The Real Cost of the Wrong Coating on Exposed Steel

Exposed steel is a design feature and a liability, and the wrong coating system turns it into an unplanned repaint.

For architects, engineers and owners, exposed architectural steel is one of the most visible decisions on a building, and the coating decides how long it stays that way. The wrong system rarely fails on day one. It fails slowly and in public, and the bill arrives as an early repaint that nobody budgeted for.

This article covers how the wrong coating shows up on exposed steel, where the cost lands, and which specification decisions prevent it.

What Is the Real Cost of a Coating Failure on Exposed Steel?

The real cost is the unplanned repaint, not the paint. Material is a small share of what an owner pays over the life of exposed steel, while access, preparation in place and disruption make up most of a repaint.

On projects of this type, the coating was often selected late, by the fabricator or through a substitution. No one confirmed that the primer, the finish and the exposure belonged together.

Failure Modes: How the Wrong System Shows Up

Exposed steel is a design feature, so the first sign of trouble is usually cosmetic. That makes it easy to dismiss until it spreads.

The common failure modes on architectural steel are:

• Fading and Chalking: Finishes not built for ultraviolet exposure lose color and gloss outdoors, and an epoxy left as the exterior finish coat chalks long before the steel is at risk.
• Rust Bleed at Edges and Connections: Corrosion starts where the film is thinnest or the preparation weakest, at sharp edges, welds, bolted connections and crevices, and the staining streaks down the finish.
• Lifting Over the Shop Primer: A high performance finish applied over an incompatible shop primer can lift, wrinkle or lose adhesion; field experience points to general purpose alkyd shop primers under two-component field finishes as a frequent cause.
• Touch-Up That Does Not Match: Steel is damaged in shipping and erection, and repairs made with a different material or poor technique stay visible for the life of the coating.

None of these conditions is unusual. Each one traces back to a system decision made before the steel reached the shop.

Life-Cycle Cost: Where the Money Actually Goes

When exposed steel needs repainting ahead of plan, the largest costs have little to do with coating material. Owners see them in four places:

• Access: Exposed steel is often overhead, above occupied space or above traffic, so repainting can require lifts, scaffolding, swing stages, lane closures or after-hours work.
• Preparation in Place: Cleaning and preparing steel after erection, around glazing, finishes and occupants, is slower and more limited than shop work, and containment adds time.
• Disruption: Tenants, visitors and operations are affected while work is under way, and in retail, hospitality or public buildings the appearance of the work zone is part of the cost.
• Lost Design Intent: A faded or stained structure changes how the building reads, and owners often act on appearance before corrosion forces the issue.

As a general estimate, the labor, access and disruption of an in-place repaint can far exceed the original difference between a basic system and a high performance system. That is why the system decision belongs at design, not in value engineering.

The HPC article Why High Performance Coatings Fail covers the broader causes of premature coating failure.

System Selection: The Decisions That Set the Outcome

Most of the outcome is fixed by a handful of decisions made before fabrication. Specifiers can control each one in the contract documents.

1. Exposure

The specification should define whether the steel is interior and conditioned, exterior, or exterior in a coastal or industrial setting. The ISO 12944-2 corrosivity categories give specifiers a recognized way to describe exterior exposure.

2. Surface Preparation

The primer determines the required cleaning level. Zinc-rich primers generally call for a minimum commercial blast cleaning (SSPC-SP 6/NACE No. 3), although the product data sheet and the coating system govern.

Edges, welds and weld spatter need attention before blasting. This matters most on architecturally exposed structural steel (AESS), where fabrication quality is visible.

3. Primer

For exterior exposures, a zinc-rich primer applied in the shop gives the system a corrosion-resistant base. It belongs in both the structural steel and painting sections so the fabricator and painting contractor work from the same system.

The HPC article Unlocking the Power of Zinc Primers in High Performance Coating Systems explains this coordination in detail.

4. Finish

The finish carries the appearance. Weatherable aliphatic polyurethanes and fluoropolymers are the two common choices for exposed exterior steel, and performance standards for weatherable urethane topcoats (SSPC Paint 36) and field-applied fluoropolymer topcoats (SSPC Paint 47) give specifiers performance-based language.

The HPC article Fluoropolymers or Polyurethanes: Making the Best Choice compares the two chemistries.

5. AESS Category and Gloss

The AISC Code of Standard Practice (ANSI/AISC 303-22), Section 10, sets AESS categories from AESS 1 through AESS 4 and AESS C. Higher categories invite closer viewing, and higher gloss finishes show surface variation more readily, so gloss should match the category and the lighting.

Specification Checklist: Requirements That Prevent Failure

A short list of requirements prevents most of the failures described above. Specifiers should include:

• Single-Source System: One coating system, primer through finish, from a single manufacturer, named in both Division 05 and Division 09.
• Preparation Standard: The surface preparation standard required by the primer, stated by name.
• Stripe Coats: Stripe coats on edges, welds, bolts and connections.
• Touch-Up Procedure: A defined procedure and material for shipping and erection damage, as described in Proper Methods for Touching Up High Performance Coatings.
• Weathering Requirement: A weathering performance requirement for the finish (SSPC Paint 36 or SSPC Paint 47), with a defined color and gloss standard.
• Mock-Up: A mock-up for AESS 3 and AESS 4 elements, viewed under project lighting.
• Film Thickness Inspection: Dry film thickness measurement (SSPC-PA 2) using gauges that meet ASTM D7091, with results submitted.
• No Primer Substitution: No change to the shop primer without written approval from the coating manufacturer and the design team.
  
  

Conclusion

The real cost of the wrong coating on architectural steel is the repaint nobody planned for, paid in access, preparation and disruption. We recommend selecting the system at design, naming the primer in both specification sections, requiring stripe coats and a touch-up procedure, and choosing a finish with documented weathering performance.

The best time to prevent a repaint is before the steel reaches the shop.

Field Verification Before Specifying

The following conditions are to be confirmed in the field with the applicable test before a system is finalized:

• Existing coating type and condition on exposed steel being repainted: visual assessment and coating identification by lab analysis where unknown.
• Existing dry film thickness: SSPC-PA 2 using ASTM D7091 gauges.
• Adhesion of existing coatings: ASTM D3359 (tape) or ASTM D4541 (pull-off).
• Hazardous materials in existing coatings (lead, chromium): lab analysis of samples.
• Soluble salts on prepared steel in coastal or deicing-salt exposures: SSPC-Guide 15 field methods.
• Surface profile after blasting: ASTM D4417.
• Shop primer identity and compatibility on delivered steel: fabricator submittals and a test patch where in doubt.

We are happy to help. Contact a High Performance Coating Consultant in your region to review your project conditions and specification.