Finishing an Exterior Door, Ep. 1: Sanding and Prepping the Door
Although often rushed or skipped completely, hand sanding is crucial.
Sanding and Prepping the Door: Never assume that a factory-fresh wooden door is ready for finish. You have to go over every square inch with sandpaper, starting at 150 grit with a random-orbit sander, and then working through 180 grit and 220 grit by hand. Be on the lookout for dents, scratches, and splinters, all of which should be dealt with before you start the dye phase.
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Fabulous Finish for an Exterior Door