Many homeowners are disappointed with the results of natural weathering of their wood sided houses. Often the wood has bleached areas in some spots, darkened areas in others, with the remainder somewhat in between. Rain and sunlight both affect weathering.
For example, if sunlight remains on one portion of the house for long periods each day and never hits other portions, the color will be different. If rain splashes on the lower portion of the siding, it will have a different color from the remainder. Areas near roof valleys or places where rain water runs off a roof are usually darkened because of the excess additional water that hits these areas. If you like "pure natural weathering," this is it.
To keep some uniformity of color, many homeowners put on a clear water-repellent preservative. This would also lengthen the life of the siding by protecting it from decay. The wood may be slightly darkened from its original color, but in most cases this is unnoticeable. Tints of many shades can be added to give the desired appearance, including the silvery gray look that so many people want. Mildew is a major problem in the southeastern United States. It causes many of the dark blotches that are so unsightly. Water-repellent preservatives will minimize this problem.
"Natural" may be good, but most often it is not what most homeowners really want in weathering of wood siding. Take measures to prevent these problems. In many cases, if you wait until the wood has gotten a blotchy appearance, you won't be able to restore it to its original beauty.