Your experience sounds familiar—had a similar thing happen at my parents' beach cottage. My dad thought marine coatings were foolproof, too, but he underestimated how sneaky moisture could be. Turns out, prepping properly isn't just sanding and priming; it's about timing the application just right. Even slight humidity or dew that forms overnight can mess things up. The isolation tape trick is smart though...wish we'd known about that earlier. Coastal living definitely keeps you on your toes.
Had a similar issue with my metal roof near the coast. Thought I had it all figured out after applying marine-grade paint, but nope—salt air and moisture still found their way in. You're right about timing being crucial. I learned the hard way that painting too late in the day, even if it feels dry, can trap moisture underneath. Now I always aim for mid-morning applications after the dew has fully evaporated.
Also, isolation tape is great, but I've found adding stainless steel fasteners and fittings makes a huge difference long-term. Regular galvanized stuff just doesn't cut it near saltwater. Costs a bit more upfront, but saves headaches down the road.
Coastal living definitely teaches you to be proactive...and patient.
Marine-grade paint helps, but it's not a silver bullet. I've found that adding a breathable underlayment beneath the metal panels can really help manage moisture buildup. Stainless steel fasteners are definitely worth the extra cost—galvanized hardware just corrodes way too quickly near saltwater. Also, regular rinsing with fresh water every few months can slow down corrosion significantly...sounds tedious, but it pays off in the long run.
Good points there, especially about the stainless steel fasteners. Galvanized hardware might seem okay at first, but I've seen it fail surprisingly fast near the coast. Stainless steel is definitely the way to go if you don't want callbacks or headaches later.
One thing I'd add from experience: ventilation matters more than people think. Even with breathable underlayment, if there's not enough airflow under the panels, moisture and salt can build up and start eating away at the metal from underneath. I've seen roofs that looked perfect on top but were rusting badly underneath after just a few years because of poor ventilation.
Another tip—if budget allows—is considering aluminum roofing panels. Aluminum holds up better than steel in coastal areas because it doesn't rust. Sure, it can oxidize, but that's mostly cosmetic and actually protects the metal underneath. It's pricier upfront, but I've had clients who went aluminum and haven't regretted it one bit.
And yeah, rinsing regularly is a chore, but you're spot-on—it really does pay off. Had a homeowner who religiously rinsed his metal roof every few months, and after 10 years, it looked nearly new compared to neighbors who didn't bother. It's a hassle, but corrosion prevention is always cheaper than replacement.
Interesting points, but is aluminum really worth the extra cost in every coastal situation? Worked on a job last summer where the homeowner insisted on aluminum panels. Sure, they held up great against corrosion, but we had issues with dents and scratches during installation—stuff I never saw with steel. Maybe we were just unlucky, but it made me wonder if aluminum's durability trade-off is always justified, especially if you're careful about ventilation and rinsing regularly...
