Preparing concrete for epoxy is not a matter of making the floor look clean. The finished surface must be sound, free of bond-breaking material, dry enough for the selected system, and profiled to that system’s documented requirement. Those conditions have to exist across the field of the floor, at edges, and around repairs.

The short sequence: identify the slab and coating system; inspect and test; remove coatings and contamination; repair appropriate defects; mechanically profile; remove all residue; then verify moisture, cleanliness, soundness, and profile before mixing any coating.

The order can change when testing needs an exposed, prepared surface or when contamination requires specialist remediation. What should not change is the logic: diagnose first, prepare to a written requirement, and verify the result.

Preparation is a specification, not one tool

ICRI describes surface preparation as a combination of removing deteriorated or contaminated concrete, roughening the substrate, and cleaning it to improve the bond of a repair material or coating. Its 310.2R guidance covers different preparation methods, their limitations, benchmark concrete surface profiles, and ways to evaluate the prepared surface.

That framework matters because a thin sealer, a roller-applied epoxy, a broadcast floor, and a troweled overlay do not necessarily need the same surface. Sherwin-Williams’ Form G-1, for example, assigns different profile ranges to different builds within its own flooring portfolio. Those numbers are product-family examples, not a universal specification for epoxy.

Before renting a grinder or buying a primer, obtain the current technical data and installation instructions for the complete coating assembly. Record its requirements for:

  • substrate age and condition;
  • existing coatings and contaminants;
  • moisture test method and acceptance limit;
  • surface preparation method and concrete surface profile (CSP);
  • crack, joint, and patch treatment;
  • substrate and ambient temperature, humidity, and dew point;
  • primer, coat sequence, film build, and recoat windows.

If the documents do not address the actual substrate or exposure, ask the system manufacturer rather than inventing a field modification.

Step 1: assess the slab before disturbing it

Walk the entire area in good light. The inspection should separate cosmetic issues from conditions that can undermine the coating.

Observation Question to resolve before coating
Peeling paint, clear sealer, tile adhesive, or unknown film What is it, how strongly is it bonded, and must it be fully removed?
Dark oil spots or process contamination How deep has the contaminant penetrated, and can clean concrete be reached?
Dusting, laitance, scaling, or weak paste Is the weakness superficial, or is the concrete itself unsuitable?
Cracks, curling, displaced joints, or settlement Is movement active, and does it require engineering or a designed joint detail?
Spalls, pop-outs, and holes Which repair material is compatible with the flooring system and schedule?
Damp areas, efflorescence, leakage, or missing vapor-retarder history Which moisture investigation is needed before selecting the system?
Hard, glossy, power-troweled surface What preparation method will produce the specified profile without leaving weak material?

Sounding, scraping, small test cuts, test patches, or pull-off testing may be appropriate on consequential work. ASTM D7234 covers pull-off adhesion testing for coatings on concrete, while ASTM C1583 is used for concrete surface and repair bond testing. These are controlled test methods, not casual substitutes for a project specification.

Stop and obtain professional evaluation when there is continuing water entry, widespread weak concrete, significant vertical displacement, suspected structural movement, chemical contamination, or uncertainty about a hazardous old coating. A new resin layer cannot restore structural capacity or make an active source of water disappear.

Step 2: identify existing coatings, sealers, and treatments

Concrete may look bare while still carrying a curing compound, penetrating treatment, sealer, densifier, grease film, or fine adhesive residue. A water-drop observation can help locate areas of different absorption, but it does not identify the treatment or certify adhesion.

The safest general assumption is that an unknown film must be investigated and, unless the new system explicitly permits it, removed to sound concrete. Coating over an old layer makes that layer part of the new assembly. Its adhesion, chemical compatibility, cleanliness, and recoat condition all become failure variables.

Test patches can provide useful project evidence when the manufacturer defines how to prepare, cure, and evaluate them. They do not compensate for widespread contamination or a weak substrate.

Step 3: remove oil, grease, and other contamination

Mechanical profiling over an oily floor can spread contamination or drive it into fresh scratches. Remove surface deposits first with a cleaner or degreasing procedure compatible with the substrate and the selected coating manufacturer’s instructions. Collect residues rather than moving them to another part of the slab.

After cleaning, inspect again. Repeated darkening, odor, beading, or poor wetting may indicate deeper contamination. Industrial oils, silicone, tire dressings, food fats, cutting fluids, and previous maintenance products can require different treatment. There is no responsible universal degreaser for every contaminant.

Do not mix incompatible cleaners or improvise chemical treatments. Follow product labels and SDS documents for dilution, ventilation, skin and eye protection, rinsing, collection, and disposal. NIOSH also advises selecting gloves and other protection from the exact resin or chemical information; glove material is not universally interchangeable.

Step 4: treat weak concrete, cracks, joints, and spalls correctly

Remove laitance, dusting paste, loose aggregate, and unsound repairs until the remaining surface is competent. If removal exposes extensive deterioration, pause: continued grinding is not a substitute for determining why the slab is weak.

Defects do not all receive the same filler:

  • Static cracks may be candidates for a compatible rigid or semi-rigid repair detail when the system manufacturer permits it.
  • Active cracks need a detail capable of accommodating expected movement, or they may reflect through the coating.
  • Control joints are intentional crack-control locations; whether and how they are filled depends on movement and service.

Use the dedicated guide to classify cracks, joints, spalls, and movement before repair. It explains why a floor coating is not a structural repair and why movement joints cannot be treated as ordinary static cracks.

  • Expansion and isolation joints are movement joints and generally must remain functional under a designed detail.
  • Spalls and pop-outs require removal of unsound edges and a repair material suited to the depth, traffic, cure schedule, and coating chemistry.
  • Settlement or structural movement is not an ordinary coating-preparation repair.

Repair materials also need their own substrate preparation and cure. Confirm when they may be ground and overcoated. A fast cure label does not establish compatibility with the flooring assembly.

Step 5: make moisture a separate decision gate

Moisture testing is not a final swipe with a handheld meter after every other decision has been made. It can affect system selection, scheduling, primer choice, mitigation design, and whether coating should proceed at all.

Use the test method required by the selected system and project documents. In-situ relative humidity, calcium-chloride moisture vapor emission, and comparative electronic screening answer different questions. Our guide to concrete moisture testing before epoxy explains those distinctions and why Epoxy Science does not publish one universal pass/fail number.

Active leaks, hydrostatic water, failed drainage, plumbing problems, and liquid water entering at walls or joints are not merely a high test result. Find and correct the source before evaluating a coating or mitigation assembly.

Step 6: remove incompatible material and create the required profile

Mechanical preparation is often selected because it can remove weak paste or old material while producing a reproducible texture. Common methods include diamond grinding, shot blasting, scarifying, and abrasive blasting. They are not interchangeable:

Method Typical strengths Important limitations
Diamond grinding Controlled removal, edge access with companion tools, removal of many thin coatings, useful for smaller or irregular areas Tooling must match the coating and concrete; edges need separate work; poor dust control creates serious exposure
Shot blasting Fast, contained preparation of open floor areas and repeatable profiling when correctly set Edge gaps, striping, embedded shot, and excessive aggressiveness are possible; access and power can limit use
Scarifying or milling Aggressive removal of thick material, high spots, and deteriorated surface Can create a much rougher, fractured surface that needs further preparation; not a default method for thin coatings
Abrasive blasting Effective removal and texturing in suitable environments Containment, cleanup, substrate damage, and environmental controls require planning

Grinding concrete for epoxy covers machine and tooling selection, CSP verification, edge work, and silica controls in detail.

Acid etching is not an automatic equivalent to mechanical profiling. It introduces chemical handling, rinsing, residue, drying, and substrate-response variables, and some flooring manufacturers do not accept it for particular systems. Use the acid etching versus grinding comparison only after checking the exact coating instructions and project conditions.

Step 7: clean after profiling

Profiling creates dust and exposes defects. Vacuum using equipment suitable for the dust and task; clean edges, cracks, control joints, penetrations, and low spots, not just the open field. Follow the preparation equipment and coating manufacturer’s cleanup instructions.

Do not use compressed air or dry sweeping as an improvised silica-dust strategy. For concrete grinding, OSHA specifies engineering controls and work practices based on the tool and setting. The goal is to capture dust at generation and avoid redistributing settled material.

If the system permits a final wipe or other cleaning step, use only the documented material and method. A solvent can leave residue, spread contamination, create an exposure, or attack an old layer. “Solvent wipe” is not a universal finishing instruction.

Step 8: verify the surface before coating

Final inspection should be a hold point. Mixing resin before the floor passes inspection turns avoidable defects into a race against pot life.

Verify and document:

  1. Soundness: no loose, scaling, dusty, or weak surface remains.
  2. Cleanliness: the floor, edges, joints, and repairs are free of visible dust, oil, debris, and preparation residue.
  3. Profile: the texture matches the system’s specified method or ICRI CSP comparator range where required.
  4. Moisture: the specified test method was completed at appropriate locations and conditions, and results meet the selected assembly’s limits.
  5. Defects and joints: repairs are cured and prepared; movement joints have an approved detail.
  6. Environment: slab and air conditions are within the product limits, with the required relationship to dew point where specified.
  7. System readiness: the correct primer, components, batch tools, application equipment, and current TDS/SDS documents are on site.

A water-drop or visual check can reveal inconsistency, but neither establishes all seven conditions.

Common preparation mistakes

  • Choosing a grinder before identifying the required coating build and profile.
  • Treating pressure washing as profiling.
  • Grinding over oil and spreading it.
  • Leaving a narrow unprepared band at walls and columns.
  • Filling every joint rigidly without identifying its function.
  • Using a patch that has not cured or is incompatible with the coating.
  • Assuming old paint is a sound substrate because it is difficult to scrape in one spot.
  • Treating a handheld moisture reading as universal acceptance.
  • Selecting primer as a cure for contamination, weak concrete, or active water.
  • Polishing the floor with unsuitable tooling instead of opening it to the required profile.
  • Allowing dust to settle back onto the slab after cleanup.
  • Missing the coating’s application temperature, dew-point, or recoat requirements.

These omissions recur in epoxy floors that peel or delaminate. The visible failure may occur later, but the evidence often begins at the substrate or an interface.

Equipment and product-selection checkpoints

Preparation creates legitimate buying decisions without requiring a product roundup. Select equipment from the condition and specification:

  • Inspection: strong portable lighting, scrapers, straightedges, temperature and humidity instruments, and moisture-testing equipment matched to the accepted method.
  • Removal and profiling: a grinder or other machine sized for the area, compatible diamond or coating-removal tooling, edge tools, shrouds, and suitable dust extraction.
  • Repairs: system-compatible crack or spall materials with a workable cure schedule.
  • Cleaning: task-specific cleaners and collection equipment approved by the coating manufacturer.
  • Application readiness: a compatible epoxy floor primer, mixing equipment, rollers or squeegees, and film-thickness tools when the specified assembly uses them.
  • Protection: controls and PPE selected from the preparation task, exposure assessment, and the current SDS for every chemical component.

The useful commercial question is not “Which tool is best?” It is “Which equipment produces and verifies the required condition on this slab, under these site constraints?”

Preparation checklist

Concrete is ready for epoxy only when the selected system’s written conditions have been met—not when the floor merely looks rough and dry. Preserve inspection notes, photographs, test locations and readings, batch documentation, and product-document revisions. That record supports application decisions and later diagnosis.

This substrate-first approach is the foundation of the broader epoxy flooring system. It also applies to aggregate overlays: the existing pebble-stone outdoor surfacing guide explains why a decorative layer cannot correct an unstable slab or unresolved drainage.

Sources and technical references

Accessed September 2026. Product documents can change; verify the current revision before specifying or installing a system.

  1. Introduction to ICRI Technical Guideline No. 310.2R-2013 — International Concrete Repair Institute
  2. 310.2R-2013: Selecting and Specifying Concrete Surface Preparation — International Concrete Repair Institute
  3. Surface Preparation Guideline Instructions (Form G-1) — Sherwin-Williams High Performance Flooring
  4. Sikagard-62 product information and application instructions — Sika USA
  5. ASTM D4258-23: Standard Practice for Surface Cleaning Concrete for Coating — ASTM International
  6. About epoxies and resins and reproductive health — CDC / NIOSH