Wood isn't the only material that can take a stain. People often stain steel doors to give them a more dynamic look. The best way to color a steel door is with a gel stain. Gel stains are thick and designed to cling to and penetrate the surface. Once applied, they settle into the grain of the steel door to give it a textured look. In fact, gel stains are often applied to give steel doors the look of wood grain. Gel stain is easy to apply but it sets fast. Have all of your supplies on hand. You can't leave the area once the gel stain goes on.
Remove any hardware from the door. Stain it separately, if desired.
Lay the door out on a canvas in a suitable work area. Outdoors is best. This can be messy work.
Scuff the surface of the steel door with steel wool. The idea is just to roughen the surface to the touch so that it will readily accept stain.
Brush and sweep any sanding shavings away from the area.
Mix a solution of 1 part vinegar, five parts water. Put on a pair of clean gloves to keep your fingerprints off of the door. Dip a soft, clean cloth in the solution and use it to wipe the door clean.
Stir the gel stain thoroughly.
Pour roughly 1 cup of the gel stain into a separate container. Never dip the roller into the main supply.
Paint a layer of stain onto the steel door with the roller. Use the angled brush to get into any nooks, crannies or edges. Work in the direction of the steel's grain. Work quickly. Most gel stains begin to set in a matter of one to two minutes. Don't brush over set stain or it will lift from the steel and fail to penetrate. To make sure that you work within the drying time, work in 4-foot-by-2-foot sections at a time.
Allow the stain to set for the manufacturer-recommended amount of time, which is usually three minutes.
Wipe the stain off the steel with a clean rag.
Allow the stain to dry for 24 hours or the manufacturer-recommended amount of time before applying a second coat if desired. First United Door Technologies recommends applying two coats of stain on light-colored doors and three coats of stain on darker colored doors.
Apply and remove a second coat of stain in the same manner as the first coat. To create the look of wood grain, apply the second coat at a 90-degree angle to the first, against the grain of the steel.
Allow the stain to dry for 24 hours or the manufacturer-recommended amount of time. Apply subsequent coats if desired. Allow the stain to cure for 48 hours or the manufacturer-recommended amount of time before attaching the hardware and replacing the door.