How to Protect Wood Siding
To prevent rot and prolong the life of your wood siding, you can treat it with oil, stain, or paint. These materials act as a barrier, preventing water from coming into direct contact with the wood. Which finish you choose is mostly an aesthetic choice:
Oil, a clear finish, is absorbed into the wood, filling all pores and voids, thereby displacing water that otherwise would be absorbed.
Oil stain is the same as oil except that a pigment is mixed into the oil.
Paint penetrates and protects in the same way that oil does. Additionally, paint coats the surface of the wood with a thin, durable, waterproof hide.
Oil is easier to apply than paint is, and if the oil is clear (or almost clear), mistakes are nearly impossible to detect. If the oil contains stain, the added pigment makes application slightly more difficult, as mistakes show up more readily. But the added pigment helps filter out more of the sun's damaging ultraviolet rays. Unfortunately, oil has a tendency to evaporate and doesn't last as long as paint. However, unlike paint, oil and oil stain don't split, chip, or blister.
Everything's a trade-off. With oil, you never have to sand, scrape, or chisel the surface to prepare it for another application. But be ready to apply a new coat every several years. With an oil stain, expect three to five years of lasting quality. A good grade of paint, applied to a properly cleaned surface, lasts seven to ten years or more.
Prepare for repainting by ensuring that all old loose paint has been removed. A new coat of paint won't stick any better than the old paint below it.
Whether you hand scrape or pressure wash, be sure to sand spots where a painted surface meets a bare spot. Feathering these transition points makes them less visible and guarantees a nicer-looking finished product.
Prime all bare spots with a high-grade oil-based primer. Then caulk all joints with a high-grade 50-year, paintable silicone or polyurethane product to prevent water from getting behind the siding. Caulk any joint that allows this to happen.
Tinting a standard white primer a shade or two lighter than the finish coat improves coverage. For example, a light brown finish coat covers a beige primer more effectively than it covers a white primer.
With an oiled surface, clean the wood with a pressure washer, apply a coat of wood bleach, let it stand (per the manufacturer's instructions), and pressure wash again. At this point, you can apply a fresh coat of oil or oil stain. Your oiled siding will look so good that you won't believe you did it yourself.