This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Plaster Grounds. Where any woodwork is to be applied against a plastered wall, such as a baseboard, chair rail, wainscot, picture molding, etc., it is always necessary to provide a proper bearing to nail it against, in order to avoid cracked plaster and insecure fastening, which would result from nailing through to the lath and plaster into the stud. Therefore, a ground, or nailing strip a, Fig. 73, is nailed against the studding at such a height as the top of the base, or other trim, will reach, and of a thickness equal to that of the lath and plaster. To this ground the trim is fastened when the plastering is finished and dry. When the trim to be applied is in the form of a wainscot or other wide surface, it is sometimes necessary to have several grounds at different heights, to which the separate pieces may be attached. It is always desirable in first-class work to have the walls lathed below the grounds, even down to the floor line, and also plastered to that point, as the back of the trim is thereby protected from exterior dampness and drafts, and vermin have less opportunity to make passages behind the walls.
124. Though the primary purpose of grounds is to form suitable nailing places for interior trim, they, at the same time, exercise another and most important function - that of forming a stop for the plaster. If no grounds are provided, and the plaster is simply carried to some arbitrary point which will be hidden behind the trim, we have an insecure job, the edges of which are liable to break off and crack as the trim is put in place, thereby necessitating patching and repairing after the job is complete; but if a ground is placed at every side where the plaster will stop, the entire wall surface is enclosed in a frame, and is secure from damage.
125. When lathing is applied to the ceiling of a room, it is sometimes nailed directly to the under side of the ceiling beams, though in first-class jobs it is always best to provide some means of bringing the bottoms of the ceiling beams to a level alinement before the lath is nailed on.
Cross-Furring. In Art. 108 is explained the method employed to bring the top of all the floorbeams into alinement, and, as will be readily seen, any irregularity in the depths of the beams will, by this method, be thrown to the under side. Therefore, when the under side of these beams is to carry a plastered ceiling, they must first be leveled by a system of cross-furring. This is accomplished by nailing thereon furring strips 1 inch thick by 2 inches wide, and spacing them 12 inches on centers. These furring strips are either notched over the beams or dropped below them by the insertion of slips to bring them in line.
On these furring strips the laths are then nailed, and if, on any side of the room, there is no beam in the angle between the side wall and the ceiling to which a furring strip can be nailed to secure a firm corner, pieces must be nailed on the plate of the partition to receive the ends of the strips, in the same manner as nailing places were established at e c and e d, in Figs. 37 and 38, to receive the ends of the lath. When a ceiling is cross-furred, it is more rigid; the plaster is less liable to crack by the vibration of the floor-beams, and, being generally of less width than the thickness of the joists, a better rivet is secured for the plaster.
127. Trussed partitions are sometimes necessary where there is no supporting partition in the story below, or where a partition has a number of doors or other openings through it so weakening it that it cannot safely carry the required weight to be imposed upon it. Fig. 39 shows a trussed partition with a door 4 ft. 6 in. x 7 ft. 6 in. in the center of it. The sill a and the plate b are made 5 in. X 7 in. The studs c at each side of the door are 3 in. X 5 in., and the upright wall members g are 6 in. x 5 in. The height of the door is limited by the 3" x 5" timber e, from the ends of which the 4" x 5" braces d extend to the ends of the sill a, where they are let in at j, to secure them from slipping. A truss cqpr is thereby framed, around the members of which the 2"x5" studs fare cut. The entire weight of this partition, together with any superimposed load, will come upon the points c and r, where ample support must be provided to carry the weight down to a proper foundation.
128. In Fig. 40 we have a partition with three openings, the essential difference between it and that shown in Fig. 39
being that the truss is entirely above the openings, while in the former example the opening was through the center of the truss. In Fig. 40 we have the sill a, into which are mortised the wall members g. The tie-beam f marks the top of the openings, and into it the rafters, or struts, dare notched at each end, with the compression member e between their tops. This entire truss km In is carried by the wall posts g, and the weight of the door posts and the studs between them is carried to the top of the truss through the tie-rods i, which pass, also, through the plate h; the weight of the entire partition is therefore carried by the corner, or wall posts g, which, in turn, must be well supported from below.
129. Door and window openings more than 3 feet wide, should have their heads trussed, as in Fig. 41, the tie-beam c resting upon the studs d, and the struts e footed into the tie-beam. This prevents the top of the door from sagging in the center, as the superimposed load is all carried to the side studs d.
Double studs, or larger sized studs, should, therefore, always form the sides of door and window openings, as shown at d, Figs. 41, 42, and 43, for the purpose of gaining strength and also to afford a nailing place for the trim. When a single piece of timber of the proper size for this is not at hand, it is.customary to spike together two pieces of the ordinary studding and use them as a double stud, as shown at d, Fig. 42.
130, The sizes of doors and windows as marked on plans or working drawings are the dimensions of the finished parts, and in framing the openings for them in the studding, an allowance must be made for windows of about 5 inches in height and 7 inches in width, where there are weights; but if the window is to be hung without weights, an allowance of 3 inches at the sides will be sufficient.
In door openings, false jambs are generally inserted, as shown at c, Fig. 43. These are nailed to the studs, and the plaster finished to them, in order to make the sides of the opening perfectly vertical and the top level; therefore, an allowance of about 5 inches in width, and 3 inches in height is required in framing the stud openings for doors, and an ordinary door, 2 ft. 10 in. x 7 ft., would require a framed opening 3 ft. 3 in. X 7 ft. 3 in. When setting the finished jamb, solid blocks should be placed where the hinges of the door will come, as shown in Fig. 43.