WOOD FORMS.
Wood for forms must be of a kind that is easily worked and that will retain its shape when exposed to the weather. White pine is the best wood, but is seldom used because of its cost. Spruce, yellow pine, and fir are satisfactory woods for forms and are best, used partially green or unseasoned.
The edges of boards should be surfaced, tongued and, grooved, or beveled in order to obtain a tight form, so that the soft mortar will not ooze out. A better surface* is secured if the boards are dressed on one side and are free of loose knots or other imperfections.
As forms must be removed, they should be so planned that they can be taken down without destroying the lumber, especially if the boards are used for sheathing or again for forms. Therefore the nailing of the boards to the support should be only sufficient to keep them in place until the concrete has hardened. Greasing the surface next to the concrete with crude oil, soap solution, or linseed oil will prevent the concrete from adhering and facilitate removal.