Generally there are several reasons :(a) the expansion coefficient of the substrate is larger; (2) There is displacement or vibration; (three) some domestic glue itself is too thin, the filling material in the glue is less and more plasticizer (white oil), the plasticizer (white oil) in the curing process has a certain degree of volatilization makes the volume of the glue smaller, so the glue will shrink and wrinkle; (4) If the sizing is too thin after curing, it is easy to shrink and wrinkle, and the thickness of the thickening sizing can reduce the occurrence of this phenomenon (it is recommended that the sizing is more than 2mm).