When reapplying solid-color stain, wash the surface to remove dirt and mold. If areas have peeled exposing the wood surface, the weathered surface must be removed prior to re-priming the peeled area. The photo shows an extreme case of surface degradation following the failure of the coating. Solid-color stains form films, and like all other film-forming finishes, do not bond properly to weathered wood. It has been well established through several studies that cedar exposed to sunlight for as little as 2 to 3 weeks will not hold film-forming finishes as well as an unweathered surface. It may be possible to remove the damaged wood from small areas by scuff sanding, but this is difficult with shakes and shingles because the surfaces are saw-textured or split. The sanded surface won’t match the unsanded surface. If the previous finish contained lead, do not sand.
The situation shown in the photo is an extremely difficult problem to reconcile. A penetrating finish, such as an oil-based semitransparent stain, cannot be used over the existing finish, and a film-forming finish will not adhere to the weathered surface. It is probably necessary to remove all the finish and the weathered surface by power washing prior to application of the primer and solid-color stain. This may be one of the few instances where careful power washing by a skilled operator is necessary. As with using a garden hose to wash siding, keep the nozzle pointed down to avoid forcing water behind the siding. Paints refinish in the same way as solid-color stains. Lap marks should not be a problem with paint systems.
Careful and judicious work will yield good results for the homeowner.