Shelter Project – Fabric Choice for Permatex Bonding Build

PS – the AI’s are telling me they’re seeing tests where silpoly bonding didn’t work well, despite a pure sil/sil coating. They speculate that the coating bonds differently to silpoly than to silnylon.

They are pushing me toward the silnylon on the grounds that it’s proven.

Does anyone know for sure? I can’t find the reference they are quoting and they do hallucinate at times.

Sounds like a great project!
The news that the Taiwanese supplier has stopped production of that 30D silpoly is a blow. I have a mid made out of that fabric and it is very stout.

Looking at the website now, they have what appears to be the same fabric in dark olive only. https://www.extremtextil.de/en/ripstop-polyester-tent-fabric-silicone-coated-30den-45g-sqm/72098
The specs are the same, soooo… They do mention on the product page that availability is temporary.

ICYMI, there are a couple of other choices on ET’s site that I’d recommend.

The 30D Cordura Diamond sil/sil nylon is a superlative fabric. https://www.extremtextil.de/en/cordura-diamond-ripstop-nylon-6.6-silicone-coated-30den-50g-qm/72099.OLIVGR
This would be the fabric that I would choose if my goal were to make a “bunker.” I have samples and the fabric seems amazing but I haven’t used it for a shelter yet.

There’s also the 20D sil/sil nylon, which is also made in Taiwan. https://www.extremtextil.de/en/ripstop-nylon-tent-fabric-silicone-coated-20den-36g-sqm/70777.HLLOLV
I have a mid made of this fabric and it doesn’t stretch much when wet if pitched with even tension all around. The coatings are very good and it is quite a bit lighter than the 30D Cordura.

Unfortunately, Permatex is very expensive in Europe. Good luck with your project!

I put a guyline reinforcement 4″ square.  Rsbtr silpoly.  Silicone, I think it was diluted with mineral spirits.

It seemed like it held pretty good.

But I sewed around the perimeter because I don’t trust that.  And I would never trust two pieces of a tarp glued together.  It seems like the stress of getting pulled apart by the wind would rip it apart.

I’m probably being too conservative.  It will be interesting to see how your project turns out.

I would test it with a couple pieces glued together and then try to rip it apart.

Would you put a weight on it to squeeze the two pieces together while the silicone dries?

I first use a roller to squeeze the layers together, then a weight, then I sew.

Works for me.

Cheers

Regardless of what fabric and adhesive you use, I would do some fairly rigorous testing before I trusted it on a shelter. I am curious as to why you don’t want to sew it?

yeah, better to sew also

I’m trying to build a shelter that can take a fair bit of wind.

Why bonding? I like the idea of a DCF-style shell with no needle holes. No seam sealing. No stitch elongation. No ripped fabric along the needle punctures in storm conditions. Just clean overlapped seams. And for complex cat-cut panels, I think it will simply be easier to do a good job – my sewing skills are pretty basic and the bonding can be done slowly and under full control.

I’ve been corresponding with a couple of German MYOG shelter makers who have experience with Wacker Elastosil – the E43 formulation seems to be the optimal for the job, but the E41 works too. Since I posted I’ve shifted from Permatex to the idea of the Wacker – it’s a very highly specced industrial product designed specifically for this type of bonding – not for sealing windscreens. And it’s widely available here in the UK at a decent price.

Both these contacts are encouraging me to try a purely bonded shelter. They have run extensive tests on new and weathered bonds and have long term experience in the field. They are fans of the technique. Invariably the fabric fails before the seams, even after long UV exposure.

Again, since my first post I came across a group of folks on HammockForum. They got good results with sil/sil Nylon, but sil/sil Poly was disappointing. The speculation is that coatings on the silpoly lie more on the surface, while they become more integrated with the fibre on silnylon leading to a more reliable join. This has pretty much swung me to the idea of using a 6.6 nylon, where there is solid evidence of long-term success. Unless there is someone here who can offer strong evidence of silpoly bonding working long term in the field it feels too risky to try it.

One of the pleasures of MYOG is the ability to experiments with things that would simply be uncommercial for a business. This style of bonding is FAR too slow and messy for commercial manufacture. Sewing is the norm not necessarily because it’s better but because it’s fast.

So I’m partly doing it for the challenge. Obviously, assuming my testing works out OK…

Jon, I was tempted by the diamond weave Cordura. The branding is a guarantee of quality. But the Extremtextil guys talked me out of it:

I really can’t recommend this fabric as a tent fly fabric / canopy.
Due to the diamond weave, it stretches differently than a conventional woven fabric.
The weave is also a lot denser than it needs to be for a fly fabric. We mainly sell this fabric for UL-packs, stuff sacks and so on.

I’m not saying that you can’t use it as a tent material, but this would be a better alternative:

https://www.extremtextil.de/en/ripstop-nylon-6.6-tent-fabric-silicone-coated-30den-40g-sqm/71936.HLLGRA

The “tent fabric” they recommend is specifically designed for use in shelter canopies. They’ve been offering it for years and feedback is good.

Yes – I see that they have reposted the silpoly in dark olive – it must be the end of their stock.

BUT – as I posted above, I’ve found evidence that bonding silpoly is a bit of a gamble compared to silnylon and I’m minded to play it safe.

Plus this is a partial single skin shelter. I used to have a tarp in a similar colour and found it too depressing on a long, dark, stormy night. It’s stealthy, but I really don’t think I could live with it!

Report back experience

Will you apply weight on it while it dries to make a strong joint

Very odd. The surface energy of polyester is about 42 dynes/cm2 on one web site, while nylon is about 46. That means they (should) have similar bonding tendencies. Odd.

Looking at another source, I find that untreated nylon has a surface enrgy of >46 dynes/cm2, and has good adhesion, while PE does not, and that PE has a lower surface energy than that given above: more like 30-33 dynes/cm2, and can be difficult to ‘wet’.

It may be that the silicone polymer ‘wets’ the nylon fibres more easily than the polyester fibres: that I do not know but it seems likely from the above. Or it may be that the coating process for the two fabrics is a bit different, or maybe the weaves are sufficiently different that the polymer diffuses differently. Unknown.

What I do know is that experiment trumps theory every time.

Wacker incidentally is a good and major player in the polymer arena.

HTH, cheers

Geoff,

That’s an intriguing response from ET. I had been thinking that it was precisely those qualities that would make the Cordura Diamond silnylon a top choice. I’m sure that you would have noticed this detail from the product description:

Thanks to the fiber property and weave density, the Silnylon stretches much less than our silicone coated tent fabrics and it is much more resistant on punctual seam stresses.

On the face of it, “stretches much less” ought to be a huge plus for a tent fly, while “much less than our silicone coated tent fabrics” sounds like a huge W. Plus, the product page does mention “tarp/tent” among the range of applications. I mean, I’m sure the folks at ET know their stuff, but I’d still be tempted to try the Cordura, especially for a non-woven bonded application.

I was aware of the successful use of the Wacker Elastosil products on the German forum and tried to source some from France several years ago but it was hideously expensive to get shipped across the Rhine. Probably should have tried contacting users in Germany directly for assistance.

As concerns the last remaining stock of 30D silpoly, I agree with you about the Dark Olive color. I had a mid in that color and didn’t like it at all. The Light Olive color of the 20D silnylon from ET, though, is perfect for 3 seasons in Western Europe. It blends in extremely well to the foliage and is very cheery inside. However, now with the extreme heat becoming a regular occurrence, that Light Olive doesn’t blend as well into the frequently parched, yellowed out landscape. Unexpectedly, the Ochre Yellow color of the 30D Cordura Sil would fit in well to the new “scorched earth” theme that has become common in Western European mountains and it would be very cheery to boot. Don’t know if you’re observing the same parched landscape in the UK?

As for the 30D silnylon they recommend, I’d personally prefer the Leaf Green color over the Light Grey.

Geoff, wouldn’t the higher density and lower elasticity of the Cordura sil be an advantage for a bonding application?

Jerry

My German contacts report good results without pressure – which will greatly ease the process. If anything, applying pressure, under glass for example, would inhibit access to the moisture that drives the curing process.

The Wacker data sheet doesn’t make any mention of pressure. So far as I can tell, you should:

1) Clean the contact area with surgical spirit to get rid of any grease

2) Clean it with heptane to remove any bloom off the coating

3) Coat one side of the seam evenly an moderately thinly, without going to extremes

4) Apply the other side to the Elastosil and roll seam gently from inside to edge with a silicone wallpaper roller to ensure even contact and drive out bubbles.

5) Allow to cure with no shear strain at all on the seam for 24-48 hours. Leave longer before applying any weight just to be safe.

If anyone has any proven improvements on these steps please post and share.

Of course I’ll test to check results.

Here is the advice from the official data sheet:

Processing

ELASTOSIL® E43 N TRANSPARENT is a ready-to-use, one-part silicone rubber which starts curing when exposed to air moisture.

As RTV-1 silicones require humidity for curing, free access of air moisture to the silicone rubber is essential. Additionally, the vulcanization time of ELASTOSIL® E43 N TRANSPARENT can be greatly reduced by increasing the level of air’s relative
humidity.

Please note that, unlike the initial skin formation, the total curing rate of RTV-1 silicones is limited by moisture’s diffusion speed in silicone rubber. As increasing the curing temperature has just a minor effect both on the skin forming time and the curing speed, ELASTOSIL® E43 N TRANSPARENT typically is vulcanized at room temperature. Heat curing is recommended only for applications where the silicone rubber is applied as a thin film (thickness less than 0.5 mm), because otherwise blistering is likely to occur due to the quick release of acetic acid.

After completion of the vulcanization the silicone elastomer may continuously be exposed to constantly changing climatic conditions, UV radiation and high temperature without damage.

Cured ELASTOSIL® E43 N TRANSPARENT usually shows good primerless adhesion to many substrates, e.g. glass, ceramics, metals, plastics and powder coatings.

Detailed information about the processing of RTV-1 silicones is given in our brochure

“ROOM TEMPERATURE VULCANIZING (RTV) SILICONES – MATERIAL AND PROCESSING GUIDELINES”.

We recommend running preliminary tests to optimize conditions for the particular application.

Removal:

If removal of the silicone from machines or dispensing equipment is necessary, white spirit or similar nonpolar solvents are recommended. However, cleaning ideally should take place before the silicone rubber is fully vulcanized. Cured silicone needs to be rubbed off or removed mechanically, if necessary in combination with a swelling agent (solvent) or a chemical silicone remover.

Living in the English Lake District, I don’t think access to moisture will be much of a problem!

Interesting.  It would be difficult to apply weight on a long seam

I’ve always used weight but just for small patches.  Not so much weight to squeeze out the silicone.

I think the Elastosil RTV-1 formulation is a different chemistry. It’s a specialised industrial bonding agent – probably works in a different way from a silicone patch bond.

Most people seem to think that pressure is needed for silicone or Permatex bonding.

In theory the Elastosil should be insanely strong. It’s advertised as 12.5 N/mm. I’d be using a conservative 4cm or 5cm overlap, which should be far stronger than the underlying fabric.

I just use silicone + mineral spirits, which may require a weight to keep the two sides together

Geoff, I’ll offer my experience for what it’s worth.

About a year ago I finished my tunnel tent prototype (1 person, 2 stakes, 2 or 3 poles, 27 sq ft; someday I’ll do a detailed writeup on the design and build to see if Ryan wants to publish it). The fabric is the RSBTR 30d sil/sil MTN nylon 6.6, which I suppose is comparable to the ExtremTextil 30d silnylon (or the same?). I don’t much mind the stretch-when-wet aspect of silnylon, especially in this design, in which I can retighten the entire tent from a single point without leaving my bed. This fabric seems fine and easy to work with. It’s been through some heavy rains with no problems. My one complaint is something you will probably love: that it’s too bright inside—it’s like a Fresnel lense, magnifying the sun (I need something with dark, dense shade).

I did also consider the 20d sil/sil nylon mentioned from ExtremTextil. I bought samples and tested seams, concerned about reports of “loose weave”. Yes, it does seem a bit loose, and stress tests with weights on a seam did show some needle holes opening up. I believe that in practice this is unlikely to be a problem, that good sealant will prevent leakage, and I think it unlikely the fabric would reach its strength limits even in a strong wind. And the fabric is crazy waterproof, as tests have shown, and it’s very opaque for its weight. However, in the end I chose the RSBTR 30d fabric because I wanted something with presumed longer durability and because the ExtremTextil 20d is so thin and soft it feels like it “has no structure” and is harder to work with (e.g., it won’t take any kind of fold).

I used a lot of bonding to build the tent, mostly for positioning but also in lieu of stitching in two critical instances. The most critical is how I bonded stair-step reinforcing patches in the high-tension cone ends of the tent—in this 2-stake design, almost all of the tension of the tent comes through these two end cones, so they must be failproof. I have not seen any delamination or separation of fabric edges here or on any of the bonded pieces of the tent. Here’s how I did it:
• For bonding in general, I first considered whether the size of bond would be appropriate to the load it might receive and the angle the force would be applied (it is possible to rip off a bonded piece in certain directions). When in doubt, sew in addition, or instead. You will have to guess and test what is an appropriate width for your bonded seams. Maybe the Elastosil makes a stronger bond than Permatex?
• I used high-quality sil/sil nylon and worked only with new, clean material. I did not do any cleaning or other surface prep.
• I used Permatex Windshield and Glass Sealant, 81730.
• I spread the sealant in thin, wide loops on one surface to be bonded, and lightly spread it out until it contacted the whole surface.
• I positioned the second surface to be bonded, then squeegeed outward from the center with a plastic putty knife, to push out excess sealant and eliminate bubbles. Wipe away excess.
• I did another round of squeegeeing all over. My goal was to leave a very thin layer of sealant—just a few layers of molecules–but not to eliminate as much as possible. It is possible to take away too much and have a poor bond.
• I weighted the whole area with flat, polished blocks of stone (I’m a stone sculptor, so I always have polished bases laying around). Glass or tile modestly weighted would serve similarly. Or books, if necessary.

I don’t feel the same as you about maybe depriving the sealant of air in this early stage. I want to get it flat and keep it flat so the layers adhere tightly. Once that part is secure, there will be ample curing time once the blocks are removed. The narrow pieces you will be using will over time allow ample air and moisture for an eventual cure no matter what you do. (Or maybe the Elasosil is different?)

The wholly-bonded tent sounds like an interesting experiment (one that does add a bit of weight) but one motivating factor you mentioned here and some earlier post you might reconsider: wanting to eliminate needle holes. If a big part of that concern is about leakage, I’ll say this: after using a home-sealed Warmlite silnylon tent for 20 years and building three silnylon tents of my own over the space of 18 years, I can confidently say that if you seal it properly once—with only one coat—you will never need to seal it again, and it will never leak. My seams have never leaked and I have never ever seen silicone sealant peeling the way we all used to see peeling with urethane. These sil fabrics and silicone sealants are so in love they just really glom on to each other. In the early days I mixed my own with stinky solvents, and have tried Seam Grip, but now the Permatex is so very superior and easy. It doesn’t smell like anything, it’s so easy to apply precisely right out of the tube with a small hole, and you can just stick a wire in the hole and the sealant will still be good months later. Sew with confidence, seal carefully once, sleep well.

ExtremTextil 20d under stress opened some needle holes

Spreading stress over 4 layers of fabric (maybe overkill?)

Two-stake tent, with three poles

With two poles

Hi Moab

Very nice.
I am afraid I was never game to try a single stake at the end: I always went for two. No matter.

Cheers