Performance in the wind: bonded seams vs traditional felled seams?

[Geoff Caplan]

My next project is a solo tipi shelter, which will have vertical seams around 2m long.

I’ve been wanting to try a bonded silpoly shelter for some time – it makes for a stronger, more aesthetic and more waterproof join.

I’ve been in touch with a couple of MYOGers here in Europe who have long-term experience with bonding and their feedback has been 100% positive. One of them did a lot of strength testing in the workshop before he committed, and was impressed by the results vs sewn seams. And they’ve been using the Waker Elastosil, which Roger finds is inferior to the Permatex windshield sealer. So I’m confident that the seams will be strong and durable.

My remaining doubt is around the role that seams play in storm-worthiness. A simple overlapped bonded seam will likely be somewhat less rigid than a traditional felled seam. What effect will this have on performance in the wind?

If a more rigid seam is preferable, how could this be achieved with bonding? A second strip of fabric bonded over the seam?

There was a discussion that touched on this a few years back, but it wandered off topic and never really came to a conclusion.

My instinct is that the basic overlapped bonded seam would perform just fine, and that it would be best to keep things simple. But any advice based on practical experience or engineering insight would be most welcome.

[Jon Solomon]

A friend was pretty gung ho on trying this but I never found out whether he went ahead with it not.

I’m pretty sure that you mean Wacker Elastosil. once I tried to get a hold of some in France but it was incredibly difficult for something that comes from a neighboring country.

In a previous thread, Jerry Adams explained how he uses narrow dacron tape to stiffen seams. Maybe that’s something to think about. Seam stiffness adds highly desirable structure.

Good luck with the project!

[Geoff Caplan]

Jon – you’re right, I meant to type Wacker Elastosil. I can source it here in the UK, but Roger is adamant that the Permatex is superior so I guess it’s an academic issue.

I can’t find Jerry’s posting in the search. Do you have a link? Maybe it was from before the Great Reorganisation and has joined the digital angels in the sky?

I’ve been doing some googling and I’ve had a little chat with the AIs. There seems to be a real case that reinforcing the seams would be worthwhile if it doesn’t add too much weight and bulk, and if it leaves a little elasticity to absorb wind shocks.

I’ve had an idea that goes like this:

1. There seems to be a consensus that a 2 cm overlap is about right for a bonded seam.
2. I cut strips of around 1 cm of the same fabric as the fly.
3. I bond the strip to the lower fabric, in the centre of the seam.
4. I bond the top fabric over the lower fabric and the strip.

This should:

• Add a meaningful amount of rigidity
• Be 100% compatible with the glue, so it doesn’t compromise seam strength
• Only require about 20g of fabric and no extra glue
• Add very little bulk
• Be relatively easy and practical to implement in practice.

Obviously this would be something I’d test in a mockup before committing, but I’d very much welcome any insights into potential downsides, or in better suggestions.

[Jerry Adams]

this doesn’t have much to do with bonding seams, but

I got some 1/2 inch polyester grosgrain from amazon.  To verify it’s polyester and not nylon, stretch a 6 foot length about 20 pounds, like a tent stake guyline force.  It shouldn’t stretch more than about 1 inch.  Nylon will stretch several inches.

Put that on the 4 ridges.  Sew a bunch of stitches the grosgrain to the peak reinforcement, one row of stitches along the ridge, a bunch of stitches the grosgrain to the guyline loop at the bottom.  Don’t stretch either the grosgrain or the ridge fabric relative to each other.  I do several hand stitches at the top, bottom, in between to keep them from stretching relative to each other.  Maybe the tent fabric should be stretch an inch relative to the grosgrain.

The ridges of a mid are on the bias of the panels of fabric.  It stretches a lot and distorts the fabric when it does.  A weakness of mids.  One thing you sometimes notice is on the sides, in the middle, it gets pulled a couple inches off the ground because of this.

With the grosgrain, you can put a lot of force on it and it will be rigid.  You don’t need a lot of cat cut deflection, maybe 1 inch.  The tent flaps less in the wind.  I think maybe the tent will then withstand a little higher windspeed.  And make less noise flapping.

This is an out of box idea that I haven’t heard of anyone that’s replicated, so maybe it works for me but won’t for others.

I also successfully used a 3 inch wide silpoly strip folded over to make a 1/2 inch strip.

I saw a picture of this mid in the Antarctic where it is very windy.  They had poles in all the ridges.  They are heavy.  This sort of accomplishes the same thing.  The grosgrain weighs about 3 ounces for 4 ridges

[Jerry Adams]

since this is a bonding seams thread, I am skeptical of bonding silnylon or silpoly.  I would be afraid it would fail when most needed

bonding DCF tents is fine

but it’s just an uninformed opinion of someone that hasn’t tried it

[Geoff Caplan]

Jerry –

Thanks – your experiences confirm that this is an idea worth exploring, though with bonded seams I’d have to do it differently – maybe with the method I outlined above.

After all – why make our own gear if we’re just going to replicate the commercial stuff? It’s more fun to experiment.

As for the bonding, I take my shelters into some gnarly places, so I been waiting for others to do the pioneering. Two things convince me it’s time to give it a try:

1. I’ve had contact with a couple of MYOGers in Germany who have long-term field experience. And they are both 100% enthusiastic about the results. One of them did extensive semi-scientific strain testing and the results were impressive. Bonded seams got significantly closer to the max strength of the fabric than traditional sewing. And they are lasting fine in use – no peeling or other problems after years in the field.
2. Thom Ressler at Dutchware is switching all his hammock manufacturing to bonding. He says it’s a bit slower and more expensive, but the benefits are worth it. Imagine the customer service problems he’d be facing if the start to fail! He’s betting his business on bonding.

As I say – experimenting is fun. I’m going to give it a go. The worst that can happen is that I’ll have to sew a couple of reinforcing lines along the seams – but actual users assure me that won’t be needed.

[Jerry Adams]

There’s a bpl article where they successfully bonded silnylon with silicone.  For tie-outs if i remember.

Maybe I’m a little less skeptical now

Maybe try something on scrap fabric and see what it takes to fail

A good experiment

[Jon Solomon]

Glad to see you two have connected.

Permatex is obscenely expensive in France. 19€ a tube. Don’t know what the price is in the UK. I’ve had good results using K2 silicone from Poland. https://www.k2-global.com/en/products/k2-clear-silicone-204c-85-g . Same intended application as Permatex but it is not premixed to viscosity.

[Jerry Adams]

when I’ve glued silnylon/poly, the edges roll up.  You have to put a weight on top to get a good joint

maybe you need a strip of something that’s 8 feet long to put on top of the seam and weight that down

I buy a tube of silicone and dilute with mineral spirits.  Products labeled “mineral spirits” are sometimes water based and won’t work.  For waterproofing a surface maybe 1:10 dilution, but maybe much less than that to use as an adhesive

[Geoff Caplan]

I think that the problem with curing is more an issue if you use plain silicone sealant.

The glues are formulated differently, I think. They cure much more quicky, and bond the two surfaces at a molecular level. If my understanding is right, this is a different chemical process.

My correspondents in Germany assure me that the seams made with the Elastosil don’t need to cure under pressure. After you flatten them with a roller you just need to leave them hanging for 24 hours or so without subjecting them to any stresses.

I assume the Permatex will work in the same way, though I’ll have to do my own testing.

Luckily in the UK the Permatex is only £8.95, and as you use it thinly each tube should go a long way.

[Sam Farrington]

Tried Elastosil when it was first recommended on BPL, and found it inferior for sewn seam sealing, let alone bonded seams; so have no desire to try it for bonding.  For sewn seam sealing will continue to use silicone sealer on Sil/Poly.

Realize that bonding of fabrics might be easier and simpler, but will continue to use sewn seams with lap felled flat seams, and silicone  sealer on Mettler metrosene polyester thread suited to the weight of the fabric and the needle size.  This is for MYOG and not for sale to the public, so am not concerned about bonded seam strengths.  Have never had a MYOG sewn seam fail.  Although not so with sewn seams on some marketed older tents.  But now with MYOG, that is no longer an issue.  Thank you BPL for these forums.

Roger Caffin recommended other threads on BPL; but I was unable to find it sold in smaller quantities in the USA; so have used the Mettler with no problems.  Not sure if that is still sold in the USA, though.  OK, call me a stick in the mud; but it is a bone dry mud in a tent in a storm.

[Jerry Adams]

I’ve used gutterman mara 70 thread from rsbtr without problem on silpoly and silnylon.  Polyester.

I used to use gutterman sews-all from the fabric store.  Occasionally a thread would break in a seam.

Sewing silpoly and silnylon is a bit tricky because they tend to slip relative to each other. (Faux) flat felled seams.

I have never sealed a seam in a mid because the seams are at angle and water flows downhill along the seam rather than going through the seam.

[Jerry Adams]

I’ve only had seams fail when I did something stupid, like having unreinforced guy line pull outs.

[Geoff Caplan]

Sam – what advantages do you find with the Mettler Metrosene?

I’ve been using Gutterman Tera, but it doesn’t seem to suit my classic Singer 401 whatever I try. I’ve never been quite happy with the stitch quality I’m achieving. It’s passable, but the machine is capable of better.

I was planning on trying the popular Mara that seems to be something of a standard, but neither you or Roger seem to rate it, and you both know your stuff.

The Metrosene is available here in the UK. If you were me, which would you try next?

Edit: just after I posted, I had another search for Roger’s favoured Rasant, and it turns out they finally have an outlet offering the full range in the UK.

So for tarps, mountain ponchos and the like, I’d value your advice on the choice between Mara, Metrosene and Rasant on a high quality vintage machine.

Also, your advice on a thread for 500D pack fabric would be welcome.

I realise that we’re veering OT, but I’d like to take the opportunity to pick your brains if you can spare a moment…

[Sam Farrington]

Hi Jerry,
Well, life is for learning; not to mention MYOG; but I know you knew that already.

Hi Geoff,
I asked Roger, and he agreed that the Metrosene was probably the next best after the Rasant. (Roger worked professionally with fabrics.) I’ve found that the former is very strong and works fine in the 1970’s Sears machines that I use. Also, the Sears machines could be left at the local Sears store, would be quickly fixed by Sears, and returned to the store for pick-up. When Sears tanked, I bought a couple of the best machines with the best features, but they sit in my workshop because I’ve never had to use them. Haven’t tried the Mara thread, but will see if it is sold nearby. I like to see sewing materials before buying; but in the last few years, all the good sewing machine shops seem to have gone out of business. But no problem, because I have all I need for a tent or two.

Pack fabrics are another material altogether, because they don’t don’t use much fabric, so weigh much less, and the shortcomings of Nylon fabrics are not a problem for me when using heavier pack materials. Heavier sil/nylon works fine for packs, if the pack bottom and lower sides are reinforced with light waterproof fabric. I’ll dig out the name of the pack fabric I use and let you know.

As far as my advice is concerned, I recall my Uncle who was an accomplished Judge and lawyer. When one of the great-grand kids asked to take a picture of him, he said OK, but you better hurry up – meaning that he might go at any minute. Unlike most judges, he had a great sense of humor. When I was a kid, he took me to his court to watch. All the defendants came to court in the early winter, and he would sentence them to jail to stay warm just for the winter, and be released when the weather warmed up and then be let go. His nickname was “Big Al,” because his son was Al Jr. So if you want to pick my brains, you better hurry up.
Happy Trails

[Geoff Caplan]

Thanks Sam.

Given Roger’s expertise I think I’ll try the Rasant, now I can finally get my hands on it locally.

For packs I’m a great fan of Cordura, even though it’s out of fashion these days. I have a Lowe from the early ’70s that I still use as a day sack and it’s survived many hundreds of days in the hills pretty much unscathed. And there’s a pack maker near me who sells a top spec Cordura 500 and 1000. But I’d be interested to know what thread/needle combo you’d recommend.

As for judges, my father was one of the most distinguished judges of his generation here in the UK, and my uncle was a judge too!

[Justin W]

Interesting stuff, would be great if it works well. Please update.

[Sam Farrington]

Geoff,
Yes, “Cordura” is the fabric I was thinking of. As you noted, it comes in different deniers and colors, and believe it is a rugged sil/nylon.  But I use it only for packs, not for tents that need to be lighter.

As for threads and needles, when I was making packs, the shops were open, so I’d just display the fabrics in mind, and take whatever the shop owners recommended. That saved time, with no problems. But now I may have to locate a sewing store closer to Portsmouth and Manchester NH. The solo tent currently in mind, is very sturdy, have posted about it on BPL, and find that minimizes the amount of seams by having the canopy fabric stretch over the frame.

You have me with the distinctions between folded seams. Everyone seems to have a different terminology, which is why I was more specific in the earlier post. I was referring to a seam where the edges of the panels link under each other, and are secured with two long stitch lines. It is not difficult with the use of fine pins, that are removed only just before the seam passes through the pressure foot of the machine. The sewn seam is sealed only on the outside, the goal being to keep it as flexible as possible and not gooped up with sealer.

Unfortunately, none of the sealers tested on line showed promise; so I will stick with painting seams using a small brush and one of the silicone repellents, like 3M Scotchgard or Atsko Water-Guard.  But can see now why tapes are so popular;  however, sticky tapes have a way of  separating, especially in severe weather. not to mention a problem underneath your sleeping gear.

Also, it should be noted that many of these products, even with long drying before use, often contain toxic materials. So when a tent is completed, it is left pitched outside in the back yard for at least 72 hours in fair weather, followed by subjecting it to extreme temperatures, wind, and blowing rain as soon as the opportunity arises. So far, there have been no failures due to delamination during the testing or later use in the wild.

[Geoff Caplan]

There is, in fact, a lightweight Cordura tent fabric.

The Cordura brand is owned by Invista, who bought it from DuPont. Nowadays it’s basically a rigorous set of quality standards for different fabrics. Manufacturers licence the use of the brand to reassure customers that their product meets these demanding benchmarks.

Seek Outside, who as you know are admired for their quality, use a Cordura 6.6 nylon for their shelters. ExtremTextil in Germany have something similar. Unfortunately, for use in a shelter I simply couldn’t live with their range of colours:

https://www.extremtextil.de/en/cordura-diamond-ripstop-nylon-66-silicone-coated-30den-50g-qm.html

[Jon Solomon]

Unfortunately, for use in a shelter I simply couldn’t live with their range of colours.

I just came back here to say that I have samples of several colors of this fabric and they look better in the flesh than online. Personally, I am not a big fan of olive green, but the sample looks much better than what is shown on my screen — even though my screen is color calibrated.

Niagara Blue would be good for visibility in white out conditions.

The Deep Red is beautiful if you’re into that sort of thing and the Ochre Yellow would add a lot of cheer on dreary overcast days.

But for discreet wild camping in the UK, Olive Green is probably your only choice. I would prefer something closer to Forest Green, but it’s not that bad. The coatings on the fabric, which are probably much more important than the substrate (as long as it is nylon 6.6), are superlative.

If Forest Green is non-negotiable, ET’s 30D silpoly in Forest Green is very impressive.

Have you ordered samples? It looks like ET won’t ship samples to the UK anymore. If you need help, let me know and I can send them via relay from France.

[Geoff Caplan]

Thanks Jon

Ah yes – the joys of our self-destructive Brexit! Previously simple transactions have now become complex and expensive. Nowadays it’s often easier to import from the US…

As you say, their silpoly is widely regarded as the best available for MYOG. Now that Yama, Tarptent and even MLD have made the switch I’m feeling more confident about moving away from 6.6. The sand colour is reasonably stealthy but still cheerful. I find dark green a bit too depressing on a long and wet winter’s evening!

Thanks for the offer of the relay – very kind! But I already have an arrangement, so shouldn’t need to trouble you.

[Jon Solomon]

Yes, Brexit wasn’t good on this end, either.

You probably already know this but the difference in color between the 30D silpoly in Sand and the 30D silnylon in Ochre Yellow is remarkable. Nylon holds dyes much better than polyester is what I’ve read and it certainly shows here. For cheerfulness, the Ochre Yellow wins out and it’s basically just as stealthy.

Xavier of Tipik Tentes tested the two fabrics and the difference between them weight-wise is insignificant. The real difference lies in terms of tear strength, tensile strength, and HH, with the 30D silnylon being twice as good as the 30D silpoly, which is already quite respectable and sufficient.

Good luck with your project!

[Geoff Caplan]

Jon

As you say, the silpoly is probably good enough. And there’s the point that nylon degrades faster in UV, so what we see in the lab may not be what we actually experience in the field.

I don’t think we’ll see Hillie Black Labels in silpoly, but for our less extreme uses I’m pretty confident it will do the business.

I once had a chat with a designer who has over 200 lightweight tents on his CV for many of the big brands. His take is that it’s more about proper reinforcement of the stress points than about raw fabric strength – provided you don’t go insanely light with the denier. Also, because the silpoly will hold it’s shape better when wet you won’t get so much panel spooning that will catch the wind, so you’ll need less strength in the first place…

[Jerry Adams]

nylon degradation in UV is usually not a problem

I put up my tent at end of day, and take it down the next morning so usually it doesn’t get much UV.  Sometimes I’ll leave it up all day.

I hung a piece of silnylon in full sun all summer.  At the end, it was a little faded and it seemed to rip a little easier than at the beginning – so minor UV damage.

But that was all summer.

If you had a tent up all summer at a basecamp or something, then yeah, nylon degrades some, normal use – not.

[Geoff Caplan]

On a typical hike I’ll take a day off a week, and maybe go to the beach for a few days at the end, so my shelters will get a moderate dose of UV.

As you say, probably not enough to matter much.

I know someone with a WarmLite that must be 30 years old with hundreds of days of use, and it’s still perfectly functional…

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