What it is: Bare steel that is phosphatized (chemically treated to help paint bond to it) and has a primer coat of paint on the underside.
Phosphatized and painted composite steel deck exists because the unit price of cold rolled bare steel with a primer is less than galvanized steel. However, painting the top of composite floor deck would inhibit the composite action it was designed for because the paint does not form a chemical bond with the concrete like galvanized or lightly rusted bare steels do.
This means two things:
1. The top cannot be painted and
2. The top needs to develop light tight rust for the deck to work.