A sanding block was used to make sure we didn’t add ripples to the surface of the part. A foam block was used to get inside the duct and for nonstraight surfaces. Just sanding without a block will make the part ripplely.
Once we had the tops of the print lines knocked down, we used a coat of XTC-3D epoxy to fill the groves and gaps to make a smooth surface.
We brushed on a couple of coats of the XTC-3D using a little less than recommended hardener so it could flow out longer to get rid of brush marks as much as posible.
Again we sanded with 220 open-coat sandpaper with sanding blocks to leave a smooth surface.