Porch Overhang material

I live in Tampa, FL and have an entry way overhang at my front door. I was pressure washing the overhang and some of the material came off; almost like a thin plaster. It looks like some kind of exterior drywall is behind it?? My question is, what most likely is the "drywall" and what kind of coating would be on top of it?
Thanks for any info.
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