The angle of yin and yang should be made into an arc. (4) the thickness and strength of the protective layer cement mortar ... The brick with internal angle should be pressed, and the external angle line should be docked at a 45 angle, protruding from the wall ... Polished with fine sandpaper, after removing scratches and residual impurities, the wall can be pasted only after it is flat, dry and the internal and external angles are clear.