You would be able to tell if you had rust under the coating on steel, It
would be a mound that would keep growing. Just like you would tell if your
car had a pinhole in the paint and it was rusting underneath. If the metal
is prepped correctly and applied the same it works well because it has some
flexibility and is resistant to chipping not allowing water to get
underneath.
I had the stuff sprayed on my pickup truck bed and it's great. My friend in
the construction business had it sprayed in his truck and beats it up good
and has a diesel tank in the bed that gets spills and it hasn't been
bothered in 4 years.
I don't know that I would use it underneath. How would you clean such a
rough surface?

"Paul Schilter" paulschilter@comcast,dot,net wrote in message
...
HL,
What do you mean by "steel deterioration beneath"? Beneath the
coating?
How do you tell if the bonding is complete and there is no moisture
intrusion. It would seem that by the time you seen damage to the steel
deck,
from below decks, the deck would be almost gone.
Paul