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Paint can permanently damage your surfaces, so it's important to protect them before you begin. Put down newspapers, a drop cloth, or a tarp and then put your chairs on top of it.  If you use newspapers, put down a thick layer of them, such as 7 to 10 sheets stacked on top of each other and overlapping with several other stacks of 7 to 10 sheets. Make sure the area is well-ventilated before you begin painting, too. Open windows and turn on a fan to help increase the air circulation. You may also want to wear a mask to protect yourself from the paint fumes. If your chair has a fabric seat, such as a dining room chair, then you will need to unscrew it from the chair and set it aside before you start painting. Turn the chair upside down, locate the screws, and use a screwdriver to unscrew them. Place the seats well away from where you will be painting the chair. If the seat covers are old or damaged, then you may want to reupholster the chairs as part of this project. Use a coarse, 80 to 100-grit piece of sandpaper if there's any old paint or lacquer on the piece that you need to remove. Then, switch to a 150-grit or above sandpaper to smooth out any rough spots on the chairs. Rub all of the surfaces of each of your chairs with the sandpaper. Use a back and forth motion to sand them on the seat, spindles, back, legs, and sides. Keep sanding until the surface of each chair is smooth.  Sanding is an important part of the process since it will work out any minor imperfections in the wood and help to make the paint look nicer on the finished chair. You can sand manually or with an orbital sander. Blow on the chair or use a dry cloth first to remove the loose dust left over from sanding it. You can also vacuum up the remaining dust on the chair. Then, wet a washcloth with water and wring it out. Wipe the chair all over with the cloth to remove the remaining dust. Don't skip this or you will end up with dust particles in your paint, which can give the chair a rough appearance. Use a clean, bristled paint brush to apply primer to all surfaces of the wood chairs. Use smooth, long strokes over large surfaces, and short, back and forth strokes over smaller areas.  This will help to create a smooth surface to apply your colored paint onto. The primer will also help the color of your paint to stand out more.  The primer will look like a matte white or grey color. Check the manufacturer's instructions to see if primer is recommended with your paint. Not all paints require you to use a primer, but your results might be better if you use primer. The primer packaging should indicate how long to wait between your coats of primer and paint. Follow these recommendations. However, you may only need to wait about 10 minutes for a thin coat of primer to dry, so the primer you applied to the first chair might be dry by the time you finish painting primer on the last chair. Check the manufacturer's instructions to be sure about how long you should wait between coats of primer, and also how long to wait until you apply your paint. If the primer has left the surface of your chair looking uneven or feeling rough, then you may need to sand it again using a fine-grit (150 or higher) sandpaper. Rub the sandpaper back and forth over each of the chairs to smooth out their surfaces. Make sure to wait until the primer has dried completely before you sand the chairs. Use a clean, bristled paint brush to apply the colored paint to the surface of your chairs in a very thin layer. Apply the paint to large surfaces of the chair using long strokes and to smaller areas with short, back and forth motions.  Wait the recommended amount of time for the first coat of paint to dry. Then, apply a second thin coat of paint onto each of the chairs. Check the label on your paint can for instructions on how long you need to wait between coats. Some paints dry quickly and the first chair you painted may be dry by the time you finish painting the last chair, so you might not have to wait long at all to apply your next coat of paint. Check the manufacturer's recommendation for how long to wait after you finish painting the chairs. The paint might dry within a few hours, or you might need to wait longer for it to dry completely. To be sure that the chairs are completely dry, plan to wait to move or use the chairs for 24 hours after you apply the last coat of paint.  Keep pets and children away from the chairs while the paint dries. Close the door to the room you painted them in or block off the area so that children and pets cannot access it. If the weather is humid where you live, then the paint may take longer to dry.

Summary:
Protect your surfaces with a drop cloth, tarp, or old newspapers. Remove any fabric seat covers from the chair before you begin. Sand all surfaces of the wooden chairs. Wipe down the chairs with a damp cloth. Apply 1 coat of primer to each of the chairs. Allow the primer to dry as indicated by the manufacturer. Sand and dust the chairs again after the primer is dry if needed. Apply 2 or more thin coats of paint to the chairs. Allow the paint to dry completely before using the chairs.