How to Finish Pella Factory-Stained Fiberglass Entry Doors

Remove the hardware, such as knobs, latch plates, knockers and hinges, from your Pella door with a screwdriver -- check the hardware to see which type of screwdriver you will need. If there are any window panes, cover them with painter's tape and plastic to prevent the polyurethane from getting on the glass.

Wash the door thoroughly with hot water mixed with a mild detergent. If this is a wood-look door, pay particular attention to the grooves of the simulated wood grain. This will remove any dust that might get trapped under the finish.

Stir the polyurethane gently with a wooden paint stirrer. Use a polyurethane that is formulated for exterior surfaces. Spar polyurethane may also be used -- this is a type of polyurethane typically used on sailboat spars, which are often made of fiberglass or wood. Pour the polyurethane into a clean paint tray or small bucket.

Dip a foam or lamb's wool applicator in the polyurethane. Strike the applicator against the upper portion of the paint tray or the inside of the bucket to remove the excess -- avoid wiping the excess off, as this can remove too much polyurethane and give you an uneven finish.

Spread the polyurethane over the door. If it is a wood-look door, work with the simulated grain. Otherwise, make uniform strokes that go in the same direction for smooth panels. Coat the entire door, then allow it to dry.

Sand the door gently with very fine-grade sandpaper, around 400-grit or higher. Wipe away the polyurethane dust. Apply a second coat of polyurethane to the door before installing it in its frame.