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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Surface Preparation
for Coatings: Steel
& Concrete

What surface preparation is, the methods and standards for steel and concrete, how to read a spec, and the checks that decide whether a coating sticks.
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Sa 2½
ISO grade equal to SSPC-SP 10 near-white
ISO 8501-1 / SSPC
CSP 1–10
ICRI concrete surface profile scale
ICRI 310.2R
5°F
Minimum margin above dew point
Industry practice
ASTM F2170
In-situ RH test for concrete slabs
ASTM

Surface preparation is everything you do to a surface before the coating goes on: cleaning it, removing what will not hold a coating, and giving it a texture the coating can grip. It is the least glamorous part of a coating job and the part that decides whether the coating lasts. Coating manufacturers and inspectors agree that poor surface preparation is behind most premature coating failures. This guide covers the methods and standards for steel and concrete, written from the side of the people who make the coatings.

Quick answer

Surface preparation for coating means cleaning a surface and creating the right texture so the coating bonds. On steel, that usually means degreasing (SSPC-SP 1), then abrasive blasting to a specified cleanliness such as near-white metal (SSPC-SP 10 / Sa 2½) with a measured anchor profile. On concrete, it means mechanical prep such as shot blasting or grinding to an ICRI concrete surface profile, repairing defects and testing moisture. In both cases the surface must be clean, dry and above the dew point when coated.

What's in this guide
  1. 1What it does
  2. 2Steel standards
  3. 3Concrete prep
  4. 4Dew point
  5. 5Checklist
  6. 6FAQ
Start here

What surface preparation does

Clean

Remove contaminants

Oil, grease, dirt, salts, old failing coatings, rust, mill scale and laitance all block adhesion.

Profile

Create a texture

A sharp, measured roughness gives the coating mechanical grip and more surface area to bond to.

Condition

Control moisture and temperature

Damp or cold surfaces, or surfaces near the dew point, cause blisters, pinholes and delamination.

Steel

Steel surface preparation standards

Steel prep is specified by cleanliness and profile. The SSPC (now AMPP) and NACE standards line up with the ISO 8501-1 visual grades used outside North America.

SSPC / AMPPNACEISO 8501-1What it meansTypical use
SP 1——Solvent cleaning of oil and greaseAlways first
SP 2 / SP 3—St 2 / St 3Hand and power tool cleaningSpot repairs, mild exposure
SP 7No. 4Sa 1Brush-off blastSweep before recoating sound coatings
SP 6No. 3Sa 2Commercial blastAtmospheric service
SP 10No. 2Sa 2½Near-white metal blastLinings, immersion, most polyurea on steel
SP 5No. 1Sa 3White metal blastSevere immersion
WJ-1 to WJ-4—Wa gradesWaterjetting (no profile created)Removing coatings and salts where a profile already exists
Cleanliness equivalents per SSPC, NACE and ISO 8501-1. Waterjetting cleans but does not create a new anchor profile.
Profile and saltsSpecs usually call for an anchor profile range (often around 2–4 mils for thick coatings) measured with replica tape or a depth gauge per ASTM D4417, and soluble salt testing where chlorides are likely. Follow the coating data sheet.
Concrete

Concrete surface preparation

Concrete must be sound, clean, dry enough and open. Laitance, the weak cement-rich skin on top of a slab, has to come off. The International Concrete Repair Institute (ICRI) uses concrete surface profile (CSP) chips from 1 to 10 to specify roughness.

MethodTypical CSPNotes
Acid etchingCSP 1Not recommended for high-performance coatings; leaves residue and inconsistent profile
Diamond grindingCSP 1–3Good for thin floor coatings; low dust with vacuum
Shot blastingCSP 3–7Fast on floors; most common for polyurea and thick epoxy
Abrasive blastingCSP 3–7Walls, tanks and irregular shapes
Scarifying / millingCSP 5–9Removes thick coatings and uneven concrete
Profile ranges per ICRI Technical Guideline 310.2R. The coating data sheet states the required CSP.

  1. Check the concrete age

    New concrete usually needs to cure before coating; follow the product data sheet.

  2. Test moisture

    Use ASTM F2170 RH probes or ASTM F1869 calcium chloride tests on slabs; ASTM D4263 plastic sheet for a quick check.

  3. Prep mechanically

    Shot blast, grind or abrasive blast to the specified CSP.

  4. Repair

    Fill cracks, bugholes and spalls with compatible repair materials.

  5. Clean and prime

    Vacuum dust, then apply the specified primer to seal outgassing.

Timing

Weather and dew point

Even perfect prep fails if the surface is too cold or damp. Keep the substrate at least 5°F (3°C) above the dew point, check humidity and surface temperature through the job, and coat blasted steel before flash rust forms.

Field noteThe classic failure we see on polyurea over concrete is pinholes and blisters from outgassing when the slab warms up during spraying. Prime first and spray when the concrete temperature is steady or falling.
Before you spray

Surface prep checklist

  • Oil and grease removed (SSPC-SP 1 or detergent wash)
  • Specified cleanliness reached and visually compared to the standard
  • Anchor profile or CSP measured and recorded
  • Soluble salts tested where required
  • Concrete moisture tested and within limits
  • Cracks, pits and defects repaired
  • Substrate temperature at least 5°F above dew point
  • Dust removed and primer applied within the recoat window

For coating-specific guidance see corrosion protection coatings, tank lining and polyurea spray.

Prep and coating

Prep done right, coating that lasts.

A certified ArmorThane applicator handles the blasting, repairs, testing and coating as one job, with the checks documented.

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FAQ

Surface preparation questions

What is surface preparation?

Surface preparation is the cleaning and roughening of a surface before coating so the coating bonds properly. It removes contaminants and weak layers and creates a profile the coating can grip.

What are the main surface preparation methods?

Solvent cleaning, hand and power tool cleaning, abrasive blasting and waterjetting for steel; grinding, shot blasting, abrasive blasting and scarifying for concrete.

What does SSPC-SP 10 mean?

SSPC-SP 10 / NACE No. 2 is near-white metal blast cleaning, equivalent to ISO 8501-1 Sa 2½. It is the usual minimum for linings and immersion service.

Can I acid etch concrete before coating?

Acid etching is not recommended for high-performance coatings such as polyurea and epoxy. Mechanical methods give a consistent, clean profile without residue.

Why is dew point important when coating?

If the surface is at or near the dew point, moisture condenses on it and ruins adhesion. Keep the surface at least 5°F above the dew point.

AT
Written by the ArmorThane technical team. We have manufactured polyurea, polyurethane and polyaspartic coatings, spray foam and plural-component spray equipment in Springfield, Missouri since 1989. Always follow the coating product data sheet and project specification; they override general guidance.

Sources

  1. AMPP (formerly SSPC and NACE) surface preparation standards. ampp.org
  2. ISO 8501-1, visual assessment of surface cleanliness. iso.org
  3. ICRI Technical Guideline 310.2R, concrete surface preparation. icri.org
  4. ASTM D4417, F2170, F1869, D4263 test methods. astm.org

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