weld on #16 will work fine, but you must apply it correctly
using a natural hair fine point paint brush (look at arts and crafts store for the smallest cheapest natural hair brush), you must apply a thin layer of #16 to each side of a joint and then quickly clamp the pieces together
if you want to weld a joint that you already have taped together, you need Weld on #3 or weld on #4 ... set your joint with tape, apply the adhesive to the joint and then clamp tightly together, come back in 30 min and repeat 2 or 3 times for max strenght.
also, if you have a 90 degree joint and you bend the pieces away from each other, you're placing a LOT of pressure on that very small joint - I doubt any adhesive would hold it. but if you glue two pieces together end to end, and then try to pull them apart - good luck