Split cover boards are used for heavy books with several signatures so that the construction remains solid and an adequate level of support can be provided. Figure 200 shows a split board that comprises of a mull and the endsheet placed in between a thick and thin piece of board. These board layers are used for stiffening purposes and conceal the mull and the endsheets between them.
Cut four pieces of boards that are equal in size; two of them should be thin, and the other two should be thick. Apply some paste onto the mull; place tapes over it, and apply paste onto them as well as shown in figure 201. Fold the taped up mull onto the endsheet, and press it firmly as shown in figure 202.
Trim the top edge of the endsheet by one fourth of an inch, and put some paste onto it. Fold the endsheet over itself as illustrated in figure 203 such that its edge is at a distance of one fourth of an inch from the hinge. Rub the endsheet and remove all air bubbles. Turn this flap across the edge, and apply paste onto it as shown in figure 204. Place the thin cover board onto the signatures as shown in figure 205, and paste the turned over flap onto it as depicted in figure 206. Attach the thick board onto this as shown in figure 207, and ensure the edges are smooth and aligned. Leave your work for about twelve hours; when it dries up, rub sandpaper on the edges.
Your book now will not be damaged easily because it is protected by a really strong binding form.