Abstract: A method for forming a leak free container, such as a paper cup, including a sidwall having a lap joint and a bottom wall connected to the sidewall by means of a bottom wall lap joint incorporating a portion of the sidewall lap joint wherein the method includes the step of applying caulking material, at a predetermined location, to one of the blanks forming the bottom and sidewall which location is selected to insure sealing of any void volume formed adjacent the sidewall lap joint within the bottom wall lap joint. Preferably, the caulking material will be a hot melt adhesive and will be employed in a cup making process involving the use of polyethylene coated paper stock. Careful control of the temperature, amount, location and viscosity of the hot melt during the lap joint forming process and of the heat and temperature used in the lap joint forming steps insure that the hot melt material ends up residing in precisely the appropriate location within the void volume.