Bonding silnylon/silpoly seams – flexible or rigid seams?

[Stumphges]

As Roger Caffin has pointed out, 3M makes various siloxane adhesives that might work to bond, rather than sew, the seams of a silnylon or silpoly shelter.

3M make both double-sided siloxane tape with 1 mil polyester film in the center (https://www.amazon.com/3M-96042-NAT160-Scotch-Silicone/dp/B0167E88C4/ref=dp_fod_1?pd_rd_i=B0167E88C4&psc=1) and transfer tapes that are only adhesive.

I would think that the polyester film of the double-sided tape above would make for a stiffer seam, but is that what’s wanted? Would it be better, from a structural perspective, for the seam to be bonded only with flexible siloxane adhesive that might allow the seam to stretch more?

I’m thinking stiffer is better, but maybe the question is better framed as – which would better replicate a sewn seam?

[Eric Blanche]

I remember one of our bpl posters who suggested a more stiff seam was worthwhile. If I remember correctly, his conclusions were based on the examples from the four ridgeline seams on a rectangular mid reinforced with grosgrain.

[Sam Farrington]

If you have a source of transfer tape, please include a link also.  I spent many weeks hunting for a sil transfer tape, found one, ordered it, and then they cancelled the order without explanation.  Guess is they misadvertised it.  Not worth the time.

Even with silpoly instead of silnylon, I would want the tent canopy to be as elastic as possible, in order to keep the canopy taut and distribute forces.  This produces a more durable and wind resistant tent.  Do not think that using the Amazon tape will do that; rather it will make seams more stiff.  That might be desirable for a simple tarp, but for a simple dome shape, where I want the fabric to flex on the bias in order to remain taut, not so much.

So while it is more work, will stick to the Permatex that Roger uses for bonding.  I’ve tried it with bonding patches with clamps and 72 hour waits, and it makes a strong bond for reinforcement patches that is flexible and hopefully will not separate at the edges.  For the long seams, I’ll have them run along the fabric grain as much as possible, as that has much less elasticity anyway, and should not interfere with bias flex.

The problem is with vestibules that tend to be triangular, so have at least one seam edge that runs partially on a bias to the grain.  From posts by Jerry and others, am thinking about making seams on the bias equally so, and also with a cat-cut, and maybe with a door zipper, in the hope this will avoid wrinkling.

[Stumphges]

Sam, I just spent a little time looking for 3M 91022 silixone transfer tape and could only find it in bulk. Very pricy.

My thinking is in terms of pyramid tents with an even number of sides/ridelines. So half will be seams mating selvedge/selvedge edges and half bias/bias. It’s the bias/bias rideline seams I’m wondering about.

(I know that some people make pyramids with the ridgline seams selvedge/bias, but the ones I have are as above.)

I’m not sure the 1 mil polyester film in the double-sided siloxane tape linked above would actually contribute much structure. It might stretch out during first use and then be moot.

In truth, I’m trying to avoid learning to sew and tackling the flat-felled seam learning curve. Encouraged by some recent MYOG bonded DCF tent success stories documented on this forum recently, I was thinking I would learn to bond DCF. But the bias instability of DCF is a turn off, and I’m now wondering if bonding a silicone-coated fabric might be the way to go, for me.

Sam, if you’re sewing a bias/bias seam in silnylon, does your sewing technique constrain the stretch of the fabric along that seam, or is it meant to allow the fabric on the seam to stretch?

[Stumphges]

I found this site yesterday. German fellow bonded a silnylon hex tent and shows his technique using Elastosil, which I think is very similar to Permatex: http://www.pluennenkreuzer.de/001_Landgaenger/603_Silnylon_kleben/silkleben_01.html

To my eye, using a transfer tape would be a lot easier than applying glue to a long seam, although his rig looks pretty effective.

He also has a nice article about cat cuts and how they help to tension panels: http://www.pluennenkreuzer.de/001_Landgaenger/603_Silnylon_kleben/silkleben_01.html

Quite good run though google translate.

[Sam Farrington]

Stumphges,

Thanks for the link to the German tent builder.  You are right, the translation was much better than I’m used to.   Will spend more time with the link, thinking about bias-to-bias seams.  Do know from Jerry that the degree of bias should be the same for both panels being joined.

Being a sewer (no pun intended) of sorts, no worries about bonding tapes; but do expect that when the one mil plastic on the double-sided tape is coupled with adhesive on both sides of the tape,  plus the two layers of fabric, it’s going to add stiffness.  As said earlier, that may not matter much with a tarp ridgeline.  But expect that with either sewing or bonding it will create wrinkles emanating along the bias seam.  Need to ponder more, but will study the German guy’s article, and look carefully at the bias/bias seam on my Goondie, as it does pitch quite tautly in dry weather, although is PU, not sil coated.  Because it is nylon, though, it has a fair amount of wrinkling when wet.  So will try the Silpoly.

Tested the Elastosil and found it did not compare with the Permatex Roger uses, if his instructions for bonding are followed.  Roger describes his bonds as close to molecular.  The patches would pull apart for me, though; but it took a lot of force, more than I’ve seen with any other sil bonding products. Used GE sil glue for reinforcement patches on a sil prototype, and found that after a while, there was separation  along the lines of force in the patches.

Am comfortable with sewing, so that with a sealant (probably just more Permatex) am not worried about leaks.  None of my modded silnylon tents leaked in the field.  The problem has been that in wet weather, the expansion of the nylon eliminates the ability of the canopy to add support to the tent.  That may not be an issue with a pyramind, but when attempting to use fabric panels to reinforce a self-supportng structure, a taut canopy is needed.  As posted before, setting up a prototype using a 30D first quality silnylon from Quest totally robbed the structure of its stability and tautness when it was moved from a dry workshop to the outside in wet weather.  So no thoughts about using the silnylon.  Have a sample of Thru-Hiker 6.6 30D silnyon that the owner sent years ago, so could test that for sag in bad weather, or just use some of the RBTR 30D 6.6 silnylon that was bought for a floor.  Or may just use some of the Korean silnylon bought from Judy Gross, as that has worked well for the floor on the Goondie mod.  I use plastic embroidery loops, about 11″ in dia., to tighten the fabrics, and see what happens with exposure to bad weather.  Nylon always fails, but is strong, durable and ideal for floors.

Good luck with your bonding.  Hope it works OK.

[Jerry Adams]

“Do know from Jerry that the degree of bias should be the same for both panels being joined.”

I think I’ve changed my mind about that.

I have two “ridges” on my half mid with a vestibule that have one panel on the bias and the other panel on the grain and it works fine.  In fact, it works sort of like putting a stiff strip on a ridge where both panels are on the bias.  The panel on the grain stiffens the panel on the bias.  You don’t need to add a stiffening strip to the seam.

Hmmm… I suppose one could design a mid where every ridge has one panel on bias, one on grain.  Probably not : )

When you sew a panel on the grain to a panel on the bias, the bias panel tends to stretch as you sew it so it no longer lines up when you’re at the end of the seam.

[Stumphges]

Jerry, interesting, the German fellow who bonded the hexagonal pyramid tent (linked above), seems fairly adamant that ridgelines should be bonded selvedge/bias. As long as you have an even number of panels/ridges, you can do this on all ridges:)

My favorite pyramids, however, have the traditional, alternating bias/bias, selvedge/selvedge ridges. The selvedge/selvedge obviously at the door, and alternating from there. This works very well and results in a wrinkle-free pitch, but as I mentioned in that other thread, the bias/bias ridgelines (and the panel fabric just adjacent to the ridgeline) is not as stiff against deformation as the selvedge/selvedge ridgelines are.

But this construction style seems to allow for maximum tension applied to the bias, such that so much bias stretch is taken out of the panels in pitching that they don’t sag when wet. And I should clarify – this only seems to work, from what I’ve seen – with radially symmetrical mids – and I’ve only observed it with a regular octagon mid with cat cut ridges and hems. (See link above about cat cut hems).

And its because of this design alone that I’m thinking of using silnylon – I’d like to replicate it in a smaller size with bonded seams.

If I were trying to build any other kind of tent, I would be looking for the best and lightest silpoly. Your testing, Sam, appears to confirm that silnylon sag is an unsolvable problem in domes.

I’ve been collecting swatches and comparing them. There are lots of very nice sil/silnylons out there now. The silpoly that feels the most impressive to me is the 30d, 45 gsm stuff from ExtremTextil. Getting pretty heavy, but this feels, looks and behaves like high quality sil. Getting too heavy probably, but interesting fabric.

[Sam Farrington]

“Your testing, Sam, appears to confirm that silnylon sag is an unsolvable problem in domes.”

Yes, but the domes have pole structures that help to keep them taut, or at least not sagging against the occupant; and with some added cat-cuts, they are habitable.  There was an old thread from “Hang-em High” on BPL that illustrated this when compared to an A-frame tent or tarp.  Although (pyra)mids may do better than domes with wind deflection, I’m not sure they do much better with silylon in terms of keeping the structure stable and taut in storms.  And if one stake goes ….

Would think that for a pyramid with equal size and shape panels on each side, the panels would be identical triangles, or equalateral.  So it would be easy to cut them so the bottom hem runs along the grain, and along a partial bias on the sides which would have the same diagonal angle of bias on the panels to be joined.  The cutting lines would look like two giant saw teeth joined at the edges to be cut, with the lines curved slightly inward for a cat-cut.  That seems more like what you describe. It also makes efficient use of fabric.

Certainly a panel cut on a bias at its edge could be joined to an edge cut along the fabric grain, and the bias edge could be pulled tighter during the sewing or bonding; but don’t think this is really needed if the triangles are equalateral.  Am not as sure as Jerry and Hartmut of their approach.

But if the triangles are not equalateral, the seams on bias panels appear to have different angles of bias.  Cat-cuts help with this, but am not sure a mid canopy will be as taut.  There was a recent thread that went into mid designs at length, and might be helpful.   A simple answer would be to make the mids with square or equal sided footprints, leaving most of one side for vestibule storage.  This has to be done anyway to keep water from pouring into the living space when the door is opened.

For a common design that has an A-frame shape with beaks on the ends, the simplest approach would be to make the seam lines joining an A-Frame to beaks on the fabric grain of both panels.  The beaks would not be equalateral, but if they meet at the tent’s center would do so with the same angles on the bias cut; that is, the beaks would be of identical size with identical angles on the bias lines.  With some thought, the vestibules could be sized so the beaks are right triangles, and their bottoms cut and hemmed on the grain. (The selvedge line and the line perpendicular to it both share the same characteristic of having zero bias stretch.)

This leaves the question of how to keep the large rectangles on each side of an A-frame taut, even with poly that does not sag when wet like nylon.  One approach is to design the pole structure to run along the bias lines as I’ve often illustrated with a prototype, where the bias stretch is absorbed by the poles:

This has the added advantage of using the bias stretch to create more space inside the tent.  As previously noted, I’ve also found that bias stretch does not keep the nylon side panels taut when soaked, but am hoping silpoly, which also stretches on the bias, albeit less than nylon, will address this.  Although the increased space under the A-Frame may be less with poly, it still beats a plain A-frame with the sides unsupported.  Note that the ridge of the tent naturally assumes a cat-cut, so the only cat-cuts are where the beaks join at the front and rear of the tent.  The leading edges of the A-Frame maintain taut straight edges, keeping the seams from sagging where the sides are joined to the beaks.  Still, the devil is in the details, and as Roger once noted, the biggest question is how to quickly install the poles under the canopy, an issue that has taken the most thought.

Have often thought of applying some of the above to mids, so that instead of caving the walls inward at their cat-cuts, the tent is supported by one flexible pole that, similar to one of the arced poles shown above, weighs under 4 oz, and causes two sides of the mid to project outward.   But expect that the demand for tents supported by trekking poles will continue to prevail.  My one combo carbon-alloy trekking pole weighs 7.5 oz, and is 53.5″ fully extended.  Hmmm.

[Jerry Adams]

My center pole is 61 inch.  Sort of tall to create more headroom inside so I can sit in the rain.

I have a 0.44 inch pole that weighs 4.4 ounces for winds less than 15 MPH or so.

and a 0.625 inch pole that weighs 7.5 ounces.  I’ve probably done 40 MPH winds?

I can think of one trip where it was unexpectedly windy, with my lightweight poles.  Tent was flapping so a stake pulled out and the tent collapsed on me, so I found a branch that worked better.  I have to remember to take heavy pole more often.  The 0.44 inch poles are marginal, but I like saving 3 ounces and they work fine on maybe 90% of my trips.

I think that if you have more than one pole, their weight will be a few ounces more.  This is an advantage to having a mid.  If you curve a pole, like in a tunnel tent, it takes out some of the strength – if it then curves some more it can fail.  Trekking poles are good, because you’re carrying them anyway, so they effectively add no weight, but they’re sort of short.  Dan’s tent overcomes that though, because there are two poles with a ridge between where your headroom is – don’t need as long a pole.

My tent is a half mid with a triangle vestibule on the other side.  So, I have two ridges that are bias to bias with a stiffening strip.  Two ridges are bias to selvedge which works fine with no stiffener.  And one ridge is bias to zipper which is stiff enough by itself.  Also a seam that’s selvedge to selvedge which works fine by itself.

I am skeptical of the idea that stretching a nylon bias to bias ridge is a solution to the problem of nylon stretching more when it gets wet.  If you put the maximum amount of tension on the ridge it will flap less in the wind, which I think will tolerate higher wind speeds.  If it then gets wet and stretches, it will no longer be the maximum amount of tension so it will start flapping more, you have to go out and tighten it.

I think nylon and poly stretch about the same.  It depends on how they weave the fabric.  The advantage to poly is that the stretch doesn’t change when it gets wet or cold as much as nylon.  And the disadvantage is that it’s a little weaker.

[Stumphges]

I found, and have now lost, an old Caffin post where he expresses a preference for 91022 transfer tape over the double-sided tape I linked to upthread, because a) the film in the center of the double-sided tape is still and might conflict with the fabric’s stretch, and b) that this might cause adhesion failure, which makes sense.

Unfortunately, that leaves us nowhere with respect to supply of 3M 91022 siloxane transfer tape. I found a 3M info sheet that said both tapes were good for 1 year after manufacturer. This may explain why suppliers a) don’t actually have the stuff in stock when they appears to, and b) why one can’t find a single roll of the stuff. Nobody actually has this perishable product on their shelves and so every order is a special order and therefore has minimum order size of one case. Also makes me think that the double-sided tape on Amazon might be single rolls of stuff that’s gone off.

Vaude is offering two different no-seam silnylon tent constructions – one bonded and the other taped. I would think they are using 91022 for the latter construction. Good for them.

Sam, I don’t use trekking poles normally, so would actually prefer a dome tent. They are just so easy to set up, flip over to clean floor, move about, etc. But the polesets get quite heavy, so the storm-resistant designs (e.g. Kuiu Mountain Star) are over 3 pounds for 2p and the UL stuff have weak pole designs and iffy ultra-thin sil/PU fabrics and don’t look storm-worthy. As I’ve mentioned to you before, though, the perfect tent for me would be a dome with an inner that inhabited the standard rectangle plus one of the vestibules. But no one makes such a thing.

Your pole design is, I think, the way to go. That’s the general shape of Kuiu’s pole setup and the Mountain Star looks very solid, despite not having the fly stretched over the top, which could only make it stronger. Getting more headroom out of the deal is brilliant.  What would happen with the design you’ve pictured if you just attached vestibules with one ridgline coming off the ridge of the A-Frame, like a TT Rainbow but with two poles rather than one running down the principle ridge?

And speaking of Rainbows, I think that design is about as close as we see to your conception of a pyramid tent supported by a single arched pole. In many ways, that’s just what the Rainbow is. I’ve never quite understood why the Rainbow is considered marginal for high-winds while the Phreeranger has a decent reputation in Scotland, where the basic design scheme seems to have originated.

You raise a very good point about cat cuts – they are necessary to pull the bias out of panels in a pyramid design – but they do make the panels concave, which is fundamentally NOT what we want when meeting with wind. Much better to have poles presenting the panels as convex to the wind.

In general, using arched poles to tension the bias of woven fabrics is very good architecture, and this actaully explains why doing the same with DCF has continually been met with failure. In Podcast #2, Ryan mentions the difficulty tent makers have had cutting and sewing DCF panels for arched, domed tents, and attributes this to a lack of forgiveness due to lack of stretch. The DSM rep objects, pointing out that DCF does stretch – on the bias. But that stretch is inelastic, and designing a shelter to stretch DCF panels in those dimensions around a dome will result in plastic deformation, saggy panels, untensioned polesets and miserable, lumpen failure.

[Sam Farrington]

Jerry,
Touche, I overlooked the obvious, a simple extension tube on the Trekking Pole. On my pole that would mean removing the rubber cap over the tip, and trimming a short tube to fit over the pole tip. The weight of the extension would be negligible, I think, especially if made of carbon tubing.

Stumphges,
As noted above, the hunt for sil transfer tape became a waste of time, which is in short supply. Regarding the Rainbow and its ancestors, I do intend to add a transverse ridge pole. Not just to add stability, as the design is already self supporting; but to allow the vestibule beaks to attach to a solid inner made with DWR that is breathable, so will shed water long enough for the pitch; and the fly thus smaller, so it can be a long but thinner rectangle that is easier to install in winds. Most of the ‘domes’ have huge flies that include the vestibules. Roger posted a pic of a guy chasing one of these flies over hill and dale when trying to pitch in a blow. The narrower fly may add ventilation also.

Agree about the cat-cuts on a mid reducing space inside, and the utility of the phreeranger concept. It is not self-supporting, however, whether Henry thinks it is or not. To begin with, neither of us carries two trek-poles. Suggest that a better approach would be a transverse tunnel-side entry, about which there was a popular thread here a couple years ago. As you suggest, adding even a single long arched pole does add weight. Carbon fiber from the sturdiest shafts from Gold Tip does get this under 4 oz, though. The one flexible pole would be more susceptible to high winds, though., making a second and smaller arch pole desirable to get the most stability from a tunnel design.

Also agree with your concerns about DCF; but no question, woven fabric is heavier, and flexible poles just add to that. But although these items are not negligible, a self-supporting tent can be more stable in the wind, reducing the amount of stakes needed in lower winds, and using stakes already in the design to attach guylines in higher winds. Am also thinking of using one of the vestibules to extend the floor, as done with a Goondie posted here, and this would allow a narrower and lighter canopy. Using lighter fittings, and less of them, also helps considerably with weight. Since the floor can be silnylon, this can be a lower denier. The lightest Kerlon 1000 tarp appears, around 0.7 oz/sq/yd (check math), would make a much lighter floor than planned, but would cost $180, quite a lot just to take a look. A DCF floor would receive a lot of abrasion, though. With enough misc. reductions, the weight could be brought much closer to that of a DCF tent.

[Sam Farrington]

Just read T Hoosier’s 2016 thread about his DCF tarp that he brought forward to try and buy it back.  No wonder, only around 12 oz, and tons of space.  Am reading a book about Winston Churchhill, and will need his grit to resist the pull of DCF.  Although T’s workmanship with DCF is phenomenal, and don’t know if I could ever come close to it.

The weather is a bit different in Colorado, however.  The altitudes are high and the downpours can also be phenomenal; hence the pull of a double wall that is bomb proof.  But would think it would have to close to 20 ounces to justify the weight.  Were it not for silpoly, the next tent would be DCF, though.

Just finished a 72 hour bonding test of J-B Weld sil sealant and adhesive.  Not quite as good as Permatex, but noticeably better than Elastosil.

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