Textured walls add depth and character to a room, as well as covering up any defects in construction. The technique for painting a textured wall isn't much different than that for any other wall, except that it takes a little more time and a little more paint to make sure every bit is covered. The big difference is in preparation, to prevent the paint from looking blotchy.
In order for the paint to stick tightly, there can't be any dust or loose texture material left on the wall. During construction and the texture application process, a large amount of dust is often created from cutting and installing drywall as well sanding. This dust settles on the wall, but isn't easy to see because it is the same color as the wall. Also, not all of the texture material adheres like it should, and small pieces may flake off easily. Wipe the wall with a clean, damp rag to remove all of the dust. Pay attention to any areas where little pieces of the texture material come off during cleaning, and scrub those areas a little bit harder to make sure all the loose material comes off before painting.
The heavier the texture, the more difficult it will be to get paint into every nook and cranny. Rollers with a thick nap are designed to get into textured areas and provide full coverage. Choose a roller with a nap that is at least 1/2-inch thick for most textures. For deep textures, look for rollers with a 3/4- to 1-inch nap. Use a high-quality natural bristle brush to get into corners and especially deep crevices that no roller will reach.
Prepare a textured wall for painting the same way as any other wall, by patching any nail holes or blemishes, removing outlet covers, and taping around windows, doors, and any other areas that won't be painted. In addition, take a close look at the texture and make sure there aren't any rough or high points that look out of place. Sand any of these blemishes away with medium-grit sandpaper and then wipe away the dust with a damp rag. Place a drop cloth on the floor to catch any drips.
A coat of primer is sometimes optional if the textured wall has been previously painted. It is mandatory, however, when painting a freshly textured wall. This is because the texture medium will absorb the paint as it is applied, resulting in blotchy, uneven color. Use a primer designed for new construction, such as a wallboard primer, which will create a barrier that prevents paint from soaking into the texture.
Use a brush to cut in, or paint around the edges and corners where a paint roller won't give good coverage. Then apply paint to the rest of the wall with a roller, working in sections and moving the roller in various directions to push paint into all the crevices. If the roller isn't pushing the paint into heavily textured areas, use a brush to get the paint into the crevices, and then go over the same area immediately with a roller to get an even finish. Let the first coat dry at least three hours and then apply a second coat using the same method.