An ostomy body side mounting wafer and a method of preparing the ostomy body side mounting wafer, where the wafer is assembled from two parts using laser welding. The laser light is provided through one of the parts having a low or lower absorption of the laser light. The other part has a higher absorption of the laser light, whereby the interface between the two parts is heated at the welding zone(s) of the laser light. In this manner, an assembly is obtained independently of the thicknesses of the materials and even close to openings or other edges.