Tape to add strength to stitched Cuben Fiber?

I have to say, the photos of the failure do look like shock loading was responsible. This is where silnylon has it all over Cuban: silnylon handles shock loading fantastically well. And that is why I have not used Cuban in my tents.

Cheers

Michael Davis:

I haven't weighed the quest outfitters tape but I have used and tested it and it appears to be much thicker than the other tapes on the market and therefore heavier. The 3M 9485PC and Venture Tape 1163 both weigh around the same at roughly 3.5 grams per yard for a 1 inch thickness (twice as wide as Quest Outfitters). This may not be super accurate as my scale weighs grams but you get the idea.

If you purchased the 3M or Venture in 1/2" width, you could reduce your tape weight in half. Edges don't need much anyway.

I don't have solid numbers for the load/time I achieved in my tests, but in my mind I wouldn't consider 10-20 pounds per second a "shock". I never bothered to load them any slower as in the real world I think it would be unlikely to see a force on your tarp slowly increase over the span of a few days. Maybe snow load increasing over a few days?

My experience has shown that cuben fiber simply snaps when overloaded. It won't stretch or at least not much – nothing like sil. Maybe Lawson has more info on that, I think (but not sure) I remember he loaded his test samples with a constant force for several days.

At the risk of giving away secrets, the shape and stretchiness of the reinforcement has bearing on strength.
The stretchiness and stitch pattern of thread also.

And as Roger has pointed out, the size of the reinforcement
too. Those photos look like pretty small reinforcements and
pretty long sewn seams on the webbing reaching far up into
the fabric.

Finally, how strong does the tie out need to be? Has
anyone sewn silnylon to cuben and pulled till failure yet?

Those photos look like pretty small reinforcements and
pretty long sewn seams on the webbing.

Agreed, I think we came to the conclusion, as Dan also pointed out that the size of the re-enforcement likely means more than the bonding method itself.

Also, with regard the the sewn seams. It appears that most manufacturers just use 2 strips of stitching to hold their tieouts. Why I decided to use a gigantic rectangle with an X in it with an additional line of stitching – I have no idea!

I would be cool to see some experiments comparing different sizes of reinforcement patches (Steve???) to see if they can successfully disperse the force.

The idea of using a larger reinforcement patch to disperse the force over more cuben seems to make sense intuitively, but the reality may not be this simple. The no stretch characteristic of cuben may mean that even with a larger reinforcement patch, the force is still focused down a similarly narrow strip of material in line with the direction of pull.

"My experience has shown that cuben fiber simply snaps when overloaded."
Yeah that has been my (limited) experience as well. Unlike silnylon, it seems difficult to visually tell between cuben that fails from a shock and cuben that just fails from a high load, because either way it snaps suddenly. Sewn cuben can fail gradually as the stitch holes stretch, but an intact sheet seems to only fail suddenly.

I'll throw in my 2cents…

I would strongly disagree than Cuben tieoutsis weaker than Silnylon tieouts or that a Properly Reinforced and Properly Stitched Cuben tieout that is shock loaded or any other type of loading will fail easier than Silnylon. Cuben is just SO much stronger than Silnylon. We mainly use the .74 Cuben and so I'm mainly speaking to this weight.

At MLD we've never heard from a customer- and thats a LOT of Cuben shelters in the field over the last 5 yrs- of any Cuben tieout failing in field use- I think the jury is well *IN* on this point. I think all the testing and theorizing is very interesting – but – no need to reinvent the wheel so to speak. Most of it comes down to skill at using a machine and the details of construction- not the material itself.

For folks wanting the use the lighter .51 Cuben- It can be OK- but it requires the next level of skill and extra reinforcement design and seam construction that adds back in a bit of weight vs using a .74 wt.

Also remembers that most small tarps are about 80% base fabric and the other 20% hardware/bonding/reinforcements/webbing. And it's maybe only 70% of the total weight in a shelter with a zipper or vent. Maybe a 5oz Cuben tarp in .74 is better than a 4oz one in .51? Hummmm….

In general to get good strength tieouts with Cuben:
1: Use large reinforcements.
2: Don't stitch too close together- spread the needle holes out- better multiple widely spaced stitching rows or bartacks than one tight one- Prevent tear-along-the- lines perforation points.
3: DONT stitch in to only one or two layers for the webbing.
4: Use a triple rolled and .5" or WIDER edge hem. The Edge is where the webbing will be stitched. If it's triple rolled then the corner intersection is 8 plies thick!

Of course- there are many other small " secrets" I can't go into. You can get some good ideas just by looking at the product detail pics we show online.

FYI: Our bonding technique only weighs 1gm p/ m per .5"" wide and the overtaped ridgeline reinforcement is only 2gms p/m at .5 " wide.

Dan,

Thanks for the information on the cuben weights. I had no idea Zpacks was using CT1K.08. Explains a lot of the weight difference!

Ron, thanks for sharing. It's something the MYOG community truly appreciate. It won't hurt your sales. You have a deservedly high reputation for your products. There is a big majority of BPLers who are more than happy to get their gear from a trusted source rather than have a go at ruining some pricey materials themselves. ;-)

"I had no idea Zpacks was using CT1K.08."

On Zpacks.com they listed their material as 0.6oz/yd cuben. I assumed it was CT2K.08 (0.74oz) and the 0.6oz number was referring to a sailmakers yard worth (28.5" x 36") rather than a regular yard, as Cuben was originally sail cloth and it's sometimes referred to in those terms.

However, a couple weeks ago I contacted Joe and asked specifically if it was 0.51oz CT1K or 0.74oz CT2K. Joe replied that it was CT1K and that he thought it weighed 0.6oz but he would re-weigh it. He then responded later saying it did indeed weigh 0.51-0.52oz. He has sorta updated the site to reflect this. Under 'Materials' it lists it at 0.51oz but other pages (ie. Shelter) still call it 0.6oz cuben.

All the different weights of cuben certainly do make it tough for a customer to understand what they are getting. Lightheart Gear is using CT0.6K for their new tent (except for the floor), Zpacks uses CT1K and HMG, BPL and MLD use CT2K to my knowledge. I'm not sure what Terra Nova and Brooks Range are doing. Granite Gear's dry sacks are CT1K.

With a great deal of research, it's tough for a customer to understand what they are getting and what sort of trade-off they are making. Hopefully Cubic Tech doesn't change their product offerings and confuse it even more. Even knowing the weight of the material (ie. 1.2oz cuben) doesn't tell you the full story because it could be the light mylar layer with loads of spectra (CT5K.08) or it could be the heavier mylar layer with less spectra (CT3.5K.18).

Also, with regard the the sewn seams. It appears that most manufacturers just use 2 strips of stitching to hold their tieouts. Why I decided to use a gigantic rectangle with an X in it with an additional line of stitching – I have no idea!

Were you using a polyester thread?

I use the thread from Thru-hiker.

Hydrophobe 100% Polyester Thread with Anti-Wicking Finish

It seems very strong but I have limited experience.

Polyester thread will not stretch as much as nylon and
could be part of the problem with seam failure.

Kind of like static and dynamic ropes and the differences
in anchor failures under similar loading events.

In my opinion cuben fiber anything should never be sewn, especially at the tie-out points. Bonding/Taping takes more time and costs more money but is the only way to go. If you need any advice whatsoever shoot me a message and I will give you an advice I can think of.

Cheers,
Lawson

Hey Roger,

>>>>>"I have to say, the photos of the failure do look like shock loading was responsible. This is where silnylon has it all over Cuban: silnylon handles shock loading fantastically well. And that is why I have not used Cuban in my tents.""

Much agreed. Nothing handles a shock load like silnylon.. I have a silnylon hammock and I have jumped into it atleast 20 times trying to make it fail. This is the same hammock with hundreds of peg holes in it.

Silnylon is really some amazing stuff.. Then again so is cuben fiber. Its strong as nails and light as feathers but it CANNOT handle shock loads like silnylon. As long as your cuben tent or tarp is pitched tight, shock loads will not be a problem. At the end of the day both materials make great shelters and they both have their pros and cons.. Neither of them are perfect.

To me the perfect material is… Silicone coated Dacron.

Isn't silicone-coated Dacron just what we always call Spinnaker fabric (like Spinntex)? Are you being sarcastic, Lawson? I thought you disliked spinnaker (low tensile strength, unreliable waterproofness, etc.)…

Dacron doesn't stretch much either. Hence is weaker than
either spectra or nylon under shock load.

>>"Isn't silicone-coated Dacron just what we always call Spinnaker fabric (like Spinntex)? Are you being sarcastic, Lawson? I thought you disliked spinnaker (low tensile strength, unreliable waterproofness, etc.)…

Actually most spinnaker cloth is nylon because of its light weight, high tensile strength, superior abrasion resistance and flexibility. Nylon has a few main drawbacks though… Its has low UV resistance, absorbs water, and has low modulus allowing too much stretch. Sailer's don't really care about UV resistance and water absorption but they do care about stretch so in order to fix the problem they coat the living hell out of it with urethane. This firm coating works great for spinnakers but awful for tarps and tents. It creates a material that is loud, tears easily and has very unreliable water-resistance qualities. (new spinnaker works great but crinkled up stuff leaks like a sieve)

A silicone coated Polyester/Dacron on the other hand would be nothing like a spinnaker cloth and would give Silnylon a serious run for its money. The three most common complaints about nylon in the backpacking world is how much it stretches, how it absorbs water and how it has low UV resistance. Polyester/Dacron would fix all the problems with its low stretch, Low absorbency of water and it's high UV resistance. In addition to that it has excellent resiliency, high abrasion resistance, high flex strength, high tensile strength and is easily recyclable.

I agree a polyester/dacron has less shock resistance then nylon but it has ALOT more then cuben fiber.

I don't know the number's for cuben fiber sense they don't publish them but I would say it's elongation at break is less then 3%.

Nylon 6,6 is something like 17-35%
Polyester/Dacron is something like 12-25%

Numbers depend on the fiber size, weave type, and coating.

Lawson,

I thought most spinnaker, as used for backpacking, is sil-poly. I know SpinnTex EXP is labeled that way according to thru-hiker.com and MLD. MLD seems to really know there fabrics, so I doubt this is a misunderstanding on their part.

>>"I thought most spinnaker, as used for backpacking, is sil-poly"

Negative… Its heavy urethane coated nylon or polyester with a silicone coated after thought.

Spinntex as you said is a polyester spinnaker material used by MLD yet Gossamer Gear uses a nylon spinnaker material so in order to determine if most spinnaker material is nylon or polyester we would first need to know which one of these companies sells more spinnaker shelters. As an industry whole most spinnaker is nylon.

I think nobody disputes that the term "spinnaker" refers to a whole family of fabrics of varying composition. Clearly most spinnaker fabrics are nylon. There are also PET (Dacron) and even PEN (Pentex)spinnaker fabrics, and the coatings can be urethane, silicone, melamine, or polycarbonate. They are called spinnaker fabrics to denote their application, not their composition.

It also has to be conceded that in the casual parlance of these forums, and in the lightweight backpacking community in general, the term spinnaker is used (inaccurately) to refer specifically to very light coated polyester like Spinntex. For shelters, for example, the MYOG crowd typically considers three material options: silnylon, Spinntex, or cuben. When they refer to the Spinntex, and debate its pros and cons on the forums, they often just call it spinnaker, which, to them, means silicone-coated polyester. I'm sure that you are aware that the term spinnaker is used this way, Lawson, and I acknowledge that you object to it.

I posted a question to you about Spinntex because you have said that you disfavor it for shelters, and yet you feel that a silicone-coated polyester would be an ideal shelter material. In other threads you have said that you dislike 0.75oz and 0.95oz spinnaker fabrics in general because they have poor strength. Would you favor both a heavier PET fabric (1.35 oz?) and a heavier sil coating than Spinntex? What specs would your ideal silpolyester have?

"
I agree a polyester/dacron has less shock resistance then nylon but it has ALOT more then cuben fiber.

I don't know the number's for cuben fiber sense they don't publish them but I would say it's elongation at break is less then 3%.

Nylon 6,6 is something like 17-35%
Polyester/Dacron is something like 12-25%

Numbers depend on the fiber size, weave type, and coating."

Note that climbing webbing is either nylon or nylon/spectra,
not Dacron Polyester, and the nylon/spectra can sustain
higher loads in relation to the weight of the webbing
than all nylon.

Spinnaker has been made for years out of various Polyesters,
but when a race boat wants the lightest, strongest, they
use one of the laminates that contain high strength fibers
like Spectra/Dyneema.

I suppose tho that a light sil/polyester fabric might
be weak enough to pass flame retardency tests as the fabric
might melt away from the open flame quickly enough to go
out. I wonder tho if polyester is absorbent enough to
keep it's sil coating well?

Think 30d polyester with a thick silicone coating. Most likely were talking a 1.5oz finish weigh..

IMO, there is a worthwhile distinction to be made between "stretch" and "sag" in silnylon and some other fabrics.

"Stretch" is the ability of nylon to do just that when exposed to pressure, as from a pebble under a tent floor, which in turn is under us. It is good, because it prevents the fabric from tearing or abrading.

"Sag" is what silnylon does when exposed to temperature changes. It is bad, because it destroys a taut pitch, reduces space inside a shelter and in a high wind creates billowing, snapping and possibly wind pockets that will knock the shelter down. Of course, this doesn't matter so much if the nylon is being used for a floor, rather than a fly or canopy.

The sag in nylon appears to elongate the threads running with the fabric grain, as well as diagonally; whereas at a constant warm temperature, the fabric appears to be stretching only diagonally to the grain.

Can we have one without the other? Not in any silnylon I've tested so far. But there are polyester fabrics available with a 'soft hand' and a good degree of stretch, as Lawson points out, that do not sag much, if at all.

More on thread, would still like to know what you all think about using bonded strips of cuben as a very light tape to reinforce stitch lines on cuben flies and canopies.

Thanks,
Sam

Samuel, I think the cuben strips bonded over a sewn seam is a good idea if you want to improve the strength or resistance to water penetration of a seam that has already been sewn, but if you are making plans to make your own shelter and haven't begun fabrication yet (and are open to doing some gluing), I would skip the sewing and just bond.

If you bond a strip of cuben over a sewn seam, the strength of the seam will not be the sum of the two seam types. The stitching in a sewn seam (even when low stretch thread is used, like kevlar) will have a little bit of give. The loops of thread will twist and bow in response to strain, and the sewn seam will therefore have some "stretch" even if none of the components are actually stretching. The strips of cuben on top will have almost zero stretch, and will therefore bear essentially 100% of any load applied to the seam. The stitching will hang there, unchallenged, and fail to serve any purpose any longer.

It might seem that the stitching could serve as a back-up fastener, so the panels of the shelter don't actually fly apart if a blast of wind causes the bonded cuben strip to fail, but remember that failures of bonded cuben seams occur at the edge of the overlap, on the outside edges of the seam, so the stitching would just end up one one side or the other of a wide open tear.