A system for mounting wall panels to a wall includes wall panels, each including a main wall panel section, and four bent end sections extending from edges of the main wall panel section; a plurality of main fastening extrusions, each including a base secured to the wall, two spaced apart post walls extending from the base section, and two bent end securing walls extending from the base on opposite sides of each post wall, with a spacing between each post wall and an adjacent bent end securing wall being equal to the wall thickness of one bent end section; and a recess at a first surface of each bent end section which faces a second surface of a respective bent end securing wall, and a projection at the second surface of each bent end securing wall which is adapted to be received in a respective recess.