Hollow-core doors can be an attractive design element in any home after they've been properly stained and sealed. Unfortunately, the most popular stain variety -- penetrating wood stain -- can produce a splotchy appearance on wood. Gel stain is a better option for the wood veneer skin of a hollow-core door because it provides an even coating of translucent wood-tone color. Gel stains are also easier to apply to vertical surfaces -- less dripping -- making it possible to stain doors in place, if you prefer not to remove them.
Remove the door from its hinges using a screwdriver and hammer to tap out the hinge pins (or you can leave the door in place, if desired). Set the door on sawhorses and remove the hinge leaves from the door. Also remove the doorknob, using a screwdriver. You can remove the latch mechanism from the door's edge, if desired, or leave it in place.
Smooth out any surface irregularities by sanding the door's wood veneer skin with 180-grit sandpaper. Remove any dust or debris by wiping the wood with a tack cloth.
Apply the gel stain to the door using a clean, lint-free cotton cloth -- such as an old T-shirt or a new cotton shop cloth. Starting from the top, rub the stain into the wood using a circular motion, until one entire side of the door is complete. Apply the stain evenly and wipe off any excess stain before it dries in place.
Repeat Step 3 on the opposite side of the door. Finish by wiping the gel stain on the door's edges and top.
Allow at least 12 hours for the gel stain to dry completely. If the color appears too thin or too light, apply a second coat. Let the stain dry as directed by the manufacturer.
Protect your newly stained door with an oil-based clear polyurethane finish coat (or other protective finish). The polyurethane seals the stained wood and protects it from scratches and abrasion. Most products call for at least two coats for best results, often requiring light sanding between coats; follow the manufacturer's directions for application.