How to Restain an Exterior Door

Take off all of the hardware from the door, including hinges and doorknobs. Set the door up on a clean worktable. Clamp the door down or work with a partner to keep it from moving while you sand.

Strip the old finish and stain with an orbital sander fitted with a 100-grit sanding pad. If you don't have an orbital sander or are uncomfortable with the idea of using one, you may do this by hand, but it will take much longer to complete the project.

Sand both sides and all four edges of the door and then wipe it down with a damp cloth. Sand the door again with a 220-grit sanding pad. Wipe the door down with a fresh, damp cloth.

Apply wood stain designed for exterior surfaces. The word "Exterior" will appear on the label, and the product will most likely be oil-based. You can apply stain with a paint roller, paintbrush, paint sprayer or a simple cotton cloth. Always work with the grain. Let the stain soak into the wood for about five minutes and then wipe the door down with a dry cloth.

Allow the stain to dry completely. Ensure that both sides and all edges are completely coated. If necessary or desired, apply additional coats of stain.

Apply polyurethane designed for exterior surfaces. As with the stain, the product will likely be oil-based, but it may be solvent-based instead. Both options are fine for exterior doors.

Mix the polyurethane well by stirring it and then pour a small amount directly on the door. Spread the polyurethane with a lamb's wool or foam applicator. Spread it evenly and as thinly as possible. Always slide the applicator along the grain of the wood, never against it.

Allow the polyurethane to dry completely. Once it is dry, flip the door over and repeat the process for the opposite side of the door. Allow this side of the door to dry. When working on either side of the door, remember to apply polyurethane to all of the edges.

Scratch the surface of the polyurethane with super fine-grade sandpaper, at least 400-grit or higher. This will smooth out any finger prints and give the next application a better surface to cling to. Apply three or four more coats of polyurethane, using the same process.

Reattach any hardware once the polyurethane is completely dry on both sides of the door. Install the door back in its frame.