Wood slab furniture is exposed to rain, snow and blazing sun. Paint the furniture with some old paint will not give you a good long finish. Regular paint does not expand and contract with the wood and can flake and chip with exposure to moisture and heat. Oil-based enamel paints work well for outdoor furniture, maintaining its surface through the seasons. You will need to reapply color every five to seven years to keep it looking great.
Mix two tablespoons of dishwashing liquid with one gallon or more of warm water. Dip a scrub brush in the mixture and scrub the furniture to remove the dirt. Rinse with clean water. Set the furniture in the sun to dry. Sand the surface with medium sandpaper. Sand sufficient to create a rough texture without having to clean wood. Wipe away the sanding dust with a tack cloth.
The chamber a small amount of wood putty on a putty knife. Fill any cracks in the wood slab furniture with putty. Overfill slightly. Let the putty dry. Sand the surface of the crack until it is level with the rest of the surface. Coat the surface with oil-based primer. Has paint store tint the primer to coordinate with the color you will use. Apply a thin layer of primer with a brush. Let the first coat dry. Apply a second coat of primer. Let the primer dry overnight.
Paint the wood slab furniture with oil-based enamel paint. Apply a very thin layer of paint with a brush. Let the first coat dry to the touch. Apply one or two additional coats of paint. Allow the paint to cure for 48 hours.