A Timber Pile is used to dry boards for more demanding building projects. The Pile needs to be placed well away from other objects to reduce the risk of mold growth.
As stated by TM: Players, animals, and foragables have no effect on board piles. Only actual Structures that also have Hit Boxes, which means that leantos are also fine, but things like toolboxes, walls, and smelters are not. Natural structures count too so don't put board piles next to growing trees or whatever. Cliffs do not hurt your board piles.
Follow the illustration below to increase your chances of avoiding moldy boards. No structures of any kind should be present within 5 tiles of the timber pile. Farms and paving do not cause mold. All other structures should be avoided. Great care must be taken to ensure that even other timber piles are not within close proximity to one another because even on perfectly cleared terrain, piles have a chance of becoming moldy. If that happens, mold then has a chance to spread to any nearby timber piles as well.