Prep Methods for Nonferrous, Wood, Concrete, and Polymeric Substrates

Prep Methods for Nonferrous, Wood, Concrete, and Polymeric Substrates

Quick Answer: CIP Level 2 Domain 5 requires prep methods for nonferrous alloys/metals, wood, concrete, and polymeric materials—not only carbon-steel abrasive-blast grades. Inspectors must know why Sa/SP steel cleanliness standards may not apply, what methods suit each substrate, and special cautions such as aluminum chloride attack and concrete laitance.

Most industrial coating training starts with carbon steel: dry abrasive blast to a defined cleanliness grade and angular profile, then coat. That model fails when the substrate is aluminum, stainless steel, copper alloy, wood, concrete, or a polymer. Applying “SP 10 / Sa 2½ by default” is a common Level 1 habit that Level 2 must correct.

Why Steel Blast Cleanliness Standards Often Do Not Apply

Carbon-steel visual standards (SSPC-SP / NACE / ISO 8501 Sa grades) describe rust, mill scale, and coating residue on ferrous metal. They assume:

• Iron oxides and mill scale are the primary contaminants of concern
• Heavy angular abrasive is acceptable
• A dark or near-white metal appearance after blast is the acceptance cue

Nonferrous metals do not form the same mill scale/rust suite. Over-blasting soft alloys damages dimensions and profile. Iron-containing abrasive or tools can embed ferrous particles that later rust and stain. Polymers and wood can be cut, burned, or melted by aggressive blast. Concrete is assessed by soundness, profile (often CSP), moisture, and contamination—not “white metal.”

Inspection rule: Read the specification and coating PDS for the substrate method. Do not force a steel Sa grade onto aluminum tank walls or epoxy-coated concrete floors unless the document explicitly invokes a comparable standard for that material.

Nonferrous Alloys and Metals

Nonferrous substrates common on CIP jobs include aluminum and aluminum alloys, stainless steels, copper and copper alloys (brass, bronze), zinc (including galvanized surfaces being prepared for paint), titanium, and specialty alloys. Goals of prep are similar—remove soils, oxides, and old coatings that block adhesion—but the tools and media change.

Typical methods for nonferrous metals

Special caution: aluminum and chlorides

Aluminum is vulnerable to chloride contamination. Chlorides promote pitting under coatings and can leave residues that drive underfilm corrosion. Field practices Level 2 inspectors watch for:

• Avoiding chloride-containing cleaners, rinse water of unknown quality, and marine spray left on the surface before coating
• Avoiding copper- or iron-contaminated tools and media that create galvanic sites
• Controlled abrasive selection: iron-free media, clean pots, dedicated hose trains when the specification requires no ferrous contamination
• Recognizing white corrosion products and pitting as conditions that may need more than a wipe-down before coating

Galvanized (zinc) surfaces being painted often use sweep blast, chemical pretreatment, or specialized cleaners rather than full white-metal blast that strips protective zinc.

Stainless steel

Stainless prep emphasizes removing free iron, heat tint, weld scale, and organic soils without destroying the passive film permanently. Methods include non-ferrous tools, appropriate abrasives, pickling gels/pastes or immersion pickling in shop work, and passivation. Embedding carbon-steel grit or grinding with carbon-steel discs can cause rust staining that looks like coating failure later—document tool and media control when the ITP requires it.

Wood Substrates

Wood is organic, anisotropic, and moisture-sensitive. “Blast to Sa 2½” is almost never the correct model.

Prep goals on wood

• Remove dirt, mildew, loose fibers, chalky old finishes, and extractives that bleed
• Open a surface that accepts primer without polishing the grain closed
• Control moisture content within the coating manufacturer’s and specification limits before painting
• Avoid deep gouging that raises fibers excessively or damages edges

Common methods

Inspectors verify dryness (often with a moisture meter when specified), cleanliness, and that primer is applied within the open-time after sanding so dust and raised grain do not recontaminate the surface.

Concrete Substrates

Concrete coating success depends on mechanical and chemical surface condition, not steel cleanliness language.

Laitance — critical concept

Laitance is a weak, cement-rich, powdery layer that forms on the surface of fresh or poorly finished concrete as fine particles and water rise. Coating over laitance produces low adhesion and sheet delamination even when the film looks perfect. Prep must remove laitance until sound, dense concrete is exposed.

Other concrete concerns

• Form-release oils, curing compounds, and sealers that block adhesion
• Contaminants: oils, greases, salts, previous coatings
• Profile appropriate to the system (often described with ICRI CSP chips or equivalent project language)—smooth hard-troweled floors usually need more aggressive prep than broom finishes
• Moisture and vapor emission (tests per specification: plastic sheet, calcium chloride, relative-humidity probes)
• Cracks, bug holes, and unsound concrete requiring repair before coating
• pH and residual cleaners after acid etching if that method is used

Methods used on concrete

CIP Level 2 inspection of concrete prep centers on: laitance gone, specified profile achieved, contaminants removed, moisture acceptable, repairs complete—not matching a steel Sa photo.

Polymeric Substrates

Polymeric materials include plastics, elastomers, fiberglass-reinforced plastic (FRP/GRP), rubber linings being overcoated, and existing organic coatings treated as substrates for maintenance systems. Adhesion is often limited by low surface energy, plasticizers, mold-release agents, and solvent sensitivity.

Typical prep approach

1. Identify the polymer family (PDS and owner data)—solvent that softens one plastic destroys another.
2. Clean with approved cleaners; remove silicone, wax, and mold release thoroughly.
3. Lightly abrade (scuff sand, non-woven pads, or controlled sweep) to degloss without cutting through thin walls.
4. Use chemical etch or adhesion promoters when the manufacturer requires them.
5. Apply primer/tie coat within the open window; dust from sanding must be removed.

Aggressive grit blast can cut FRP gelcoat, heat-soften plastics, or embed media. Waterjetting may remove chalk and loose topcoats but will not create a deep steel-like anchor pattern on a polymer.

Cross-Substrate Comparison Table

Inspector Workflow on Multi-Substrate Jobs

1. Confirm substrate identity on drawings and in the field (mixed-material equipment is common).
2. Locate the specified method and acceptance criteria for that substrate in the job spec and PDS.
3. Verify media, tools, and chemicals will not contaminate the alloy (iron-free on stainless/aluminum when required).
4. Hold points: after cleaning, after profile/abrasion, after rinse/dry, before primer.
5. Document method actually used; if the crew defaults to “blast like steel,” stop and escalate before coating proceeds on the wrong prep standard.

Exam Focus

Expect items that contrast steel blast grades with substrate-specific prep, ask why laitance must be removed on concrete, and test chloride / iron contamination risks on aluminum and stainless. Correct answers reference the substrate and specification—not a universal Sa 2½ rule.