Painting the barn is essential in preventing decay and weathering. You aren't limited to the traditional red barn with white trim, but regardless of color you should paint the barn at least every three to four years for proper protection. This also gives you a regular schedule for making routine repairs and cleaning up unsunk nails, or other possible hazards.
Step 1 - Pick the Paint
Lead is no longer used in the manufacturing of paint. For barn paint, this means that oil-based paints may not handle the elements as well as it did a few decades ago. For longer lasting, sharper color and protection, most experts today recommend using acrylic paints. Acrylic paint won't fade as quickly as oil-based paints, and when dried they have a tougher finish that is more resistant to scratching and staining.
Step 2 - Prep the Barn
Inspect the barn for loose nails, hooks or objects that have been hung on the barn but should not be painted, such as the traditional horseshoe over the door. Repair any lumber that is decayed or broken. Pressure wash the entire surface to remove dirt, cobwebs, and loose paint. Use a paint scraper and remove all loose paint flakes. Capture all of this debris onto drop cloths for later disposal. Caulk gaps and check the bead around windows and doors.
A Note About Lead Based Paints
Because lead-based paints were the standard for barn and outdoor use only a few years ago, chances are good that the paint flakes being removed contain at least traces of paint lead. These chips are hazardous to people and livestock, and should be collected and disposed of properly.
Step 3 - Paint the Barn
Starting at any corner, work in one direction around the entire barn. Complete one section at a time, and apply smooth coats. The first coat should be a little heavier than the second coat, but pay attention to even spraying. The second coat should be applied slowly and with a lot of attention to detail. This will be the final coat, and it will be visible for the next several years.
Step 4 - Backroll
Outdoor-grade paint is usually self-priming, but the first coat must be applied uniformly. After a section has been sprayed, use a paint roller and go back over the section to work the paint into the wood. This is called backrolling, and helps seal the wood and provide a solid base for the actual finish coat. Backrolling is not required for the second coat. Backrolling is a very effective method of increasing the paint seal on walls that will not receive a primer coat.
Step 5 - Paint the Trim
Select an appropriate brush width, and hand paint the trim for best results. There are not really any shortcuts for trim painting, except to use slow heavy strokes that deposit paint smoothly. Avoid over-application. After the trim dries, replace the items that decorate or enhance the barn.