Abstract: The frame shim comprises a first and a second elongated plate made of a porous material, which plates are located in planes extending parallel to each other and which are connected to each other along their longitudinal sides. A groove is formed in one longitudinal side of one of the plates, and a laterally located ridge is formed in a longitudinal side of the other plate, which ridge is set into the groove. The other longitudinal side of the laterally offset plate is strengthened and the door fittings are mounted to this longitudinal side. The legs of the groove are also strengthened. This allows the manufacture of the frame shim of a door from a plate made of a porous material.