How to Paint Doors
To paint doors, start by taking them off the hinges and putting tape around the edges of the fixtures. Next, apply primer to both sides of the doors. Once the primer is dry, use a roller to paint the surface on either side, and a paintbrush for any narrow spaces in the paneling. After the paint dries, flip the doors over and repeat the process on the reverse side. Finish with a second coat of paint, if needed, before reinstalling your doors.
Gather your door painting supplies. Obviously, you'll need a paintbrush and paint, but for best results, you'll likely also want a suitable primer. Be sure the paint and primer you buy is intended for your purposes ( interior vs. exterior; acrylic vs. oil based), and, all in all, be sure you also have: Clean rag Drop cloth(s) (or newspaper) Hammer Latex paint (or other suitable paint) Paintbrush Paint tray (for roller) Primer (if necessary) Roller (low-nap) Sandpaper (fine grit, 180 - 220-grit) Sawhorses Screwdriver Use your hammer and a screwdriver to remove the hinge pins. First, close the door so the hinge opens flat, allowing better access. Then, use a small screwdriver to force the pins out of your hinge. You may only need a screwdriver to accomplish this task, but if the pin is stuck, tap the back of your screwdriver with a hammer to pop it free. If you don't have a screwdriver the right size on hand, you might try using a nail pushed through the bottom of the hinge. Have a friend help remove the door. The shape of your door and the material it's made from can make handling a door by yourself cumbersome, difficult, or dangerous. Especially if you are painting a metal door, which can be extremely heavy. Once the pins have been pulled free from all hinges, remove the door from its frame with your helper. Position the door in your work area. Make sure the area you will be painting is well ventilated, clear of obstacles, and properly covered with drop cloths or newspaper in case of drips or splatter. Laying your door atop sawhorses with the side you intend on working face up will make the sanding and priming process easier on yourself. You can lay the door on the floor, if necessary, but this can dirty your door or accidentally cause damage. To prevent your door from sticking or freshly applied paint from becoming damaged by your sawhorse, you may want to use cardboard to pad the tops of your horses. Sanding and painting bent over might also cause back pain. Remove or tape around the edges of fixtures. To ensure your doorknobs don't get primed or painted during this process, you should remove handles and any other features, like clothes hooks, from your door. If you do not plan on removing these from your door, you might: Prevent hardware from being painted by taping around the edges of fixtures, or even taping the entire fixture. Sand the door lightly. Use fine grit sandpaper, between 180 and 220-grit, while stripping old, flaking paint and smoothing rough edges. A power sander or coarse sandpaper might cause scoring in your door, leaving unsightly notches or lines in its surface. Clean your door, if necessary. Your door may have accumulated some dust or grit in the sanding process. Take a clean rag or paper towel and wipe your door free of any dust, dirt, or grime. Do not use water. If water soaks into the material of your door, it can have a negative effect on how the primer and paint bond to the surface. Repeat sanding and cleaning on both sides. By tackling your door one side at a time, you accomplish two goals at once. Your careful attention to one side at a time will help ensure evenness and consistency for the whole door. This will help you achieve a professional looking finished product. Prime your door. Primer helps to prepare the surface of your door for the actual coat of paint. Some surfaces, especially those that are rough or absorbent, can be difficult or expensive to paint if unprimed. You'll certainly want to prime your door if: Your surface is unfinished. Your door is made of bare or stained wood. You want to paint the door a color lighter than its current color. Allow your primer to rest. The specific brand of primer that you bought should have instructions for how long you should let your primer dry before applying paint. Follow these directions for best results, but when in doubt, allow 48 hours to pass before applying your paint. Prime the reverse side of your door. But first, you should give it a once over to make sure that it is clean. Dirt or dust that might have been on your sawhorses could have rubbed off on your door. Using a clean rag or paper towel, wipe any dust or grit off the door before priming. Be sure not to get your door wet. Wetness on the door can prevent your primer and paint from bonding with its surface. Prepare to use your roller. Rollers are intended to cover a large area with paint efficiently. To cut down on the time you spend painting, put a moderate amount of paint in your tray. Then: Place your roller into the trough of your tray until it is half saturated with paint. Roll it on the groves to remove excess paint. Do this several times to thoroughly wet the nap of your roller. Apply enough paint so the roller is wet through but not dripping. Now you're ready to roll! Paint panels with your roller. A small roller should help you work quickly while still providing enough maneuverability to get as much of the edges as you can. The panels are the inner shapes carved into the door, and should be focused on first. Use moderate force when rolling; pressing too hard can cause paint to bead along the outer edge of your roller. Dip your paintbrush into your paint can and use the tip of it to get any narrow spaces in the paneling your roller cannot reach. Use your brush to smooth any heavy areas or dribbles. Do this by wiping free excess paint on the inner lip of your paint can, wiping the excess paint off the door, and wiping the excess paint back onto the inner lip. Be especially vigilant for buildup in corner and edges. Use your roller to paint the crossbar. Generally, you should follow the direction of the bar for the best effect. When painting a vertical bar or brace, use vertical motions with your roller. The opposite should be done for horizontal bars. Paint the border of your door. Move your roller in an up and down motion to paint the left and right sides of your door. Then, using a left-to-right motion, paint the top and bottom borders. When painting edges with a roller, extra paint caught in the nap of your roller sometimes squeezes out, causing a run line or thick area. Keep your eyes peeled and a brush handy to correct run lines or thick areas. Add finishing touches using your paintbrush. Your paintbrush will allow you to paint difficult areas of your door with much greater detail and control. Use your brush to clean up edges where paint has collected and smooth out any unevenness in the paint. If painting a wooden door, paint with the grain, which is the direction the wood appears to flow in. Allow the paint to dry. The directions on your paint can should indicate how long you should let your paint dry before adding a second coat, but if you are unsure how long you should wait: Wait 30 minutes for light coats and thinner paints. Wait four hours for thicker coats and medium thickness paints. Wait more than four hours for especially thick paints. Paint the reverse side of your door. Now that the topside of your door is painted and dry, you should flip the door and repeat the painting process on the other side. This time, you should be mindful of: Edges, where excess paint might drip from your roller and dribble onto the other side. Gaps in the wood. Some panels or wooden doors are constructed with some space or looseness where two pieces of wood form a seam. Paint these sections lightly with a paintbrush to prevent buildup on the opposite side. Apply a second layer of paint. A second layer of paint can help bring out the luster in your paint, and can be especially useful at covering up any bleed through from your primer. Make sure that your paint is completely dry before applying the second coat. Allow the door to dry completely. Now that both coats have been applied, you should inspect the door for any errant drips or thick spots. Use your paintbrush to smooth these out, and then consult your paint can to find the recommended wait time till dry. Set an alarm so that you can check your door to see if it's done drying. If the paint is wet, damn, or feels poorly bonded, reset your timer and wait another 30 minutes. Do this until the paint feels dry. Depending on the quality of your paint and door, you may want to sand very lightly with fine grit sandpaper between coats. Lift the door back into its original position. You may need a helper to do this, especially if the door is heavy or cumbersome. But now that you're satisfied with the paint job and the paint has fully dried on both sides, you can reinstall your door. With your helper: Slide the door into place so that the door hinge slots into the wall hinge. Have your helper hold the door steady while you reinsert hinge pins. Use a hammer or the handle of your screwdriver to tap stubborn pins into place. Check the levelness of your door, if having difficulties. Holding the door at even a slight angle can make it impossible to reinsert hinge pins. 
Gather your door painting supplies. Use your hammer and a screwdriver to remove the hinge pins. Have a friend help remove the door. Position the door in your work area. Remove or tape around the edges of fixtures. Sand the door lightly. Clean your door, if necessary. Repeat sanding and cleaning on both sides. Prime your door. Allow your primer to rest. Prime the reverse side of your door. Prepare to use your roller. Paint panels with your roller. Use your roller to paint the crossbar. Paint the border of your door. Add finishing touches using your paintbrush. Allow the paint to dry. Paint the reverse side of your door. Apply a second layer of paint. Allow the door to dry completely. Lift the door back into its original position. 