Originally Posted by finskie
Either way in this description, the tarp fails. Whether it is at the sew line, or at the edge of the taped seam. What I am wondering is: Does one of these ways fail under less pressure than the other, or is it just different ways of failing? Was your reason for sewing and then taping just to elliminate the need to seam seal, or to add strength? Just wondering for future purchases.
The amount of stress needed to make a sewn edge fail is less than a taped/sewn, glued/sewn, glued or taped edge. When testing, a sewn edge ALWAYS ripped in the same spot - at the sewn edge. Glue and tape has its own disadvantages, but the sheer strength of glue or tape is considerably stronger than a sewn edge. I taped to add strength. My tarp was version 1.5. The first tarp (1.0) was used as a test subject to test all the different methods of attaching tie-outs, with each tie-out using a different glue/tape/sewn combination. I will say that none of the methods used has failed on version 1.0, and that tarp's tie-outs and ridgeline are bomb-proof. The stress on a tarp is mostly on those points. Version 1.5 was done with sewing and tape on the ridgeline only, all the other attachments were glue/tape, except for the grosgrain tie-outs, which were sewn through several layers of cuben, then adhered to the main tarp. The ridgeline was sewn and taped to strengthen the bond and
to seam seal. It was only done because I was on a very tight schedule to get on the trail, and I had concerns on the adhesion peel strength of glue and/or tape, which after more thought isn't really a factor on a ridgeline. If I could do it again, I would only glue or tape the ridgeline because it would save time and not introduce weaknesses in the fabric that would need to be re-bonded through the use of tape.
There was a lot of research and reading done on the subject of bonding cuben, sheer strength and peel strength before a cuben tarp was attempted - it costs too much to fail just for fun. When you glue or tape cuben, you are basically bonding the polyester film surface that is used to encapsulate the dyneema strands. There is no way to make a seam that is stronger than the material itself because of this. Cuben will
tear, and if you induce a hole in the fabric by sewing, it creates a flaw in the fabric that can be exploited by stress. You are definitely creating a weakness in the film surface and possibly damaging the dyneema strands, although that is unlikely. But you are creating a place for the film to start its tear. The amount of strength needed to start that process is more stress than anyone will probably ever put on their tarp, but it is still the weakest point, and the weakest way to join two pieces of cuben based on people a lot smarter than me with a lot of fancy equipment and big words to throw around.
On the question of whether a cuben tarp needs to have finished edges: Not really, it is done to make it clean and pretty.
Cuben doesn't fray like silnylon. I seriously debated whether or not to do it, but it just makes it cleaner. The edges of my tarp were sewn - just because the amount of force along the edge of the tarp will never reach the failure point of that method. Tie-outs and ridgelines, I have probably put them to greater stress than I ever put a silnylon tarp to. I saw Brian's (OES) prototype cuben tarp at Trail Day's, and he also stayed away from sewing. BTW, he is a great guy in person, glad to have finally met him. Hyperlight Mountain Gear, Mountain Laurel Designs, HammockGear with Adam's new tarps - all use tapes and/or glues to bond their cuben tarps with little or no sewing, and if they sew, only where it is cosmetic and not critical. That alone says something, doesn't it?
Have fun, guys! I have to get my new hammock done so I can get back on the trail!