Abstract: An insulating material plate (4) is fixed to the surface (6) of a structure (8) by a dowel (2) with a disk-like head (14), countersunk in a countersunk hole (24) of plate (4) and carrying on its outer surface an insulating material washer (10). Washer (10) prevents the thin plaster layer (22) from separating at the location of dowel head (14), due to the thermal expansions and differing thermal conduction between the dowel material and the mortar material. The insulating material washer (10), which is e.g. made from the same material as the insulating plate, also makes it possible to level the outer surface (20) of the insulating material plate by abrasion, prior to the application of the mortar layer, so that a smaller thickness of the latter can be used.