The house is a ranch built on slab on grade with a newer furnace in a downflow configuration with A/C. The in-floor clay tile supply lines are in good shape and clean.
The original 60 year old in-floor supply plenum (30in x 22in) shows corrosion. The plenum is directly below the A-Coil & subject to condensate.
I have wire brushed the surface rust and treated it with
The Must for Rust. I am looking at various cold galvanizing compounds (
Rustoleum) to apply to the bare metal to restore the zinc protection. Access to the plenum (which is much larger than the 14in x 19in cabinet housing the A-Coil) is tight so this will be a challenge.
My concern is that since there are mixed metals in close proximity, a zinc coating may be important to protect the noble metal of the A-Coil by sacrificing itself to the eventual rusting process. Or does this even apply given that plenums are now sometimes fabricated with duct board?
I am wondering if I can just reline the bottom with a thin rubber mat cut to size that will conform itself to the metal isolating it from moisture from possible condensate from above?