Strength of .93 oz Membrane Silpoly vs 1.24 oz Silnylon

[Mario Caceres]

Hoosier, did you glue the reinforcement patches before sewing?.  It also helps when you seam seal the stitches. (makes them stronger).

[Hoosier T]

Yes, I did glue them. Unfortunately, I haven’t yet had a chance to seam seal. I don’t think glue vs only stitching would make a difference here since its at the step down from the reinforcement to the panel. Any advice or is this pretty much trashed?

[Mole J]

Nuts.  Not sure what you can do here. Others may advise.

Thoughts for the next Tarp (based on own observations of manufactured UL tents and making own silnylon tarps). Others may differ. I have not tried such  a UL fabric for a Tarp.

I’ve used wider hems and much of the tieout stitched to these.

Reinforcement patches to be a little larger and curved on the inner edges (I.e. Semi circles on edges and quarter circles at corners.

If glued, then stitched later. Not tried glueing,  as my fabrics seem strong enough so far. My Trekkertent had glued patches on silpoly.

Patches of same material as Tarp so stretch is similar. (if a heavier different fabric has vastly less stretch than Tarp fabric, surely it will concentrate force at the stitch line? Don’t understand why stiffer fabrics used for stretched reinforcement?)

 

Good learning.  You can make a slightly narrower /shorter Tarp if it fails?!

[Hoosier T]

I’ve used wider hems and much of the tieout stitched to these.

In my pictures you’ll notice that the tie out loop is sewn entirely to the hem. They’re 1/2″ hems.

Patches of same material as Tarp so stretch is similar. (if a heavier different fabric has vastly less stretch than Tarp fabric, surely it will concentrate force at the stitch line? Don’t understand why stiffer fabrics used for stretched reinforcement?)

Being my first tarp, I just tried to research and compile all my findings for a strong setup. Since RSBTR includes HyperD300 for their tarp kits I assumed it was suitable since both it and the tarp itself are polyester.

I’m really frustrated as I still feel that I got most of the details right…stitch length at 8 per inch, patches glues then sewn, etc. The thing is, none of the reinforcement detail really matter at the end of the day because it’s ripping at the step down. The rest of the tie out are is rock solid. Where the ribbon is sewn on, the actual hem, all is holding up REALLY well. It’s only the area within the red circles that’s stretching out the fabric where it steps down from the reinforcement patch, the highlighted areas are rock solid and are not stretching at all so I’m just lost here. Maybe the force needed to get a flat tarp’s ridgeline taught is too much for this stuff and it should only be used for cat cuts, I don’t know…

 

 

[jh]

I made a tarp out of the first generation silpoly and the same thing happened at the point where I attached grosgrain to the hem and box-stitched it. I am not sure if the superlight polyester fabrics are durable enough for long term backpacking use.

However, there are many examples of completed silpoly tarps on HammockForums and little evidence of failures.

[Hoosier T]

Yea it’s a bummer because I spent the time to make this so I could save some cost as I wanted to end up with two tarps, a nice big open flat tarp for nice, warm weather and then I was going to pick up a second tarp, likely a Cirriform (just posted a WTB for a Cirriform due to this issue), for crappy weather. Two options was gonna be awesome but now that I’m going to have to trash this I’m likely just going to end up with the one shaped tarp which is a drag for summer. Live and learn I suppose…

[jh]

 

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[Hoosier T]

Yea, for a shaped tarp I have no desire to get anything other than the Cirriform. It’s a beautiful design and looks to be very weather-worthy. I have an email out to Gen to see how quickly he can get me a Sil 2p Cirriform tarp. I have a trip next weekend so this little ordeal has me in a bad spot as I sold my Copper Spur to fund this shelter adventure I’m on.

[jh]

 

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[Jennifer Mitol]

Just a quick question from someone working on my own shelter with this stuff – should these high stress points have 2 lines of stitching or just the one?  Would that matter in this situation?

[Hoosier T]

I don’t think it would matter how many lines of stitching you have. The outermost line where the fabric steps down to the single layer of Membrane is where it’s failing. My inner triangle stitch on the interior of the reinforcement is holding up very well as are all of the highlighted areas. Only the red circled areas are failing. In my opinion, based on my results, you can add as many stitches to the interior of the patch as you want but at some point it has to step down and it will fail there regardless since the stress of that last line still depends on the strength of a single layer of membrane.

[Jerry Adams]

If the reinforcing fabric doesn’t stretch as much, it will carry all the load, so only the row of stitches on the edge will carry any load.

Better to use the same fabric as the tent, then it should better share the load.  Then, I usually two two rows of stitches, for one thing I might not be the most expert sewer with best machine and thread.  Another thing is, for the first row of stitches, I’m carefully positioning the reinforcing piece so the stitches can be a bit un-even.  For the 2nd row of stitches, I just sew at a steady speed all the way along, so maybe a little stronger.

Maybe you could cut a piece of the tent fabric, slightly larger, and glue it on.  On the side opposite the reinforcing patch.  Go 1/2 inch beyond the row of stitches that’s failing.  That should enable you to use that for a long time.  First do test pieces to get the formula down.  See that other thread.  Maybe set up tarp first to get fabric under tension, but just a little, don’t really stretch it out.

 

[Hoosier T]

Good call Jerry! I have some extra membrane so I’m going to try that tonight. I’ll concentrate some extra silicone on the stitching too before I lay the patch down. Back to the grind…

[Jerry Adams]

When you’re making a prototype (intentionally or not) you want to get every bit of information you can after an iteration before making the next prototype.  If you can save one iteration of prototype, it saves a lot of work and money.

Like, you’ve determined the reinforcement needs to be modified.  Also, actually use it on a trip to see reality.  Maybe you’ll find some other defect.

Even better is to calculate theoretically rather than actually having to build a prototype.

[J-L]

Part of the reason it’s failing there is because of the heavy reinforcement fabric used. The heavier fabric is not going to stretch much at all, so the tie-out itself will appear rock solid. But all that stress will be transferred to the one row of stitching along the membrane fabric (as already mentioned above).

Hoosier, since you already have the tarp mostly built, you could try cutting off a few inches from the ends and sewing or bonding on new tie-outs using 1-2 layers of membrane as the reinforcement fabric. This might help with the thread-hole elongation. For corner tie-outs, I always use the same material as the tarp to try and match the amount of stretch it has: I sew on one small semi-circle about 2.5” in radius, then another larger semi-circle about 5” in radius

However, between your tarp and the pyramid tarp fail from Nick (KT provided a link on the first page of this thread to a description of the failure), maybe these very lightweight silpoly fabrics are not suitable for reliable shelters, or new construction techniques are required. Despite some of them having high water resistance and an attractive low weight, actual use tells the best story

Edit: seems Jerry already captured these ideas and provided some good input :)

[Hoosier T]

After thinking through the mechanism, I think you’re right. Maybe I need to give Kyle @ RSBTR a heads up to not recommend the D300 for Membrane Silpoly tarps. His kits include this for reinforcement, even if you change the option to Membrane Silpoly, which IS an option in his tarp kits. Granted, I didn’t actually order his tarp kit as I wanted specific quantities of each item but I did use that as my baseline/design. Well that sucks…

[Jerry Adams]

great minds think alike : )

[Hoosier T]

Heard back from Kyle. He agrees with all of you and has seen this a couple other times. He is going to spin off a separate tarp kit that doesn’t use HyperD300. Going to try the suggestions tonight and see if I can salvage this thing.

[jh]

Those are very insightful posts, John and Jerry, and will be useful for anyone planning to make a tarp in the future. Certainly helped me in thinking about my next tarp. :)

 

[Hoosier T]

Quick question, I assume I should use GE Silicone II to glue the extra patch on, right? If so, should I also use that on the threads or should I just use seam sealer?

[Jerry Adams]

I think GE II, Permatex, and Sil Net are all pretty similar.  Probably dilute GE II with mineral spirits, maybe 2 parts mineral spirits to 1 part caulk.  Or 5:1.  Whatever you do, try it first.

Use the same thing to seal seams, maybe thinner for seam sealing.

I think that most seams don’t need to be sealed – won’t leak as is.  You could try using it and seal it if you notice leaks.

[James Marco]

Well, I hate to be the oddball, but the failure might be because of the reinforcements. With all the stretch of light poly fabrics, I believe that tension problems *will* surface exactly as you describe. Again, the strength of the material is rather important, but this is markedly lower at the line of stitches. I have seen many failures like that. It just tears at the last stitch line. Like cuben stuff, it means elongated stitch holes, with eventual failure, at the points of most stress. To reinforce the guy outs, I would simply eliminate the reinforcement patches. The same for any woven cloth where the space between threads is being filled with any solid like material. Even silnylon shows this, though to a lesser degree due to the additional strength.

The reinforcement patches means that there will NOT be as much stretch in that area by about 1/3. (Hmmm, it could be the cube root less but I am too lazy to look it up.) The majority of the stretch MUST be in the panel, itself, NOT on the seams at the panel as it joins the reinforcement. (Not quite true, depending on the elongation characteristics, it might stretch more or less at the initial phases of the pressure…) You are actually better off using a 1/3 lighter fabric for reinforcements than the same fabric, given identical materials. And you want the areas of stitching to be different. You want the force transferred gradually across the whole patch area, not at a single row of stitches. Inside will be about half the size as outside. All will be stitched on the outside of the patch. No Glue. You want each piece to stretch independently to protect the panel.

I believe wrapping the hems an extra roll or two will let you apply a good solid stitch through multiple layers of fabric (4-6 layers of fabric.) Then applying a good seam sealer will lock all the threads and holes pretty much into place. The hems and center seam supply the framework, the patches pick up stress gradually, preserving the integrity of the panel.

I am not really sure you need the reinforcements near the peak. A flat seam rolled a few times withe the hem rolled a few times, then stitch your guy line loops to the center seam and hems.

 

[R]

One more theory to add to the mix:

If a seam is required to transmit a given load, increasing the length of the seam decreases the stress at any given stitch.  If your seam is twice as long, it will see half the force at any given point.

Rather than making the next layer you apply just a half inch bigger on each side, consider making it 2 or 3 inches bigger, or maybe half again (or more) as large as the existing patch. Easier than another round of repairs and it’ll only cost you a couple grams.

 

[Jerry Adams]

So, a row of stitches is like perforating it making it easier to tear?

With Cuben, you’re supposed to glue (or double sided tape) the two layers, then you can sew through the double layer and it will be strong enough

You could do the same with the silpoly – glue with silicone, then put a row of stitches an inch back or whatever.  That would prevent slow creep.

[Thomas Conly]

I’m sorry to see that happen to your tarp Hoosier. I’ve been making stuff for years and I know how frustrating t can be to have a failure. I would agree with everything that has been said so far. If it were me, I would eliminate the reinforcement patch altogether. I noticed a couple things in your pictures that I haven’t seen mentioned.

Firstly, the webbing on your ridgeline pull out seems to be off the seam a little and slightly at an angle. When I make tarps, I make sure that the webbing is 8-10″ long and sew it onto the ridgeline with the stitches running the length of the webbing, not horizontally. This seems to help eliminate that last line of stitching taking all of the stress. I am also very, very careful to keep all my lines of stitching within the seam. This has been very strong so far, even with the lightweight Argon sil that I’ve used.

Secondly, It looks like the reinforcement patch is aligned so that the fibers are running at 45 degrees to the fibers of your tarp. It would make sense to make a patch by cutting out a square and then cut it on a diagonal. However, fabrics stretch much more on the diagonal than straight on. Even if you use the same MEMBRANE poly fabric to reinforce the tarp, you have to align the fibers the same way to ensure that it stretches the same amount.

I hope you’re not too discouraged and you keep sewing.

[Author]

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