Building the System, Layer by Layer

Preparation is not a step before the system; it is the first layer of the system, and it constrains everything above it. The two standards that matter:

SSPC-SP6 commercial blast, 2–4 mil angular profile. For new steel and for heavily corroded steel that can be taken down and blasted. This earns the full warranty and the greater-than-500-PSI adhesion figure. Verify profile with replica tape, not by eye, and coat within the same shift before flash rust develops.

SSPC-SP3 power-tool cleaning. For maintenance overcoating where sound, tightly-adhered rust remains and blasting is impractical. Carries a reduced-warranty note. Loose scale and flaking coating must be removed regardless — the test is whether a putty knife can lift it.

Chlorides. Below 7 µg/cm² for coastal, de-icing, and wash-down service. This applies to new steel as much as old; mill handling and outdoor storage deposit salt. Trapped chloride blisters any barrier osmotically, and blisters in a 60-mil membrane are expensive to chase.

Concrete. Profile to CSP 3–5 and test moisture vapor emission before specifying anything over it.

7001 primer is a multi-surface adhesion primer, and in a systems context its real function is normalization: it turns a heterogeneous asset into one predictable surface so a single barrier spec can cover all of it.

Specify 7001 over: galvanized and metallized surfaces, previously painted steel, concrete and masonry, wood and plywood decking, TPO and EPDM membrane, and any substrate where the existing finish may bleed through.

Omit 7001 over: clean, freshly blasted carbon steel coated within the same shift. The polyurea keys directly into the anchor profile and the primer adds cost without adding performance.

The judgement call: aged coatings. Test adhesion on a representative area before committing. If the existing system fails cohesively — that is, it tears within itself rather than releasing from the steel — no primer will save it and the whole coating has to come off.

7001 is quick-setting, which matters on a schedule: on most substrates the barrier layer follows the same day.

Aromatic polyurea chalks and loses gloss under direct UV. Understanding what that does and does not mean is the single most common spec-writing error we see.

What chalking is: surface-level photodegradation producing a dull, powdery finish and colour drift. It is cosmetic. Barrier integrity, tensile strength, elongation, and adhesion are unaffected, and the chalked surface continues to protect the steel underneath.

When to skip the topcoat: plant interiors, roof decks nobody sees, conveyor galleries, tank interiors, undercarriages, equipment bodies where function outweighs finish. Adding an aliphatic topcoat here spends money on appearance nobody will observe.

When to specify it: architecturally exposed steel, customer-facing structures, colour-matched fleet work, and anywhere a facilities group will judge the coating by how it looks in year five. An aliphatic topcoat holds colour and gloss.

A topcoat is not a way to compensate for an under-specified barrier. If the DFT is wrong for the exposure, no top layer fixes it.

When we write one for you, it has these sections — and we would encourage the same structure even if you write it yourself.

• Substrate inventory — every material present on the asset, listed separately
• Surface preparation — SSPC standard, anchor profile, verification method, chloride limit
• Time-to-coat requirement — the clause that keeps blasted steel from flash rusting before it is coated
• Primer — product, where applied, where omitted, and why
• Barrier — product, DFT target and minimum, application method, equipment class
• Topcoat — product and DFT, or an explicit statement that none is required
• Stripe coating — weld toes, edges, fastener heads, and other high-risk detail
• Inspection hold points — profile check, chloride test, wet film readings, final DFT, holiday testing where applicable
• Repair procedure — abrade, 7001, respray; and the six-hour chemical recoat window