You bought a fiberglass door for performance and durability, now you want to make it look great. But, typical wood stains won't absorb on fiberglass and can leave you with streaks and drips.
First: Prep the door. Using a clean, dry rag, clean the entire surface with the mineral spirits provided in the kit or an all-purpose cleaner. After rinsing, allow the door to dry completely. Then use masking tape to cover any glass, and remove or mask hinges, lock hardware and weatherstripping. Do not use turpentine and do not sand the door.
Second: Stain the door. Dip the staining cloth in the stain and rub the stain on the door in a circular motion. Apply the stain to the panels. Next, stain the "rails" or short, horizontal sections. Finally, stain the long vertical stiles that run along the left and right sides of the door.
To obtain a light stain, wait about five minutes and then brush the stain out strongly with the tips of a natural bristle brush. For a dark stain, wait about ten minutes and brush the stain lightly. Feather the stain in the direction of the grain to obtain a uniform color. Wipe any excess stain from the brush onto a dry cloth.
Third: Seal the door. Allow the stain to dry for 48 hours. Then apply a very thin coat of protective topcoat/sealer. Wet only the tip of the brush and brush in the direction of the grain. Cover all door surfaces, working in the same order in which you applied the stain. The surfaces should look wet, but not milky. Wait three hours for the first coat to dry. Then apply a second, very thin, even coat.