Mur vs. cloison
In French, while both mur and cloison translate to wall in English, they are not interchangeable. The key difference lies in their structural function and importance within a building.
Mur
A1A mur is a structural, load-bearing wall. It is a solid, often thick wall that is part of the building's main frame, supporting the weight of floors or the roof. You cannot demolish a mur without compromising the building's structural integrity. It often separates different apartments or major sections of a home.
On ne peut pas abattre ce mur, il est porteur.
(We can't knock down this wall, it's load-bearing.)
Le mur qui sépare notre maison de celle du voisin est en pierre.
(The wall that separates our house from the neighbor's is made of stone.)
J'ai besoin d'une perceuse puissante pour faire un trou dans ce mur en béton.
(I need a powerful drill to make a hole in this concrete wall.)
Il y a des traces d'humidité sur le mur du fond.
(There are damp patches on the back wall.)
Il a accroché une lourde bibliothèque au mur principal du salon.
(He hung a heavy bookcase on the main wall of the living room.)
Cloison
B1A cloison is a partition wall. It is a non-load-bearing, thinner wall whose only purpose is to divide a larger space into smaller rooms. It is typically made of lighter materials like plasterboard (placo), wood, or glass, and can be removed without affecting the building's structure.
Nous allons monter une cloison pour créer une chambre supplémentaire.
(We are going to put up a partition to create an extra bedroom.)
La cloison entre le bureau et le couloir est très fine, on entend tout.
(The partition between the office and the hallway is very thin, you can hear everything.)
L'architecte a prévu une cloison amovible pour moduler l'espace.
(The architect planned for a movable partition to modulate the space.)
Le bureau est très lumineux grâce à sa grande cloison vitrée.
(The office is very bright thanks to its large glass partition.)
Il a suffi d'abattre une cloison pour agrandir le salon.
(All it took was knocking down a partition to enlarge the living room.)
Summary
In essence, think of a mur as a fundamental, structural wall that holds the building up. In contrast, a cloison is simply a divider, a lighter and thinner wall used to organize the interior space that can be changed or removed.