Most coating failures on concrete start before the first coat is mixed. A coating can only be as strong as the surface it is bonded to, and a fresh concrete surface is rarely that surface. It is often covered with weak laitance, curing compound, dust, oil or old sealer, and it may be too smooth for a thick system to grip or too rough for a thin one to cover.
Surface preparation is the work that turns that surface into a clean, sound, profiled substrate that matches the coating. This guide explains the concrete surface profile (CSP) scale published by the International Concrete Repair Institute (ICRI), the common preparation methods, how profile relates to coating thickness, and the checks that show a surface is ready. It is general information. The preparation for a real project should be set by a qualified engineer or coatings specialist, using the coating manufacturer’s data sheets and the standards and owner specifications that apply.
Key takeaways
- The ICRI CSP scale runs from CSP 1 (nearly flat) to CSP 10 (very rough) and is defined by a set of physical comparison chips, not by a single number.
- Grinding, shot blasting, scarifying, abrasive blasting, water jetting and scabbling each produce a characteristic range of profiles.
- Thin coatings generally need low CSP values; thick systems and overlays need higher ones. Too rough a profile for a thin film leaves peaks exposed and pinholes.
- Contamination must be removed, not covered. Oil, curing compounds, sealers and laitance prevent bond regardless of profile.
- Pull-off adhesion tests and moisture tests show whether the prepared surface can hold the coating.
What the CSP scale is
ICRI publishes technical guidance on selecting and specifying concrete surface preparation for sealers, coatings, polymer overlays and repair. Part of that guidance is a set of ten molded replicas, known as CSP chips, each showing a different surface texture. CSP 1 looks almost like a smooth troweled floor; CSP 10 looks like concrete with the surface broken out to expose coarse aggregate.
The scale is a visual and tactile reference. On site, the prepared surface is compared with the chips, and the specification states the range that is acceptable, for example “CSP 3 to 5”. There is no simple conversion from a CSP number to a measured depth, although the profile depth generally increases as the CSP number rises. Some specifications add a measured value from a depth gauge or replica putty, but the chips remain the common language between specifier, contractor and inspector.
Because the chips are physical objects, inspectors carry a set and hold them against the surface in several locations. Surfaces are rarely uniform, so it helps to agree in advance how many comparisons are made, where, and what happens at edges, joints and patched areas.
Preparation methods and the profiles they produce
The table shows the range each method typically produces. Results depend on the equipment, the media, the operator, the number of passes and the strength of the concrete, so treat these as general tendencies.
| Method | Typical CSP range | Notes |
|---|---|---|
| Diamond grinding | CSP 1 to 2 | Removes laitance and thin coatings; good for thin films; coarser tooling gives more profile |
| Acid etching | CSP 1 to 3 | Discouraged by many manufacturers; residues, uneven results and no removal of oils or curing compounds |
| Light shot blasting | CSP 2 to 4 | Fast on open slabs; leaves a dust-free surface if recovery works well |
| Medium to heavy shot blasting | CSP 4 to 9 | More passes or larger shot increase profile; can expose aggregate |
| Scarifying (rotary milling cutters) | CSP 4 to 7 | Removes thicker coatings and toppings; leaves grooves that may need filling |
| Abrasive blasting (dry or wet) | CSP 2 to 7 | Works on walls, soffits and irregular shapes; dust or slurry control needed |
| High and ultra-high pressure water jetting | CSP 3 to 10 | Removes weak or contaminated concrete without microcracking; leaves a wet surface |
| Scabbling and needle scaling | CSP 5 to 9 | Aggressive; used before overlays and repairs; can bruise the surface |
| Hydrodemolition and heavy mechanical breaking | CSP 6 to 10 | Concrete removal rather than surface preparation, used in repair |
Bruising and microcracking
Impact methods such as scabbling, heavy scarifying and some breakers can leave a thin layer of microcracked concrete at the surface, often called bruising. A coating or overlay bonded to that layer can fail within the concrete just below the bond line. Specifications often require bruised material to be removed by a following lighter method, such as shot blasting or water jetting, and pull-off tests help reveal it.
Edges, corners and small areas
Large machines cannot reach wall bases, corners, around columns, drains and penetrations. These areas are usually prepared with hand grinders, needle guns or small blast units. They are also where coatings most often start to fail, so they deserve the same inspection as the open field.
Matching profile to coating thickness
The general principle is that the coating must be thick enough to cover the peaks of the profile with the minimum film the system needs, while the profile must be rough enough to give mechanical key and enough surface area for the system’s adhesion. The typical pattern looks like this:
| Coating type | Typical thickness band | Typical CSP range |
|---|---|---|
| Penetrating sealers and very thin films | Up to about 0.1 mm (4 mils) | CSP 1 to 2 |
| Thin film coatings | Roughly 0.1 to 0.25 mm (4 to 10 mils) | CSP 1 to 3 |
| High-build coatings | Roughly 0.25 to 1 mm (10 to 40 mils) | CSP 2 to 4 |
| Self-leveling and broadcast systems, thick membranes | Roughly 1 to 3 mm (40 to 120 mils) | CSP 3 to 5 |
| Polymer overlays | Roughly 3 to 6 mm (1/8 to 1/4 in) | CSP 4 to 6 |
| Cementitious overlays and repair mortars | Thicker than about 6 mm (1/4 in) | CSP 5 to 9 |
These bands are rules of thumb that broadly follow common industry guidance. The coating manufacturer’s data sheet and the project specification set the actual range for a given product. Spray-applied elastomers such as those described in what is polyurea usually have their own primer and profile requirements, and some primers are designed to fill a rough profile before the main coat.
Too smooth or too rough
- Too smooth: poor mechanical key, more risk of delamination, especially under thermal cycling, impact or vapor pressure.
- Too rough for the coating: peaks poke through or are covered by a very thin film, which wears quickly and leaves pinholes. More material is needed to reach the specified minimum thickness, and consumption checks become misleading.
- Uneven: different areas may need different numbers of passes. A single CSP reading taken in the best spot says little about the whole surface.
Contamination: what profile cannot fix
A perfect profile is useless if something is preventing the coating from wetting the concrete. Common contaminants and the usual approaches:
| Contaminant | How it is often found | Usual approach |
|---|---|---|
| Laitance (weak surface paste) | Scratching, pull-off failure in the top layer | Remove mechanically to sound concrete |
| Curing compounds and sealers | Water drops bead instead of soaking in; manufacturer records | Mechanical removal; check after preparation |
| Oil, grease, fuel | Dark stains, water beading, odor | Degrease and remove; deep contamination may need concrete removal |
| Old coatings | Visual; adhesion testing if they are to stay | Remove, or test adhesion and compatibility if overcoating is allowed |
| Efflorescence and salts | White deposits | Remove and investigate the moisture source |
| Dust from preparation | Wiping or tape tests | Vacuum, not sweeping or blowing |
| Biological growth | Visual | Clean, treat as the specification requires and remove residues |
Chemical cleaners alone rarely solve deep contamination. Oils that have soaked into the concrete can move back to the surface after coating, especially when the slab warms. Where contamination is deep, removing the affected concrete and repairing it is often the only reliable option, which is a decision for the engineer.
Soundness and moisture
Is the concrete strong enough?
A coating transfers stress into the top few millimeters of concrete. If that layer is weak, porous or carbonated and friable, the coating will pull it away. Pull-off testing measures the tensile strength of the surface or the bond of a test patch:
- ASTM C1583 is commonly used for the tensile strength of concrete surfaces and the bond of overlays and repair materials.
- ASTM D7234 is commonly used for the pull-off adhesion of coatings on concrete.
The result has two parts: the force at failure and where the failure happened (in the concrete, at the bond line, between coats or in the glue). A specification usually states a minimum value and an acceptable failure mode. Acceptance criteria come from the specification and the manufacturer, not from general guidance.
Is it dry enough?
Moisture in concrete can cause blistering, debonding and poor cure in many coatings. Hydrodemolition and water jetting leave the substrate wet, so drying time must be planned. Common moisture checks include in-situ relative humidity probes (ASTM F2170 describes one method), surface moisture meters and the plastic sheet method in ASTM D4263, which is a qualitative indication rather than a measurement. The coating manufacturer specifies which method and which limit applies; moisture-tolerant primers exist for situations where the limit cannot be met. Our guide to testing concrete moisture explains how these methods work and what to do when a slab fails them.
Outgassing and bugholes
Concrete contains air, and as it warms the air expands and can bubble up through a fresh coating, leaving pinholes. Open bugholes and surface voids on walls make this worse. Typical measures include filling voids with a suitable resurfacer or pore filler, applying primers when the substrate temperature is steady or falling, and following the manufacturer’s advice on primer coats. Our guide to wastewater tank and wet well linings discusses outgassing in damp structures.
Repairs before coating
Preparation often reveals more than expected: delaminated areas, exposed reinforcement, cracks, honeycombing. A coating applied over these defects hides them. Delaminated concrete and corroding steel should be repaired first, using the repair-then-protect sequence explained in concrete spalling prevention. Cracks need a decision on whether they are moving or static, which affects whether a rigid or crack-bridging system is appropriate; our comparison of protective coating systems covers that choice.
Repair mortars also need their own surface preparation and profile, and the manufacturer of the coating should confirm when the repaired areas can be coated, since fresh mortars may still be wet or alkaline enough to affect some coatings.
A practical preparation checklist
- Review the coating data sheet for the required CSP range, cleanliness, moisture limits, temperature limits and primer.
- Survey the surface for contamination, cracks, previous coatings, repairs and damp areas.
- Agree a trial area prepared with the proposed method and checked against the CSP chips, with pull-off tests where specified.
- Prepare the full area, including edges, corners and details, using the method that gave an acceptable trial.
- Inspect profile, soundness, cleanliness and moisture before priming, and record the results.
- Remove dust by vacuum immediately before priming.
- Prime within the window the manufacturer gives, before the surface becomes contaminated again.
The checks in steps 3 and 5 are part of wider coating inspection, covered in coating inspection basics.
Safety and environment
Preparation produces respirable crystalline silica dust, noise, vibration and, with water jetting, high-pressure hazards. Dust extraction, wet methods, respiratory protection and exclusion zones are standard requirements in many countries, and local regulations set the limits. Waste from blasting and water jetting may contain old coatings or contaminants and needs to be collected and disposed of as the rules require.
Frequently asked questions
Is acid etching enough for a floor coating? For most protective coatings, mechanical methods are preferred because acid etching does not remove oils or curing compounds, leaves residues and gives an uneven profile. Some manufacturers still allow it for specific thin products, so check the data sheet.
Can I measure CSP with a gauge instead of the chips? Depth gauges and replica putty give useful numbers, but CSP itself is defined by the chips. If the specification uses CSP, compare with the chips and record any measured values as additional information.
Do new slabs need preparation? Yes. New concrete usually has laitance and often curing compounds, and it may still be too wet to coat. The manufacturer will state a minimum age or moisture condition.
Bottom line
The ICRI CSP scale gives specifiers, contractors and inspectors a shared way to describe concrete surface profile, from the near-flat CSP 1 to the broken-out CSP 10. Choose the preparation method that produces the profile the coating needs, remove contamination and weak concrete rather than covering it, and confirm soundness and moisture with tests before priming. The right CSP range, moisture limits and acceptance criteria for a given system come from qualified engineers, the manufacturer’s data sheets and the applicable standards.