Quick Answer

Remove old coatings before grinding concrete because a coating clogs diamond discs and prevents the grinding from reaching fresh concrete. Strip paint, epoxy, and mastics with a PCD grinding head or a chemical stripper, scrape off the residue, then grind the exposed concrete with a metal-bond diamond disc. Thick trowelled coatings may need a scarifier or shot-blaster. Always test for lead in old paint and wear appropriate protection.

Why Coatings Must Come Off First

Grinding directly through a coating wastes discs and smears the material across the surface. Paint and epoxy soften with heat, load the diamond bond, and leave a smeared film that prevents the next coat from bonding. Some coatings also contain material that dulls diamonds. The correct sequence is: strip the coating, clean the residue, then grind the concrete. In a pinch a PCD head will remove the coating and some concrete together, but for thick or multiple coats, strip first.

Coating Types and Removal Methods

Thin paint and sealer: a PCD grinding head on an angle grinder or floor machine strips them fast, or a chemical stripper followed by scraping. Epoxy and polyurethane: PCD heads work, and a scarifier is faster for thick trowelled systems; chemical removers work but are slow on thick epoxy. Mastic and glue: tungsten carbide heads are the best, as they shave adhesive off cleanly. Cured urethane coatings may need grinding with a coarse metal bond after a first pass with PCD. Match the method to the coating for the least damage to the slab.

Using Chemical Strippers

Chemical strippers suit small areas, intricate surfaces, and coatings that mechanical removal would damage. Apply the stripper per the label, let it dwell, and scrape the softened coating off with a floor scraper. Neutralise the surface as the label directs, rinse, and let it dry before grinding. Strippers can be caustic and produce fumes, so ventilate the area, wear gloves and eye protection, and dispose of the waste per local rules. Chemical methods are slower than mechanical on large floors, so reserve them for detail work.

Mechanical Removal Technique

For mechanical stripping, work in overlapping passes with a PCD or carbide head, keeping the machine flat and moving. Let the head do the work; pressure creates gouges in the slab. After the coating is removed, switch to a coarse metal-bond diamond disc and grind the exposed concrete to remove the stripping marks and open the pores. Vacuum the residue between passes so the smeared coating does not re-contaminate the surface. Check corners and edges with a handheld grinder, as floor machines miss them.

Safety and Disposal

Old coatings may contain lead, asbestos, or other hazards. Test for lead before dry removal, and check whether the coating is asbestos-containing if the building is older. Wear a respirator rated for the hazard, gloves, eye protection, and coveralls, and work with containment and negative pressure if indoors. Collect the debris and slurry and dispose of it as hazardous or construction waste per local rules. After removal, clean the floor thoroughly before grinding so no residue contaminates the new surface.

For dependable concrete grinding, equip your machine with a diamond trapezoid grinding disc matched to the concrete hardness.

See the diamond grinding cup wheels to keep every stage of the job running with quality consumables.

Once the coating is gone, diamond resin polishing pads help refine the exposed concrete before any new finish goes down.