Cedar is a very durable wood, but its surface characteristics are quickly changed by the actions of sunlight and water, especially in harsh climates. Although cedar is resistant to rot, it is not immune to it. Sections of cedar siding that are prone to rotting are unprotected end-grain areas and pieces of siding near or touching the ground.
Cedar siding should be coated with a finish that provides water repellency and protection from ultraviolet light.
The finish should also contain a wood preservative that kills mold and mildew. Ideally, the finish should allow the wood's grain to show through. For this reason, penetrating oil-based semitransparent stain is a popular choice. It is lightly pigmented and provides water repellency. The pigments in the stain provide a small amount of protection from the damaging effects of ultraviolet light. Solid color stain or paint is also a popular option which often lasts several more years than stain.
There are high quality products available, life expectancy of stains can be short lived. Recommend consultation with an expert in the field of paint sealants.
Clean the siding and let it dry before applying two coats of the stain. Surface cleaning may be done with low-pressure power washing using a detergent and mold removal cleaner.
Monitor the cedar siding for peeling paint, cupping or warping , which is more of a problem on the southern exposure side of the building.