Width of cuben bonded seams

my wiki entry might be a start

Where is your wiki?

Nevermind, I didn't dig far enough. I found it.

The wiki entry is good for talking about adhesive and seam strength. Are there any good resources on how to handle the material. Things like, best way to cut it, what kind of seams to make, best way to reinforce the tie-outs on a tarp.

Sorry, I'm clueless and I am kicking around the idea of making a tarp.

Cutting Cuben – You can't really cut it with scissors because it's so thin. Even good sewing scissors won't give you a clean cut. Using a cutting board and a razor blade/exacto/stanley knife/scalpel works pretty well. Even better is a 'hot knife' which is essentially an exacto knife but heated to 950F so it cuts with very little effort. For small projects this is likely unnecessary but it's nice to have for larger projects.

Seams – You want everything to be in 'sheer' rather than 'peel' if you are bonding/taping the seams. Do a google search if you don't understand these terms. A 1/2" overlap should be fine if you are achieving a quality bond. A 1" overlap is what I have normally used but it seems like overkill. In the future I'll likely use 0.5 – 0.75" overlap.

Bonding – I've used Hysol U-09FL for a cuben tent fly. More recently I've been using SeamGrip to make some stuff sacks. The Hysol seems to have worked well but I haven't tested it to failure so I'm not sure of the ultimate strength of my bonds. SeamGrip is what I've been using the last couple weeks and I've been quite happy with it. Unlike Hysol, there isn't two parts to mix correctly and it's cheaper and readily available. It's also faster drying which I like. With Hysol you can still manipulate the bond for 30min-1 hr after gluing and it's not very strong at all until +24 hrs. SeamGrip only has a 5-10 minute working life and it's impressively strong in peel and sheer after just 30 min. You mentioned using tape, I think 3M-9485PC is a popular choice. QuestOutfitters sells a tape for cuben taping that probably works good too but it is kinda expensive in larger quantities.

If you are bonding straight seems then tape is a quick, easy way to do it. However, if you are bonding curved seams that are more complex then an glue is going to be easier to use since you have time to adjust it before it sets.

Tie-Outs – In my opinion, it's best to use cuben to reinforce the cuben. Unlike cuben, fabrics have stretch to them so if you sew fabric to the cuben and then attach the tie out to the fabric, then the stress can be concentrated on a few stitches as the fabric stretches. I've been happy with my tie outs that involved folding a strip of cuben into a strong strip, gluing that to the tarp and then gluing reinforcement patches over that and pressing it while it dries. I used 1/2" wide strips that fit perfectly into LineLoc3 tensioners (available at Quest). You could sew this as well later if you want as a backup but it seems awfully strong just like this. LineLoc3's are ~1.2g and then it's another 1.2g or so for all the cuben patches and strip, so in total you're looking at ~0.1oz/tie out.

Thanks a lot, that's the kind of experienced info I was looking for.

As for a hot knife I can just fix an exacto blade to my soldering iron.

The tape seems pricy but if I make anything at all it will be one tarp, likely a 6×8 or something similar.

What cuben fabric weight do you prefer for tarps?

It looks like all of you edges are folded and glued as well, is that the case?

Also when glueing/tapeing those long seams do you have to keep them under pressurd until the glue dries? if yes, what method did you use to keep them under pressure? Do you glue and put weight on small bits at a time? Any concerns about your clamp/weight sticking to the glue?

Also, by you picture, since your tieouts are at a 90 degree angle are you using those crners as storm flaps. Seems like on a standard pitch (A-Frame) it may be better to glue the tie out straps at a 45 degree angle.

Sorry to pepper you with all these questions. Cuben is expensive and if I do this I don't want to screw up.

Did a google on 'sheer' seams and got some great hits on frilly ladies undergarments. Searching 'peel' 'seams' and 'cuben tarp' are not helping me.

"What cuben fabric weight do you prefer for tarps?"

I used CT2K.08 cuben which is weighs 0.747oz per square yard. This is the same stuff MLD, BPL, Zpacks etc are using for their shelters. This is good stuff and quite strong. You could go lighter if you're looking to make SUL gear but the weight savings aren't huge and the thought of an expensive cuben tarp failing is hard to stomach. I know MLD used to make (still makes?) a 0.33oz cuben tarp (CT0.3K.08?) but even they say it can fail in the field.

EDIT: This is not true. MLD has never used 0.33oz cuben.

"It looks like all of you edges are folded and glued as well, is that the case?"

Yes they are. I did this mostly to finish the look, but it would also minimize risk of a tear starting. I did a 1" fold but that was way overkill. For simply finishing an edge 1/4" or 1/2" would be lots.

Regarding pressure, I used pressure when I could but a lot of my seams were complex 3D shapes because this project was replicating the fly for a dome tent. Accordingly, it was not possible to lay the seam flat and then press it. I did press the areas that I could like the tie outs. I'm sure pressure is the ideal way to do it, but without a complex 3D jig I couldn't do it. I know others have also not used pressure (ie. Steve Evans) and had good results. I perhaps could have glued the seams a little bit at a time but this project was already extremely time consuming. With Hysol you'd want it to sit for at least 12 hours. With SeamGrip you could probably press it for 2 hours and then move on. With Hysol it seems that it only sticks well to plastic. So heavy metal pots filled with water worked well to press things. SeamGrip is fairly sticky stuff so you'd want to be careful not to slop too much outside the seams. With tape you should be able to have minimal adhesive exposed.

Re. 90 degree angle vs. 45 degree. Here is a better look at this application. That previous pic I posted was at the bottom of the zip.

Regarding sheer vs. peel, shear is when the material is overlapped, so if the seam fails it will fail all at once. Peel is when the seam will slowly peel apart if the adhesive is failing. Generally, shear seems will be a lot stronger because peel concentrates the forces. Simply overlapping the two pieces of cuben and gluing them as you see in the photo above is shear. There is a bit more to it than that, but essentially you just don't want to design seams that can peel under strain.

Good work on the fly. I was thinking of something less elarborate like a flat tarp for myself.

Thanks for the cuben chart.

So you did an overlaped joint for your ridgeline. Which you would have to do with glue (unless you cut a strip to run along the ridgeline).

I guess peel would be a taped abutted joint? That make sense to me but an overlaped joint with tape would have to be taped on both sides, I would assume.

Where does one procure the glue you are using?

I still need to put some thought in to this, logestics, pricing….

It looks like I can get a tarp from ZPack for about the same as my material cost. Unless someone has a source for cuben that is less than $27 a yard.

Yeah I did a simple overlapped joint with a 1" overlap for basically everything. If you wanted to do the same thing with tape you would just need to use a double sided tape like the 3M tape and the one from Quest.

Scroll down to the bottom of page one on this thread and there are some really nice peel vs. shear diagrams:
http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/32998/index.html?skip_to_post=291170#291170

Regarding material costs, my cost from Cubic Tech for olive drab CT2K.08 was $23.46 per square meter plus a $15 handling fee for the order plus shipping. Non colored (white) cuben is a bit less ($1-$2) still.

Dan pretty much knocked it out of the park with his answers. I'll just echo his comments about the tieouts made from cuben – they look great and are no doubt better then using 2 dissimilar materials.

If you want to make a flat cuben tarp, you can always follow this guys videos (minus the grossgrain tieouts). I find him quite knowledgeable and fairly easy on the eyes. ;)

Part 1
http://www.youtube.com/watch?v=UdTCBJ2lH4U

Part 2
http://www.youtube.com/watch?v=nX1s04_jhls

Enjoy!

Thank you for the info and the links! As always, lots of good posts are buried in old threads…

My initial idea is to use tape because it’s the material that I can find more easily. However, I find some of the recommended glues, perhaps I use it.

@Dan: Your tent fly looks great! Regarding tie-outs and reinforcements, I also think that using cuben is better because you don’t mix materials and reduce the sewing (severe stress points)

@Steve: I’ve already seen those videos. The things that makes this guy are awesome ;-)

@Derek: I finally found and read your wiki entry about cuben. Very informative too!

I also can’t find Hysol here in Spain. For this reason I plan to use the 3M tape.

Thanks Steve,
Those vidoes helped a ton. I am a visual learner. The videos would have been better if that guy in them wasn't so hard to look at :)

So your SUL tarp looks to be 1 strip of 54-60in wide cuben, therefore no ridgeline to sew?

What are folks thoughts on sewing verses bonding?

Regarding sewing vs. bonding, I favor bonding but sewing can work well too if it's done right. There's a big anti-sewing cuben movement going on right now, but I don't think it's as simple as that. When you sew cuben, you just need to be sewing enough layers that the stitches aren't going to stretch larger holes in the material. So if you're just overlapping two pieces of cuben and sewing them together then you'll likely run into this problem. Just one or two layers of cuben isn't strong enough to prevent sewing holes from enlarging and perhaps ultimately tearing out. Even if the seem doesn't totally fail, it looks poor and it's hard to seam seal if the holes keep growing.

What you could do if you wanted to sew two panels of cuben together is to fold the edges of the panels first so the material is double thickness at the edge and then overlap that, so you are sewing through a total of 4 layers of cuben. 4 layers of cuben is awfully strong and the stitch holes shouldn't enlarge under reasonable use. This may not be the most ideal way of connecting these panels but it should be a solid way of doing it that won't fail you. In general, I would say that sewing 2 layers of 0.7oz cuben is too little (for something highly stressed), 3 is borderline and 4+ is going to be fine. Even sewing two layers is fine if it's not a high stress application. I have some cuben stuff sacks that are sewn with just 2 layers and they are doing great.

There are some situations where sewing may be preferred over bonding. The only example I can think of is when a join is unavoidably going to be stressed in 'peel' rather than 'shear'. Even the best bonds make me a little nervous if they are designed in peel, whereas I would feel fairly comfortable with the same join sewed, provided there is enough layers of cuben so the holes won't stretch. An example of this is the top of a stuff sack where the cord runs through. If you fold the top of the stuff sack down (like rolling up your pants), leave a gap and then bond it to create a channel for the cord, then this bond is going to be stressed in peel a little bit because of the thickness of the cord. I've probably lost you here because this is confusing stuff to explain.

Here's another way to look at it. In the picture below, the tie out points are designed largely in shear, but there is a bit of peel forces going on because of the black plastic bar than runs through the loop of cuben. Since the bar is a few millimeters thick, it wants to peel open the loop of cuben. In this case the peel forces are pretty minor, but there are still some at work. If I was to sew a few stitches along the edge of the fly right where the cuben loop exits, then I would eliminate any chance of this join peeling open. I have actually done this and sewed a small box at each tie out. I didn't do this because I didn't trust the strength, but because I couldn't think of a good reason not to. In this case I'm sewing through 8 layers of cuben, so any stitches are going to be very strong and not stretch larger holes.

"I also can't find Hysol here in Spain. For this reason I plan to use the 3M tape."
I got my Hysol from Steve Evans. I don't know if he has any more or not. Using the 3M tape should work well, but you might want to have a glue on hand as well. Tape should well for joining seams, but you might have troubles using it if you need to join larger areas, like bonding on large reinforcement patches. If you're bonding on a circular reinforcement patch then it would be hard to fully cover the mating surfaces with tape.

FWIW, yesterday I did a bit of testing on SeamGrip. After 24 hours of drying (ie. fully dried) it could still be picked and pulled apart in peel with moderate effort, but in shear it was very strong. A 1" x 1" bond was stronger than the material in shear. I had to pull almost as hard as I could and then the cuben failed and there was just strands of the inner fibres handing where the cuben had pulled apart.

Dan, could you post a photo of the failed cuben (with the hanging fibers)? I've been concerned that delamination might be the failure mode at simple overlapping seams (breakage of the film and fiber pull-out), rather than clean, extensive breakage of the reinforcing fibers. I bonded on both sides on the ridgeline (with ribbons of cuben) of the tarp I made this spring, but perhaps that wasn't necessary.

Derek, in your extensive tests, have you found that simple overlapping seams fail by fiber breakage rather than just film breakage, delamination, and fiber pull-out? Is a double-sided seam overkill? Dan, Steve, what are your experiences?

All my seams have been like your diagram A. This seems to be plenty strong unless the seam starts to peel for whatever reason and that reduces the width of the bond so much that it fails. I think you'd easily be able to see this coming though and take preventative action.

Regarding SeamGrip failing. What I did was a glued the following seam together like your Diagram A with an eyeballed 1" overlap. I then picked the top corner up and then peeled the seam apart from top to bottom. It wasn't that hard to do, but still strong enough that I don't think it would rapidly happen in the field. Shortly before I had the seam full apart, I though to see how strong it is in shear. The actual amount of seam left intact was less than an inch wide. It was maybe 1/2 – 2/3 of an inch wide and an estimated 1" overlap. I pulled the two sides apart in shear and the failure was difficult to achieve. I was pulling pretty darn hard on a relatively small amount of bonded surface before I got this failure:

"If you fold the top of the stuff sack down (like rolling up your pants), leave a gap and then bond it to create a channel for the cord, then this bond is going to be stressed in peel a little bit because of the thickness of the cord. I've probably lost you here because this is confusing stuff to explain."

This situation is showed in the following diagram (not to scale). When you apply a force to the black circle (cord, lineloc…) the horizontal components (green arrows) create peel forces at the seam. So, to minimice this forces, you can increase the loop size (A distance).

Another situation that comes to my head where sewing is inevitable is when you join Cuben to a piece of cloth (a zipper for example). According to you, it would be sufficient to fold the cuben along the sewing line (or even adding a reinforcement strip if the sewing line would be stressed)

I am afraid I have thrown away my tested samples now. I certainly saw failure like Dan's photo. I saw complete fibre failure along the edge of the glue area, fibre failure mixed with film failure. Complete film failure where the "weft" came away with the glue leaving the "warp behind (like Dans photo). Remember I was testing 1" wide strip not corners of fabric. My feeling is The lighter the cuben the more likely complete fibre failure is. Is it not the case that film failure happens when the area under stress is smaller. You can make the area bigger with a wider simple overlap or with ribbon glued on both sides, or a simple overlap and a ribbon on one side I suppose. With a big enough area of glue you nearly always get fibre failure. I am thinking In shear not peel.

All of my tests have been with the lightest version of cuben available (0.33 oz/yd^2). The fibers almost always break with the film. The double seam may be overkill depending on the strength of you material but you would have to test it to see. I haven't had a joint/seam fail before the material when using the Hysol but I have had this happen using 3M tape.

I actually just finished testing another method the other day using 0.33 cuben, Venture tape, and Hysol.

I overlapped the cuben by 1" and taped it using venture #1163. I then took a foam brush and applied small lines of Hysol on the overlapping edges (think seam sealing the bonded seam). I did this with the logic that this would help prevent peel failure. I tested it and the seam held fine until the material failed (I can post pics later tonight). I may do a "head to head" comparison with the Venture/Hysol combo versus the Hysol alone. Could be interesting!

Nice diagram Marco! That is exactly what I was trying to explain. It seems that for the purposes of a stuff sack, these peel forces are minimal enough to be a non-issue, but it is something to think about. MLD & MountainFitter are both selling full bonded drawstring stuff sacks, so they must be confident these peel forces are minor enough to be a non-issue.

For something like a stuff sack the overall stresses are usually pretty small compared to something like a tent or tarp, so sewing is likely fine. It also doesn't matter nearly as much if the holes do stretch a bit. I've done it both ways and sewing is a LOT faster, but bonding gives a nicer looking result. For the drawcord area, one could also bond and then sew it along the top of the bond to prevent any peeling.

Regarding zippers, it may actually be possible to bond a zipper into place if you are using a waterproof (Uretek) zipper. From my experience, the Uretek actually bonds decently well to cuben, because it seems to also be some sort of a plastic. I considered doing this with my cuben tent fly, but I was just too nervous to guinea pig this technique so I sewed it. When I sewed in my zipper, I folded the cuben over 1" and bonded it. Then I sewed the zipper to that. [confusing explanation ahead] This is only two layers of cuben being sewed, but both layers are bonded together before sewing which seems stronger than sewing 2 non-bonded layers, and secondly, both layers are working in the same direction so they are both working to prevent the stitch hole from stretching. If you sew two layers of cuben together where the layers are being pulled in opposite directions (like the ridgeline of a tarp) then they are being stressed on opposite sides of the stitch hole, so each layer is really on it's own to prevent the stitch hole from enlarging.

Here's a few pics that I'm posting partially because they are pertinent to this post, but mostly just cause I'm proud of this work.

1" folded bond and then sewed:

Reinforcement patch on both sides of the cuben so it's 3x thickness and then I sewed on this loop which is what holds the door open:

Bonded stuff sack except the drawstring area. Circular bottom:

Interesting work with the Venture Tape Steve. I'm looking forward to hearing more about that.

FWIW, I have a stuff sack made of 0.33oz cuben and I've been using it for my clothes for ~6 months now and there is no sign of strain or damage on it. The 0.33oz cuben is well sewed with 2 rows of stitches to disperse the strain. For a heavy food sack I like 1.5oz cuben so I can bear bag with it without worry, but for a clothes or sleeping quilt stuff sack even 0.33oz cuben seems fine.

Re. SeamGrip, I should mention that one downside to SeamGrip is that it remains slightly sticky even when it's dry. This seems to slowly fade away, but you might find your shelter somewhat stuck together the first couple times you open it up. I think this can be addressed with some powder of some sort. Hysol on the other hand seems to be totally non-sticky once it's fully dry (+48hrs).