Z275 vs Z450: How to Keep Your Coastal Warranty (and Your Sanity)

Coastal job, 300 m from the surf, owner wants a 30-year warranty but the budget looks like it was written in 2015. Sound familiar?

Here’s the no-BS field note:

• Z275 = ~20 µm per side. Fine if you’re inland or you like repainting every decade.
• Z450 = ~40 µm per side. That’s double the sacrificial zinc, double the time before first maintenance.

Yes, Z450 adds maybe $120/t on a typical portal frame. On a 100 t building that’s $12 k—cheaper than one rope-access repaint cycle at year 12.

Warranty secret nobody prints: coating thickness gets you in the door, but the warranty underwriter also wants:

1. No ponding details (drain those gutters!)
2. Wash-down access (owner has to hose it twice a year)
3. Top-coat friendly—add a 60 µm epoxy seal and you’ll sleep at night.

So if the RFQ says “C5-M environment” and your kids’ college fund depends on no come-back claims, just bite the bullet and spec Z450. Future-you (and the facility manager) will buy you a beer.