Abstract: A method for fabrication of an integral shell-formed body from several elongated panels (1, 2, 3), each of which along one longitudinal edge has a substantially U-formed tongue groove (6) and along the opposite longitudinal edge a tongue element (8) which is at least partly substantially narrower than the groove (6) thereby providing a clamp groove (12) when the tongue (8) is introduced in the tongue groove (6). One or more clamp blocks (13) can be introduced into the tongue groove to press the tongue (8) sideways and preferably also to the bottom of the groove (6). Preferably a layer of settable glue is provided between the groove (6) and the tongue (8), which glue layer is allowed to set after the groove and tongue elements have been clamped together by the clamp blocks (13). The clamp blocks can be formed as G-clips embracing and engaging the groove-tongue joint.