Average response time: under 24 hours
Polishing over a bonded cement topping means finishing a wear layer on an existing structural slab, not the original concrete itself. The topping must bond before grinding, hold enough thickness for traffic, and stay free of hollow spots and interface faults. This guide for the PM and owner representative covers bond-strength proof, thickness limits, hollow detection, the grinding sequence, failure modes and rework clauses.
Figures below are working ranges for bonded leveling or wear toppings over interior slabs. Topping datasheets and the mix design may set stricter bond or thickness limits; record those in the spec before polishing rather than negotiating after delamination appears.
A bonded topping is a cementitious layer of 7 to 50 mm over a prepared slab to level the surface or carry a polished finish. Its strength and wear come from the topping itself, not the parent concrete beneath. Polishing an unbonded or uncured topping transfers grinding forces and traffic to a weak interface, and the finish fails by lifting or dusting, not wear alone. Confirm whether the layer is topping, overlay or parent slab, since acceptance and rework differ.
Before any opening grit, the topping must prove it is bonded to the slab. Pull-off tests are taken at the specified rate, commonly one or two spots per 100 square meters, failing inside the topping rather than at the interface. Typical minimum bond strength is about 1.5 MPa; below that the zone is cut out and rebonded. Record locations, readings and failure mode on the handover record. Visual checks alone cannot show a thin delamination that opens under grinding pressure.
| Condition | Test / sign | Limit or target | Action |
|---|---|---|---|
| Bond strength | Pull-off test | ≥1.5 MPa typical | Below: cut out and rebond |
| Topping thickness | Gauge after screeding | ≥30 mm wear topping | Thin: protect or remove |
| Hollow area | Hammer sounding | No persistent drumming | Local cut-out and patch |
| Surface profile | CSP reference | CSP 3–4 before bond coat | Re-profile if smooth or laitance |
A bonded wear topping should reach at least 30 mm over most of its area to hold polish and resist point load; decorative or leveling toppings may run 15 to 20 mm but carry higher lift risk. Measure thickness after screeding and after opening, marking zones below the minimum. Thin edges around joints and doors curl first, chip under equipment wheels and reflect parent-slab cracking. Where thickness falls short, protect with sealer rather than high-gloss burnishing that exposes the weak layer.
Bond starts at the interface. The slab face must be cleaned of dust, oil and loose material, then profiled to roughly CSP 3–4 so the topping keys in; a smooth or laitance-covered face gives a weak bond line. Bonding agent or slurry coat goes down per the product schedule before placement, without pooling or skinning over. Laitance rising to the topping top should be brushed or ground off before densifier, since a weak top skin seals poorly and powders under traffic.
After cure, sound the whole topping with a hammer or sounding roller in a 1 to 2 m grid, marking any persistent hollow drum rather than a solid ring. Hollow spots are separated or debonded zones that lift under grinding or equipment load. Map them on a floor plan by size and location, separating repairable local hollows from large areas that mean the topping must be redone. A hollow that spreads after the first pass is flagged for re-bond, not touched up with sealer.
Once bond and thickness check out, opening starts with metal-bond diamonds 16, 20, 30 and 40 grit to level the topping and open the paste, then resin pads 100, 200, 400, 800, 1500 and 3000 grit toward the chosen sheen. Keep passes light on thin topping; heavy pressure loosens the bond edge. Densifier goes on after 40 to 100 grit, about 1:64 or 15 ml per liter, worked to full hardness. Cure 7 to 14 days before polishing where allowed, keep RH under 75 to 80 percent, surface temperature 10 to 30 degrees Celsius.
Delamination shows as a lifting sheet or hollow that grows under traffic; curling lifts thin edges around joints and openings. Reflective cracks follow parent-slab joints or cracks through the topping; dusting is a weak top layer that powders under shoes or wheels. Most trace to poor interface prep, insufficient cure, too-thin topping or an early-drying bond coat. Mark the failure type: local lifts are cut out and patched, widespread delamination means remove and replace the topping; reflective cracking is noted in the spec where the parent slab cracks.
Acceptance should require documented bond tests, thickness readings, a sounding map and a walkthrough against the approved sample. Rework clauses state who removes a failed topping, how repairable hollows are patched, and what finish is accepted over thin topping. Record gloss at 2 to 3 m spacing: adjacent bays within 5 units, over 15 rework; inspect under 300 to 500 lux oblique light for scratches. The contract sets the sealer re-coat interval, 3 to 5 years general, 2 to 3 years heavy traffic. Proven before polishing, the topping carries the finish predictably.
Written and reviewed by JOY TECH - an SGS & BV audited, CE/RoHS certified diamond tools manufacturer founded in 2004, exporting to 50+ countries.
Our factory and quality management system are audited by SGS and Bureau Veritas. Products meet CE/RoHS requirements and every piece is 100% inspected before packing.
Verified Certificates
