Concrete Surface Preparation for Coating: CSP Profile and Methods

What surface preparation actually has to achieve

Resin coatings do not bond to concrete in the way most people picture. They bond to the outermost layer of sound cement paste and exposed aggregate, and they draw much of their strength from mechanical keying into an open, irregular surface. That means preparation has two independent jobs: it must take away everything that is not sound concrete, and it must leave behind a surface texture the coating can grip. Neither job substitutes for the other, and a slab can pass one while comprehensively failing the other.

The first thing that has to go is laitance. Laitance is the weak, fine layer of cement fines and water that rises to the surface as fresh concrete bleeds and is worked by the power float or trowel. It looks like concrete, it feels like concrete, and it is chemically the same material — but it is friable, porous and poorly bound to the slab beneath. A coating applied over laitance will bond faithfully to it, and then the laitance will detach from the concrete under load or under vapour pressure, taking the coating with it. The failure looks like a coating problem. It is a preparation problem.

The second category is contamination, and this is where profile alone cannot save a job. Oil and grease that have soaked into the pore structure, curing compounds sprayed on at construction, previous sealers, and above all silicone from adjacent works or old sealant joints are all bond-inhibiting. Opening a coarse profile through a contaminated slab simply gives you a coarse, contaminated slab with more surface area for the contaminant to sit on. Contamination has to be removed or degraded chemically and the residues taken away before mechanical profiling begins, and heavily oil-soaked concrete sometimes has to be cut out entirely. Sparco's TDS puts the requirement plainly: the substrate must be dry, sound, clean and free from oil, grease, loose material and other bond-inhibiting materials.

It is worth stating the consequence explicitly, because it is the single most misunderstood point in this whole subject. Profile and cleanliness are separate acceptance criteria. A slab that has been shot blasted to a textbook CSP 4 and then left overnight collecting dust, or one that was profiled straight through an old curing compound, has not been prepared. It has been roughened.

• Laitance — the weak surface layer of cement fines; must be removed mechanically, not sealed over
• Oil and grease — soaked into the pore structure; profile does not remove it, and heavily contaminated concrete may need cutting out
• Curing compounds and previous sealers — deliberately designed to reduce absorption, so they defeat primer penetration
• Silicone — from sealant joints or adjacent works; migrates, resists most cleaning, and causes localised craters and disbondment
• Dust from the prep itself — the last contaminant added, and the one most often left in place

Concrete Surface Profile: what CSP means and who defines it

Concrete Surface Profile, universally abbreviated to CSP, is the standardised way of describing how rough a prepared concrete surface is. It is defined in ICRI Guideline No. 310.2R-2013, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair, published by the International Concrete Repair Institute. The guideline establishes ten profiles, CSP 1 through CSP 10, running from the barely-textured surface left by light acid etching up to CSP 10, which corresponds to an amplitude greater than 6 mm. Older specifications occasionally cite a shorter range than the current ten profiles; where you encounter one, check it against the current guideline, which runs to CSP 10.

CSP is not measured with an instrument. It is assessed by comparison against a set of moulded rubber or plastic comparator chips, each replicating one profile, which the assessor holds against the prepared slab and matches by eye and by touch. This is a deliberately practical system, and it has the honest limitation that comes with any comparative method: it describes texture, not cleanliness, not strength, and not moisture. A comparator chip cannot tell you the slab is contaminated. Because assessment is comparative, it is worth having the specifier and the applicator agree the target profile on a sample area on site before the main works begin.

The mapping below is the profile-to-system pairing that is commonly specified across the industry, and it is a sound starting point for a specification. It is not, however, a requirement imposed by ICRI Guideline No. 310.2R-2013 — the guideline provides the CSP definitions and guidance on selecting preparation methods, while the profile a particular product actually needs is set by that product's manufacturer and by the project specification. Always read the technical data sheet. As a rule of thumb, the thicker the applied system, the coarser the profile it needs and the more profile it can tolerate without telegraphing texture through to the finished surface.

• CSP 1 through CSP 10 — ten profiles, defined by ICRI Guideline No. 310.2R-2013
• CSP 10 corresponds to an amplitude greater than 6 mm
• Assessed by matching against moulded comparator chips, not by instrument
• The mapping above is commonly specified, not an ICRI requirement — the product TDS governs
• Agree the target profile on a site sample area before the main works begin

Preparation methods compared, and where acid etching stands

Sparco's TDS is specific about the family of methods that is acceptable: concrete must be prepared mechanically, by ball blasting, milling or diamond grinding. That clause is doing more work than it first appears. It is not simply listing three machines — it is excluding chemical preparation from the accepted route, and it is placing the burden on a mechanical process that physically removes material rather than one that dissolves and redeposits it.

Method selection is driven by the profile you need, the amount of material you have to take off, the condition of the existing surface, and the practical constraints of the site — noise, dust, water, headroom, and how quickly the area has to be handed back. In a live Singapore facility working a short shutdown window, the dust containment and the reinstatement time often matter as much as the profile itself. Most real projects use two or three methods together: a primary method across the open field, a secondary method to correct it, and hand tools at the edges.

Acid etching deserves to be addressed directly rather than left as a footnote, because it still appears in specifications and still gets used. The prevailing professional view is that acid etching is inadequate as preparation for resin flooring, and the reasoning is consistent across the industry: it does not remove laitance reliably, because the acid attacks the cement paste indiscriminately rather than selectively lifting the weak layer; it leaves behind salts and reaction products that must be rinsed out completely and rarely are; the rinsing introduces water into the slab immediately before a coating is applied; it does nothing whatsoever to oil, grease, curing compounds or silicone; and it cannot produce a consistent, specifiable profile across a slab of varying density and finish. This is a professional consensus rather than a ruling handed down by a test standard, and it should be understood as such — but it is a consensus, and it aligns with Sparco's own TDS requirement for mechanical preparation.

The preparation sequence, and verifying it before primer goes down

Preparation is a sequence, and the order matters. Contamination is removed before profiling, because profiling through contamination drives it deeper. Profiling happens before defect repair, because you cannot see the full extent of a blowhole or a delamination until the surface is opened — Sparco's TDS requires that weak concrete be removed and that blowholes and voids be fully exposed, which is only possible after the profile is open. Repairs then cure. Verification comes last, immediately before priming, because a slab verified on Friday and primed on Monday has been re-contaminated by three days of site dust.

Dust removal is the step most often done badly. After shot blasting or grinding, the slab carries a layer of fine dust that is, functionally, fresh laitance. It must be vacuumed with industrial equipment, not swept — sweeping redistributes fine dust into the open profile you just spent a day creating and drives it into the pores, where a brush cannot reach it. Vacuum, then check by drawing a clean dark cloth or a gloved hand across the surface. Edges, upstands, coving, and the areas around drains, plinths and column bases cannot be reached by the ride-on machinery and get done with hand grinders and needle guns. These areas are where coatings most commonly lift first, and they are exactly the areas where the temptation to prepare to a lower standard than the main field is strongest.

Verification means checking four things, not one. Profile, against the comparator chips and the specified CSP. Cleanliness, by visual inspection and wipe test — remembering that this is a separate criterion from profile. Moisture, which the coating manufacturer's limit governs (Sparco's TDS caps maximum permissible concrete substrate moisture content at 5%, and the methods for testing it are covered in our article on concrete moisture testing before coating, which is where that subject properly belongs). And the mechanical soundness of the prepared surface, by pull-off testing.

For pull-off adhesion on concrete, the applicable method is ASTM D7234, Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers. One practical detail is routinely missed: where an existing coating is thicker than roughly 20 mils (about 0.5 mm), the coating must be scored through, down to the concrete, around the perimeter of the dolly before the dolly is bonded. Without scoring, the surrounding film shares the load and the test reports a strength the bond does not have. Sparco's TDS sets a minimum pull-off strength of the prepared substrate of 1.5 N/mm² and, for Sparcofloor WBE 400, a minimum concrete compressive strength of 25.0 N/mm². Note that these are the manufacturer's substrate requirements — acceptance criteria for a coated system are set by the project specification, not by the test standard.

Once the slab passes, prime it. Sparco Epoxy Bonding Primer #100 is applied at a coverage of 6–8 m²/kg per coat, with a minimum substrate temperature of 5 °C and curing between +10 °C and +35 °C; Sparco SB Prime 107 is a low-viscosity two-part solvent-based epoxy primer for the same role. Defects, blowholes and voids exposed during preparation are reinstated with Sparco Epoxy Mortar, a non-shrink three-pack steel-trowel-applied repair material, before the primer goes down. Product selection depends on substrate, absorption and exposure and should be confirmed through technical review.

Common mistakes in concrete surface preparation

The failures below are not exotic. They are the ordinary ways that competent people, under time pressure, produce a slab that looks prepared and is not. Coating failures are generally traced back to two dominant mechanisms — inadequate surface preparation and substrate moisture — and sources differ on which of the two leads. What is not in dispute is that both are decided before the first coat is applied, and both are cheap to get right and expensive to correct.

Every item here has the same underlying shape: a step was substituted with something faster that superficially resembles it. Acid instead of a machine. A broom instead of a vacuum. A visual glance instead of a moisture test. Each substitution produces a slab that passes the eye and fails the bond.

• Acid etching instead of mechanical preparation — leaves laitance, salts and moisture behind and cannot produce a consistent profile; Sparco's TDS requires ball blasting, milling or diamond grinding
• Sweeping instead of vacuuming — drives fine dust into the open profile rather than removing it, creating a fresh weak layer at the bond line
• Profiling but not decontaminating — opening a coarse CSP straight through oil, grease, curing compound or silicone; the contaminant is still there, now with more surface area
• Priming a slab that has not been moisture-tested — a slab can be dry at the surface and far above the limit inside; Sparco's TDS caps substrate moisture content at 5%
• Hand-preparing edges, upstands, drains and plinths to a lower standard than the main field — these are precisely the locations where coatings lift first
• Verifying days before priming, then priming over accumulated site dust — verification is only valid immediately before the coat it authorises
• Treating CSP as the whole acceptance test — profile and cleanliness are separate criteria, and a profiled but dusty slab still fails

Checklist: signing off preparation before primer

Use this immediately before the primer is opened, not the day before. Every item is a hold point, and any single failure stops the primer. The value of a written sign-off is that it forces the four acceptance criteria — profile, cleanliness, moisture and soundness — to be recorded separately, so that nobody can pass the slab on the strength of the one that happens to be easiest to see.

Photograph and record the results with the date, time, location and ambient conditions. On a warranty claim or a dispute, the preparation record is generally the first document that gets asked for and the one least often produced.

• Specified CSP confirmed against ICRI comparator chips, checked at multiple locations across the field, not just one
• Sample area agreed with the specifier and applicator before the main works, and the finished field matches it
• All weak and unsound concrete removed; blowholes, voids and delaminations fully exposed
• Contamination removed — no oil, grease, curing compound, previous sealer, silicone or other bond-inhibiting material remaining
• Defects reinstated with a non-shrink repair material such as Sparco Epoxy Mortar, and repairs fully cured
• Slab vacuumed with industrial equipment, not swept; wipe test on a clean cloth comes back clean
• Edges, upstands, coving, drains, plinths and column bases prepared to the same standard as the main field
• Substrate moisture content measured and within the coating manufacturer's limit (Sparco's TDS: maximum 5%)
• Pull-off strength of the prepared substrate verified per ASTM D7234; Sparco's TDS requires a minimum of 1.5 N/mm²
• Where specified, concrete compressive strength confirmed (Sparcofloor WBE 400 TDS: minimum 25.0 N/mm²)
• Substrate and ambient temperatures within the primer's stated range before application begins
• Results photographed and recorded with date, time, location and ambient conditions

Frequently asked questions