I found this blogg when looking for a fix for a thrown away rian butt I am trying to resurrect. After reading the responses I have come up with my own solutions, albeit informed by others on this bb.
This involved the following: detergent and a scrub brush, a small blow torch, glue gun stick, two strips (each the length of the crack plus about 4 inches (100mm)) of foil tape (i think this is for roofing work) and is 3 inch (75mm) wide foil with backing paper, a quarter inch (6mm) drill bit and drill, and 7/8th inch (22mm) selant strip for bathrooms and kitchens, the same length as the foil tape above.
First drill quarter inch (6mm) holes on each end of the crack, to discourage the crack extending itself. Then scrub clean the crack on both sides and at least two inches (50mm) around it , inside and out. Rinse well. Position the crack on the outside to being at the top of the butt, when lying on ots side. Use the blow torch to dry and heat up the crack area, until the surface just begins to blister. Mlet the glue gun stick with the blow torch and drip it into the crack, l,etting it flow in by gravity. Apply one of the lengths of foil tape over melted glue, with thew crack in the centre, and press the tape down to press the melted glue into the crack and seal the area around it. Turn the butt so that you can reach inside and the crack is now at the bottom. Repeat the action with the blow torch on this side, slightly blistering the surface, applying melted glue, but this time apply the sealant strip. after removing its backing. Press this tight into place, again forcing the melted gluer into the crack. Finally apply the last piece of foil tape over the sealant strip, pressing it ouit to best cover the repair area.
A final touch is to wrap duct tape around the whole butt at the level of the crack to stop any bulging in this area which might weaken the repair.
I just tried this all out, and, at least initially, it seems to work.
Michael Rosenbaum