These are usually narrow strips nailed to the walls, furring or studding, around openings to stop the plastering, and also to form a guide for the workman. They are also placed behind baseboards, wainscoting, etc. The position of the ground around the windows is shown in many of the window frame details, Chapter III (Layout Of Trussed Roofs - Bracing Of The Roof And Trusses)., by the piece marked G, and around door frames by the same letter in Fig. 234 ; in Figs. 120-122 it is indicated by diagonal lines. Grounds should always be set so that their face will be flush with the plastering and back ½ inch from the outer edge of the finish (so that the, latter will lap that much on to the plaster), and should be perfectly straight and plumb. As the plasterer is supposed to bring the plastering to the face of the grounds, if the grounds are not straight or plumb the plastering will not be. It is also obvious that the thickness of the grounds regulates the thickness of the plaster. Where the plastering is applied to wooden laths the grounds should be \ inch thick for two-coat work, and \ inch for three-coat work. Where the plastering is applied directly to brickwork or tiling, 5/8-inch grounds are generally-used, and also for most of the metal laths. The thickness of the grounds should be given in the specifications ; the usual width of the grounds is about 1 ¼ inches.
For first-class work grounds should be put behind the base, chair rail, wooden cornices and all inside finish to insure that the plastering will be straight. On brick walls grounds also afford a nailing for the wood finish. When the window and door "trim" or casings is made up of several members it is often necessary to put on wide grounds to form a back for the finish. The ground behind the base should be put so as to receive the upper edge of the base and the bottom of the base mouldings, as in Figs. 234 and 269, and it is also desirable to have another ground at the bottom.
In a great many cheaply built buildings the grounds are entirely omitted, except where necessary to form nailings for the wainscoting, the plastering being simply brought to the edge of the door and window frames and carried to the floor, without much regard as to whether it is straight or not. The result of this kind of work is that when the finish is put up the plastering is found to make a wave line behind it, and the irregularity is frequently so great as to cause the finish to be in "wind." The only practical way in which the finish can be made to fit nicely against the plastering is by the use of grounds, and they should always be specified. The woods commonly used for grounds are spruce and the cheaper grades of white pine.