Metal roof: coat it or replace it?

Yes, provided the rust has not gone through the panel. Corrosion is wire-brushed or ground back to sound metal and spot-primed with a rust-inhibiting primer before anything else happens, which arrests it rather than hiding it. Where rust has perforated panels or eaten through at the purlin line, those panels are replaced first — a coating bridges a pinhole, not a hole you can see daylight through.

Because the screws were only ever sealed by a neoprene washer, and those washers have a shorter life than the panels. They harden, crack and shrink, and the daily thermal movement of the metal backs the screws out slightly. A screw-down roof can carry tens of thousands of fasteners, so it does not develop one leak — it develops thousands of potential ones at roughly the same time. That is why fastener replacement and sealing is the core of a metal restoration, not an extra.

Slope and drainage decide. A sloped metal roof that drains freely and never ponds is a good candidate for a reflective acrylic system, which costs less and performs well in that condition — that is what we specified on the Touch Tape corrugated roof in St. Augustine. Low-slope metal, any area where water stands, or a roof with transitions into flat sections needs silicone, because acrylic re-emulsifies under standing water. Metal is the one assembly where we genuinely specify both.

On an uninsulated or lightly insulated metal building the difference is noticeable, because you are changing the temperature of the ceiling itself. A bare or faded metal roof in Florida sun runs extremely hot and radiates that heat straight down into the space; a reflective white finish rejects most of the solar load instead. We will not quote you a percentage, because it depends on your insulation, your HVAC and how the building is used — but it is the one benefit metal-building owners consistently report back to us unprompted.

Yes, and the transition between them is the part that matters. Those junctions are where mismatched materials, different movement rates and awkward drainage meet, and they leak more often than either roof does. A single silicone system can run across both, which removes the transition detail as a separate point of failure. The Goodyear hangar was exactly this case — metal and built-up on one building, restored as one system.