Salt Air and Why Stainless Is Not Optional in Florida

Why galvanized fails so fast here

Galvanized steel works by sacrifice. The zinc coating corrodes preferentially so the steel underneath does not, and in a dry climate that buys decades.

In continuous salt-laden humidity the zinc is consumed in a few years rather than a few decades, and once it is gone the steel goes quickly. On the coast a galvanized chase cover can perforate in three or four years. Inland in Florida it is slower, but it is still years rather than decades — which is the part people get wrong, because they assume being twenty miles from the beach is being inland.

The fixings fail first

This is the most common mistake. A stainless cap held with plated screws fails at the screws, and on an exposed stack that means a cap that leaves in the first storm. Ask what the fasteners are, not just the cap.

Orange streaks are the metal, not the masonry

Rust staining down stucco or siding is nearly always the corroding part above it. Masonry stains white — that is efflorescence, a mineral salt deposit, and it means something different.

What to specify, part by part

Four items, and the answer is the same for all of them.

The cap

Stainless, with stainless mesh and stainless fasteners, and mechanically fixed or clamped rather than resting on friction — because storm uplift is the other Florida variable.

The chase cover

Stainless with a pressed cross-break so water sheds to the edges instead of ponding in the middle. A flat galvanized cover is the builder-fitted default and it is the single most common Florida chimney repair.

The flashing

Properly detailed metal let into a reglet, not sealant. Sealant degrades fast under Florida sun regardless of what is under it.

Anything on a direct-vent terminal

The exterior terminal of a sealed gas appliance is metal, outdoors, permanently in salt air, and nobody ever looks at it. Corroded or obstructed, it is a venting fault.

What salt does to masonry and render

Metal is the obvious victim. Masonry suffers differently and more slowly.

Salt-laden water moving through masonry leaves crystalline deposits as it evaporates — that is efflorescence, and while the deposit is harmless the water that carried it is not. In a climate where masonry never fully dries, mortar loses its binder faster and any steel embedded in it corrodes and expands.

The product that helps is a breathable siloxane repellent on sound masonry or render. The product that actively harms is a film-forming sealant, because it traps moisture against a substrate that needs to dry. On a Florida chimney that distinction matters more than almost anywhere.