Average response time: under 24 hours
Grind the existing floor to a CSP 3-4 profile before any new cementitious or epoxy overlay. Remove all laitance, old coatings, and weak paste with aggressive metal-bond trapezoid discs such as PCD-plus-bar trapezoid tooling where coatings exist, then 30/40 metal shoes. Vacuum, blow compressed air into joints, and apply the overlay manufacturer primer the same day. Skip this step and the overlay delaminates within 12 months - it is the number-one cause of overlay failure.
Old concrete has three layers: a weak dusting surface (laitance), a dense trowel skin, and solid concrete below. Overlays bond to solid concrete, not to the top two layers. Grinding removes both layers and opens a mechanical key. Acid etching, sanding or shot-blasting alone leave inconsistent profiles.
| Overlay type | Thickness | CSP target |
|---|---|---|
| Micro-topping | 2-5 mm | CSP 3 |
| Self-leveling overlay | 5-20 mm | CSP 3-4 |
| Epoxy mortar | 5-30 mm | CSP 4 |
| Heavy-duty resurfacer | > 30 mm | CSP 4-5 |
If the old floor has paint, epoxy or glue, strip it first with PCD tooling. A full-PCD trapezoid disc per head removes coatings fast. Once bare, swap to 30/40 metal-bond shoes to open the concrete. Run a 60/80 pass to remove the 30/40 scratch pattern and give the primer a consistent texture. Do not go finer - overlays need roughness, not smoothness.
For coated floors where old vinyl tile adhesive remains, a 12-small-PCD cup wheel on an angle grinder cleans adhesive from corners and vents that the walk-behind misses.
A: Only if the paint is sound and you grind to CSP 3. If the paint is peeling, strip it completely with PCD first - otherwise the overlay comes off with the paint.
Overlays fill minor dips but cannot bridge 10+ mm. Grind down high spots first, then patch dips, then grind the whole floor.
Yes, the overlay manufacturer supplies one. Grind opens the pores; the bonding agent wets them and creates the chemical link.
A: Yes, and you should. Grind in the morning, prime after lunch, pour the overlay the same day. Overnight dust kills the bond.
Overlay success is decided before the first bag is mixed. Strip coatings with PCD, grind to CSP 3-4 with metal-bond shoes, vacuum and prime same day. JOY TECH supplies PCD and metal-bond tooling for every major grinder brand; tell us your overlay type and old-floor condition for a prep kit.
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.
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