Whether you're installing rough-cut lumber on the outside of your home or using it for shelves inside, you can paint the wood yourself to help seal it from spills or outside elements. Rough-cut lumber is often more difficult to paint than traditional, smooth lumber because of the roughness and depth of the wood grain. Special treatment and steps should also be taken before painting rough lumber to remove any dust or debris stuck between the grain or grooves in the board.
Stand your pieces of rough lumber up against an exterior wall.
Mist both sides of the wood with a spray of water. You want the surface of the wood to be damp. Do not soak the wood.
Mix a sodium hydroxide-based cleaner at half strength. Use the manufacturer's instructions as a guideline. If the manufacturer's instructions say to use a 1/2-cup of cleaner per 5 gallons of water, use half of the amount of cleaner specified in the suggested amount of water. In this case, half of a 1/2-cup is 1/4-cup.
Put the cleaning mixture in a pressure washer. Use the pressure washer to clean the boards. Work slowly and carefully to make sure you do not damage the boards.
Let the rough cut lumber dry completely. This typically takes two or more days.
Use a thick-napped, 3/4 to 1 1/2-inch roller to apply an even coat of latex primer to the surface of the board once it's completely dry. Let the paint dry overnight.
Apply an even coat or two of latex paint in your desired color on the surface of the lumber using a second thick-napped roller. Leave the paint to dry completely.