Abstract: A method and apparatus for heat-welding corners lengths of profiles together, for sealing gaskets, where the profiles include at least one extendible or compressible air chamber and are cut at their ends at an angle. The method includes positioning two profiles, with one of the cut ends of each profile opposite each other inside a suitable device including clamps which make the positioning possible, heating the positioned ends until the positioned ends reach a softened state, choking the profiles so as to completely occlude the air chambers along choking sections, closing the clamps in order to cause the profiles to come into mutual mating contact at the heated ends, injecting air into the air chambers by perforating the air chambers in a region between the choking sections and the heated ends so as to apply pressure to walls of the profiles in that region, pressing the walls against walls of the clamps to join the heated ends by heat-welding under pressure, and opening the occluded sections.