Urethane primers can definitely stick to galvanized surfaces, but honestly, prep is key. Galvanized metal has that slick zinc coating, and if you don't rough it up a bit or use an etching primer first, adhesion can be hit-or-miss. I've seen some urethane-based primers peel off galvanized roofs after just a couple seasons because the prep wasn't thorough enough.
On the other hand, when properly prepped—like giving the surface a good scrub-down with vinegar or using a specialized metal cleaner—urethane primers can actually bond pretty well. I've had decent luck with them on smaller galvanized flashing pieces around skylights and vents, especially in areas with lots of thermal expansion.
But now you've got me curious... what kind of climate are you dealing with? If you're somewhere with extreme temperature swings, you might want to look into elastomeric coatings too—they're flexible enough to handle movement without cracking or peeling as easily.
I've gotta say, urethane primers can be solid, but honestly, elastomeric coatings aren't always the magic bullet either. I tried one on my shed roof (galvanized metal) thinking it'd handle our crazy Midwest temperature swings better... and it did flex nicely, but dirt and grime stuck to it like crazy. Ended up looking pretty rough after just a year or two. Personally, I'd stick with urethane primer—just spend extra time on prep and maybe test a small area first.
"Ended up looking pretty rough after just a year or two."
Yeah, elastomeric coatings can be a double-edged sword. I had a similar experience after a hailstorm trashed my barn roof. Thought elastomeric would be perfect since it flexes nicely with temp swings and impacts... but man, did it attract dirt and algae fast. Looked like it'd been up there forever after just one season. Urethane primer with careful prep definitely gave me better results long-term, even if it's a bit more tedious at first.
"Thought elastomeric would be perfect since it flexes nicely with temp swings and impacts... but man, did it attract dirt and algae fast."
Yeah, I learned that lesson the hard way too. A few years back, I put elastomeric coating on my shed roof thinking it'd be a quick fix—easy to apply, flexible, seemed like a no-brainer. But after one rainy season, it looked like I'd painted it with swamp water. Dirt and grime stuck to it like glue, and cleaning it off was a total pain.
Ended up stripping it down and going with a urethane-based solution as well. Definitely more prep involved, but it's held up way better over time. I guess sometimes the shortcut ends up being the long way around... who knew roofs could be so picky?
Interesting experiences, but I've gotta say elastomeric coatings aren't always the villain here. I've seen them perform pretty well on certain roofs, especially if you take some extra steps beforehand. The algae and dirt issue usually pops up when the coating is applied without proper surface prep or when the roof doesn't have good drainage. Elastomeric coatings are naturally more porous, so yeah, they're gonna trap dirt and moisture if they're sitting flat or in shady, damp conditions.
A couple years back, I helped a friend coat his metal roof with elastomeric, and we made sure to thoroughly clean and prime the surface first. We also adjusted the slope slightly to improve runoff. It's been holding up pretty well since then—minimal algae growth, and dirt washes off pretty easily with a quick hose-down every now and then.
Not saying urethane isn't a solid choice—it definitely is—but elastomeric isn't automatically a bad call either. It just needs the right conditions and prep work to shine. If your roof tends to stay damp or shaded, then yeah, urethane or silicone might be better long-term. But if you've got decent sun exposure and good drainage, elastomeric can still be a practical, cost-effective option.
Just my two cents from what I've seen. Roofs can definitely be picky, but sometimes it's about matching the material to the situation rather than writing it off completely.