The grate is printed in a plastic material called Frosted Extreme Detail (FXD). I really do not need the fine detailing possible with that material. I could have used the Frosted Ultra Detail (FUD) instead, but the FXD also gives a smoother surface which I wanted.
As you can see my printing includes the concrete parts of the grate only. To make the 3D model simpler I decided to not include the metal framing but to add that later using styrene dimensional strips. The next photo shows just that.
And the completed assembly painted with a grey spay primer.