What did the ancient architecture originally refer to as two sides and three knives?

1. This is an architectural term in ancient architecture and a standard of bricklayer's technical level. The original meaning of duplicity refers to the basic skills and actions of bricklayers when building walls. In ancient times, there was no cement for building walls, and the wall bonding materials were mostly yellow mud with good viscosity, and there was a little precision engineering gypsum (that is, adding a proper amount of lime slurry to the yellow mud), which required high production and good viscosity. Almost all the broken bricks are made of small green bricks (or broken bricks), and the walls made of bricks are generally drywall (referring to the outer wall). When bricklaying, tile knives are used as joints, and the mortar joints are thin. Double-dealing includes double-dealing. Two sides refer to the two joint surfaces of a brick, generally referring to the lower surface and the top surface or side surface. When the bricklayer picks up a brick with his left hand, the brick will rotate and turn over quickly in his palm at the same time, so as to observe the shape of the brick and determine two suitable bonding surfaces. Three knives means that when laying bricks, the tile knife digs a little mud from the mortar bucket and batches the bonding surface of bricks in three times, that is, two gray ridges are bonded on the front and one gray ridge is bonded on the top or side. Brick walls built by skilled masons are smooth and beautiful. However, the master with poor technology either chose the two joint surfaces badly, or the amount of mortar dug on the tile knife was more or less. When the mortar ridge is approved, it is not three knives, but four knives or even five knives before it is finalized. In ancient times, the cultivation of apprentices and bricklayers also started from two sides. When climbing the wall, the master deliberately put the apprentice between the masters with better skills and spread it on the same wall, in order to force him to pay attention to quality and speed up. The apprentice was sweating like a pig, and his back ached, and at the same time, his skills also went to a new level. 2. However, it finally evolved into a derogatory term for people. Cao Xueqin's Sixty-fifth Story of A Dream of Red Mansions: sweet words and painstaking efforts, two sides and three knives; He smiled and stumbled; Ming is a pot of fire, and darkness is a knife, which accounts for all. Metaphor is insidious and cunning, playing with two-faced tactics and provoking right and wrong.