What is the material of the sliding door crib? It is compact, not too wide and does not take up space.

Just use a brick. Why must it be square? It just has to be built to the top; And there will be a lintel connection above the door (height), so there should be no problem.

When laying, the cement mortar label should be higher (for example, 1: 2 ~ 3), which will improve the firmness of the plug.

In addition, 75mm light steel keel can also be used as partition wall, and cement board+steel mesh+cement mortar can be sealed twice. In this way, its thickness should be about 13 cm, and it is also possible to stick tiles on it.