Treating and painting softwood
Softwood used outdoors is either pressure treated at the mill or coated on site, and most small buildings are both. Pressure treatment protects the timber that was in the tank; it does not protect the face a saw has just exposed. Cutting a treated board leaves untreated end grain, and end grain absorbs many times more water than a face does.
The practical consequence is that cut ends are coated with an end grain preservative as they are cut, on the bench, before the piece goes into the building. Once the board is fixed, the end that mattered most is usually the one buried against a corner post or sitting on a sill where no brush will ever reach.
On the face, a penetrating stain and a film-forming paint behave differently as they age. A stain fades and is recoated by washing down and applying more. A film cracks, lets water behind it, and then has to be stripped back before it can be renewed. Neither is wrong, but the choice commits the building to a different kind of maintenance for the rest of its life.
Coatings go on dry timber, in dry weather, with time to cure before rain. Two thin coats outperform one thick one, and the bottom edges of boards, the undersides of sills and the backs of battens are the surfaces most often skipped and most often the first to go.
Two coats drawn on end grain
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