The three-coat system, and the overcoat decision
On Pittsburgh's bridges and structural steel the coating carries the corrosion protection, and it's specified to the ISO 12944 C4–C5 environment the steel lives in. The workhorse is a zinc-rich three-coat system, applied to a per-coat dry film thickness that adds up to the design DFT. The other decision is strategy: strip to bare steel and rebuild, or overcoat sound existing paint where full containment isn't practical.
| Coat | Product | DFT per coat |
|---|---|---|
| Primer | Inorganic or organic zinc-rich (IOZ) | 3–5 mil |
| Intermediate | High-build epoxy | 4–8 mil |
| Topcoat | Aliphatic polyurethane | 2–4 mil |
For an in-service structure that can't take full blasting, a moisture-cured urethane (MCU) overcoat goes over the cleaned existing system instead — trading maximum life for less disruption and no containment of a full removal.
Who we serve around Pittsburgh
Bridge and structural steel, water and wastewater infrastructure, steel mills and heavy manufacturing, and Marcellus natural-gas equipment.
What this means for your project
The system and its film build set the corrosion life, and the recoat-vs-overcoat call sets the cost and disruption. Describe the structure and its condition — we'll pair you with a Pittsburgh contractor who paints bridge and structural steel.