Tape to add strength to stitched Cuben Fiber?

[Christopher Kayler]

Hi all,

I'm interested in purchasing a cuben tarp that is much lighter than other options. However, those other options happen to be taped seams instead of stitched. I've gathered that taped seams tend to be stronger than stitched, but for the weight I'm learning towards trying out the stitched tarp and just adding tape. Is this a lost cost, or will the strength be generally increased? Any recommendations on tape if this is a good idea?

Thanks,
Chris

[drowning in spam]

One of the guys from Cubictech said taping is a good idea.

[Colin Krusor]

A lot of anecdotes posted to this forum suggest that, for cuben fiber, sewing alone is not adequate for high-strain attachments or seams. If you want to go with the sewn tarp, I would highly recommend adding additional tape or adhesive at tie-outs and other heavily loaded spots.

Some people are very opposed to sewing cuben, although sewing is still pretty commonly used for cuben articles by cottage manufacturers. Taping is also widely used for commercially available cuben gear. An excellent comparison of available tapes was posted to Hammockforums awhile ago. I have heard several stories about tape peeling away from cuben in extreme cold, but I don't know which tapes might be susceptible to this, or how common it really is. Some tapes are actually a film of gummy adhesive on a removable carrier paper, and can therefore only be used between two layers of cuben, not on top of a seam that has already been sewn.

There is a general consensus, I think, that bonding with adhesive gives the strongest and lightest seams. There are a few bonded cuben tarps on the market.

[Mark Hudson]

While I have no experience in manufacturing cuben products, I use a variety of tapes in my business every day.

We manufacture aluminum and steel structures and you would be surprised what we can bond using only tape.

I would however question the ability to take a previously sewn seam and tape it effectively.

Again, no real experience, but based off my cursory knowledge, I would at least get this answered prior to purchase.

[Dustin Short]

Usually if any taping is to occur, the seam is taped FIRST followed by sewing SECOND.

This gives you the best taping possible while still allowing a sewn seam. Although it's looking more and more like taping alone is stronger, lighter, and more watertight than sewing or sewing and taping.

[Christopher Kayler]

Thanks for the replies guys. It's seeming like taping first/only is the way to go, as opposed to getting a poor result of trying to tape on top of something that is already sewn. I may have to go with a different tarp that is taped instead of sewn, as durability is a concern for me … even though the sewn tarp is larger dimensions and lighter, and less expensive. Should I really be this worried about the sewn stuff … tough choice.

[Dan @ Durston Gear]

Can you give us a little more specific info on what tarp you are looking at? Since it's sewn cuben, I imagine you're looking at a Zpacks tarp? Try contacting MountainFitter.com and getting a price from them for a bonded cuben tarp of similar dimensions.

[drowning in spam]

My sewn & taped Hexamid is till going strong. The only elongated stitching holes I've seen are because a few people tripped over the front guyline. I believe I bought it in February, but I've probably only pitched it a couple dozen nights so far.

[Richard Bolt]

I taped and then stitched my home made cuben tarp – with several layers of taped cuben where I sewed the webbing for tie outs. I used an appropriate double sided tape for the task and I had major hassles with the needle gumming up during sewing. If I did it again I'd likely go with an adhesive and then sew.

It has proven itself very strong and durable -it's had about a year of good usage so far.

[Christopher Kayler]

Dan,

That is correct, the Zpacks Hammock Hex Tarp.

Mountain Laurel Designs as well as Hyperlite Mountain Gear both offer tarps of nearly the same dimensions (they are actually slightly smaller than the Zpacks), yet they weight more while being more expensive. I'm just worried about the durability of the Zpacks one since it is stitched. A member of Hammockforums.net had a stitching hole already elongating on his Zpack hammock tarp, and I believe Joe reccomended duct tape. I've always been happy with Joe and his service, but I'd be bummed if that happened to me. Maybe that doesn't happen on all of his tarps, who knows?

[Christopher Kayler]

Hi Eugene,

Did you tape it after receiving it? What tape? Joe used to do taping, but has since stopped … perhaps you received an earlier one with the tape?

[Michael Davis]

I have also been contemplating a cuben tarp but I am confused about the weight of the tape. I checked Quest Outfitter (link below) and they claim the 1/2" tape weighs 3.5 grams/yard. That is basically the same as 3/4" grossgrain!

They also sell 1" wide tape, which is what I would use on the ridgeline seam, so I guess that would weigh about twice as much. If I use the 1/2" around the perimeter edge to reinforce it, all that tape would add up to 2-1/4 ounces. Considering that my tarp material weighs only 4-1/2 ounces, that is a ridiculous ratio.

Does this make any sense to you seasoned cuben craftspeople?

I can actually make the tarp from Spinnaker for the same total weight (with rolled edges), and for half the price. Of course the only problem is that I can't find Spinnaker EXP anywhere right now.

Check the bottom of the page here … http://www.questoutfitters.com/coated.html#CUBEN

[Sam Farrington]

Thanks – this is the update I was looking for. If I stitch .51 oz cuben, will bond a strip of cuben, at least l" wide, over the stitch line before sewing, and bond triangles at all corners, also before sewing. Realize bonding alone would be better; but will be attaching different fabrics and zippers (zipper tape)to the cuben; so think stitching will be best.

[Dan @ Durston Gear]

"I checked Quest Outfitter (link below) and they claim the 1/2" tape weighs 3.5 grams/yard."

I wonder if that is the weight of the tape including the backing on both sides? If it is, it would be way lighter once it's applied. 3.5g/yd does seem heavy if it's for just the tape. Perhaps you could use it selectively (ie. the ridgeline) and sew in less stressed areas (ie. the perimeter hem). I've ordered some so I should be able to speak to the weight of this tape in a week or two.

"Dan…That is correct, the Zpacks Hammock Hex Tarp.

MLD as well as HMG both offer tarps of nearly the same dimensions (they are actually slightly smaller than the Zpacks), yet they weight more while being more expensive. I'm just worried about the durability of the Zpacks one since it is stitched."

Both MLD and HMG are using CT2K.08 (0.74oz/yd2) while Zpacks uses CT1K.08 (0.51oz/yd) for their tarps. That's a big part of the weight difference. CT2K.08 contains double the spectra/dyneema as CT1K.08, so it's significantly stronger. CT2K.08 is also about 5% more expensive which explains some of the price difference. The rest of the price difference is because thread costs almost nothing, while high end double side tape is somewhat expensive.

The rest of the weight differences would be to the weight of bonding vs. sewing, and due to the weight of the reinforcements and guyouts. I have an HMG tarp and it is very well reinforced with generous patches of heavier cuben. Overkill maybe…but it instills a lot of confidence in the tarp and it's hard to complain about an extra 1/2oz because the reinforcements are bomber. Looking quickly at the photos online, the Zpacks guyouts/reinforcements looks quite a bit lighter than the HMG ones, and MLD falls in between the two. I can't speak to the actual strength of the tie outs since I haven't tested them….perhaps all of them are plenty strong.

"I can actually make the tarp from Spinnaker for the same total weight (with rolled edges), and for half the price. Of course the only problem is that I can't find Spinnaker EXP anywhere right now."
I wouldn't….cuben is just so much better than Spinnaker and when you are making it yourself the cost difference isn't that radical. Cuben is more waterproof, way stronger, non saggy, longer lasting and isn't noisy like Spinn. For a MYOG tarp you are probably using 5-8 yards of material which means the cost difference is maybe $10-15/yd or $50-$120 total. That's money well spent IMO for a better tarp that is going to last way longer and be worth a lot more should you choose to sell it. Also if your skills are limited, bonding a tarp with double sided tape is way easier to learn than sewing.

"Should I really be this worried about the sewn stuff …?"
Generally speaking, I don't like the idea of sewing two cuben panels together (ie. a ridgeline), but I don't have a problem with sewing stuff like guyouts as long as the area is well reinforced. On a guyout, if you've usually got the edge of the cuben folded over to be 2x as thick, and then you've got a reinforcement patch on there too, you are sewing through 3 layers of cuben at least so the stitch holes stretching isn't an issue. With stuff like ridgelines, it's hard to reinforce the cuben so the stitch holes don't stretch, and if you do reinforce it you are likely using bonding to do so, so why not just bond the actual seam?

[Javan Dempsey]

Well taping isn't the only way to bond cuben, but it likely is the most expensive methodology. It is however easier than the other options, or than sewing.

Cuben equipment prices are pretty up in the air right now anyway.

"Both MLD and HMG are using CT2K.08 (0.74oz/yd2) while Zpacks uses CT1K.08 (0.51oz/yd) for their tarps. That's a big part of the weight difference. CT2K.08 contains double the spectra/dyneema as CT1K.08, so it's significantly stronger."

How significant is this really when the weak point regardless is the bond/seam/whatever? Even if the bond is the strongest of the "thus far observed" type, the failures still occur at the bond, in said best case; by failure of the laminated mylar, not the spectra

My point: Unless you can create a bond as strong as uncut, non-seamed, non-bonded Cuben(read: continuous uncut/altered piece), you're wasting money on a higher spectra count. Better money would be spent on a cuben model with a thicker outer laminate, because that's going to fail before the UHM.

When I start seeing uncut/seamed/bonded/joined piece of cuben that fails catastrophically(thus far only Lawson's hammock?) , that's when I'll concede the 'more spectra needed' argument.

[Dan @ Durston Gear]

"Even if the bond is the strongest of the "thus far observed" type, the failures still occur at the bond"

You make good points, but I suspect the guyouts are the weakest part of any tarp. As per Steve Evans experiments, the corner guyouts tend to fail right where the reinforcement patch ends and leaves just the single layer of cuben. With bonded seams the force is generally dispersed out over a fairly large area, so enough force could exist to tear the cuben near a guyout, without causing failure at a less strong bonded seam.

Photo: Steve Evans, Sulak46.com

My guess is that virtually all cuben tarps would fail at the guyouts first if they were tested to failure, so using heavier weights of cuben does increase their overall strength. The question is really are the tie outs on CT1K.08 strong enough to withstand years of reasonable use? This is something we'll know better with time. I'm all for pushing the limits, but at the same time when I'm the one spending hundreds of dollars I don't mind an extra ounce for a tarp that's 60-70% stronger. Significant snow loads may be one thing that causes trouble for CT1K but I'm just speculating.

I know MLD has done a lot of experimentation with different weights of cuben and they choose CT2K. Perhaps most telling, BPL choose CT2K for their new 2010 tarp instead of CT1K like they used to use because of failures. Here's a quote from BPL:

"We use a very strong 0.8 oz/sq. yd. (27 g/sq. m.) Cuben Fiber that is actually heavier, and has a higher tensile strength, than the old 0.6 we used to use, but our bonding methods saved so much weight we decided to spend it on more robust fabric, since we saw a few fabric failures in high winds with the old stuff."

[Javan Dempsey]

Dan,

I hadn't seen those pics before, interesting. Looks to me that the failure actually occurs from where the stitching pierced the laminate, causing a typical mylar style tear and then pull-out of the spectra.

My thought is that if I did have to sew a hem/seam, fold the edge over and bond with an adhesive, and then bond a homemade bias strip of cuben on the other side with the spectra aligned in the opposite direction or on a 45deg orientation. Then sew thru.

edit: spelling.

[Dan @ Durston Gear]

I edited my previous post a whole bunch of times, so if you didn't see the bit about BPL switching to CT2K instead of CT1K due to failures in high winds then have another read.

For more info on the guyout failure shown above and other ones Steve Evans tested, check out these documents:
http://www.suluk46.com/documents.html

He did video the failures and as I recall, they did not start at the stitching holes on the sides. I believe that because cuben isn't stretchy (which spreads the force), the strain is focused down a fairly narrow path of cuben in line with the direction of pull. This starts a tear in the weaker unreinforced cuben and then that tear almost instantaneously spreads.

Here's some more pictures. This is CT0.3K. Heavier weights of cuben should fail in a similar manner but under higher loads of course. Steve was testing different sewing & bonding methods for the guyouts in this experiment, but the testing appeared to show than (with the exception of sewing) the material failed at the edge of the reinforced area, so what mattered was having a larger reinforced area (or stronger cuben) rather than the actual bonding method used. Even a larger reinforcement wouldn't do much if the stress is focused down a narrow path of cuben, so the best way to raise the failure threshold is stronger cuben. Have a read for yourself though. Steve does a much better job explaining the results and conclusions than I have:

[Rog Tallbloke]

"the failures still occur at the bond"

From what I've seen here on BPL, the failures occur at the edge of the bond. It's a material failure rather than a glue failure. I suspect the problem might be stress raisers caused by thicker lines of glue oozed out from the edge of the doubled material. I'm going to take care to wipe the joint edges to try to minimize this.

I'm also going to use stretching sections in the tie-outs to minimise shock loads when the wind gets up and flaps the material. A cheap option here is to use rings cut from a punctured motorcycle tyre inner tube. This will add significant weight, but I'm as interested in the total watproofness and non-sagginess of cuben as much as it's lighter weight so this is a price I'm willing to pay, because I'm not willing to pay the price of aother 7m of CT2K08!

I have bought CT2K08 for my project. Nearly 70% stronger in tensile strength for a 30% increase in weight, and still ~half the weight of silnylon. It's the best compromise IMO, but I am wanting a tent which will survive a year long trip, rather than pushing the bleeding edge of ultimate lightness.

[Dan @ Durston Gear]

"I'm also going to use stretching sections in the tie-outs to minimize shock loads"

This sounds like a good idea to me. It shouldn't take much stretch to take the stress spike off. You could tie an inch of 3/32" shockcord to the tie out, and then tie the guyline to that and use a micro LineLoc. Total extra weight maybe 1g/tie out. I would use shockcord over a rubber inner tube because motorcycle inner tubes are heavy and a full ring seems like a lot more than you'd need. You can get shockcord for dirt cheap (ie. $0.50/yd) and in a variety of thicknesses to get the exact stretchy-ness you desire. I suspect an inch or two of 3/32" shockcord would work great because it can stretch to nearly double it's length and I think it's a good stiffness. 1/16" is pretty weak and 1/8" would probably work well too and it's not that stretchy so you could get a taut pitch with still a bit of give.

[Javan Dempsey]

Interesting for sure, although considering the reinforcement and the way this was loaded I guess it's not surprising. Looks like the edges are rolled multiple times, or at-least 1.25 times and obviously the stress is propagating directly in line with the tie-out regardless.

However, I don't think this really applies to seams, which is what I was referring to about laminate failure from bonding. Multiple bond methods have stripped the mylar right off other layers in sheer.

I haven't read Steven's docs yet, too much info to process some days and I should probably be sewing right now and not typing… ;)

[Rog Tallbloke]

"I would use shockcord over a rubber inner tube because motorcycle inner tubes are heavy and a full ring seems like a lot more than you'd need."

Thanks Dan, good advice. As you say, it's just the spike in a sudden gust and the 'snap' as the sheet flaps back taut that needs to be softened.

[Dan @ Durston Gear]

"Multiple bond methods have stripped the mylar right off other layers in sheer."

I've seen experiments where this has happened, but I've never heard of a failure of a bonded seam in the field. I suspect it's because in the real world the forces are rarely concentrated on one small area of the seam like they are in seam strength tests. It seems to me that seam strength isn't as important as tie out strength because of the way stress is focused at tie outs but dispersed along seams.

[Javan Dempsey]

I concede that observation to likely be correct Dan.

[Rog Tallbloke]

"It seems to me that seam strength isn't as important as tie out strength because of the way stress is focused at tie outs but dispersed along seams."

This was one of the things I liked about my old Ultimate 'Tramp'. It was a traditional tent shape, but used an A frame in pole sleeves at the front end. So the stress on the largest sheet areas was spread along the seam rather than concentrated at the tie out. I was considering using nylon for the pole sleeves to handle the abrasion, but it's hard to see how best to attach these to the cuben. Maybe the gel coat on cf golf club shafts won't abrade the cuben anyway. Thoughts?

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