When you are thinking about painting a brick exterior, consider the benefits of whitewashing instead. Not only can you whitewash a brick surface, but it is much better than painting. Modern outdoor paints stick to brick really well for a while, but wear quickly and unattractively. Paint peels and flakes after only a year. However, whitewash on a brick surface penetrates deeply causing it to last much longer. When whitewash does fade, it does so more naturally than paint. Whitewash remains attractive even after it has faded substantially.
Whitewash requires a different process than painting.
Step 1 - Prepare
The brick surface needs to be sanded down. Scrape or sand off any previous paint and then sand down the surface to be whitewashed until it is smooth. Be sure to cover any other surfaces you do not want whitewashed including the ground. Whitewash penetrates deeply and quickly, making it nearly impossible to remove.
Step 2 - Clean the Surface
Scrub the brick surface thoroughly with soap and water and a good, stiff brush. Any dirt or oil will be very noticeable through the whitewash. Rinse with clean water. Allow the brick to dry completely if you desire a smooth, consistent finish. If you want a more textured finish, applying whitewash to a wet brick can achieve an attractive effect.
Step 3 - Apply
Applying whitewash requires a different technique than standard painting. Use a large paintbrush, but rather than long, smooth strokes, apply the whitewash with quick, rough strokes. Jab the bristles against the brick to get it into all the divots. Only allow the ends of the bristles to make contact with the surface.
Again, if a textured finish is desired, vary the thickness of whitewash, but be careful not to allow drips.