area: storage, customer access, equipment movement, or a planned finish installation. Request written instructions for temporary access restrictions and eventual reopening. Name the person responsible for relaying those instructions to occupants, cleaners, and any flooring vendor.
Before approving the work, ask what the completed repair is expected to look like and how acceptance will be documented. Keep appearance expectations separate from the condition findings. A proposal should explain any remaining investigation or follow-up rather than allowing a newly uniform appearance to become the entire closeout record.
For a Middle Tennessee property, start the conversation with the address, floor use, photographs, and any available repair history. Milliken Corporation lists concrete floor slabs and repairs among its services. Ask the team to confirm the appropriate scope and whether the evaluation needs a separate specialist; do not assume a particular testing service is included.
Frequently asked questions
Should I approve a coating while the hollow areas are still unexplained?
Ask the evaluator and coating contractor to resolve the open condition questions first. Request a written explanation of what preparation or repair is included, and keep the coating decision linked to that agreed scope.
Does a hollow sound mean the whole floor must be replaced?
Do not authorize whole-floor replacement from that observation alone. Ask for the mapped findings and an explanation of why the recommended repair boundaries are appropriate before choosing the scope.
What should I keep after the review?
Keep the dated condition map, photographs, assessment findings, access exclusions, approved repair scope, and any follow-up instructions together. These records give future contractors a clearer starting point than an invoice with only a room name.