No-sew tarp seams with McNett Seam Grip – are their claims credible??

[Geoff Caplan]

I noticed that on the web page for their Seam Grip adhesive, McNett claim:

“We have had users make tents and tarps without stitching by simply bonding all the seams with Seam Grip. The results have been incredibly strong, waterproof shelters.”

If this really worked for, say, a tarp ridge-line, it would have obvious advantages, as sewing must weaken the fabric somewhat, and it is a source of leaks.

But I’m pretty skeptical, as no reputable manufacturer is doing this commercially, so far as I’m aware. But perhaps this is for commercial rather than technical reasons?

Does anyone have experience of using this technique for a tarp or tent? Has it proved durable? How specifically did you make the seams?

My shelters get heavy use and are sometimes exposed to big wind loads, and I’d be using RSBTR Silpoly PU.

I’ve asked McNett for more info, and will post anything of interest that comes back.

[Jerry Adams]

would seam grip bond to silpoly PU?

if you had to use silicone, I don’t think that’s strong enough

if you seam grip a lap seam and pull sideways on it that might work, it’s pretty strong.

[Roger Caffin]

The PU version of conventional Seam Grip will bond to PU coating fine, but NOT to the silicone coating.
I did see mention of a silicone version of Seam Grip – if true that would bond to the silicone coating well, and to the PU coating only medium.

Cheers

[William N]

I’ve attached webbing to make a ground cloth that would hold my BigAgnes tent poles. I used ShoeGoo, so I would think McNett would work. Surface area of contact is the critical factor, and if the material stretches more than the sealant, it could work loose over time.

What I also know is that 100% silicone caulking smells different from McNett, but is about 1/6 the price and works exactly the same. (thin with mineral spirits, paint thinner…)  Also non-silicone Seam Grip doesn’t work on Silnylon, but silicone sealer (theirs or GE from HomeDepot) works on everything.

What’s really needed is a way to lay down a consistent width and depth of sealant.

[Jim Colten]

No-sew silnylon tarps are possible using GE Silicone II glue, I do not know about Seam Grip.  This 8 year old tarp is almost no-sew … the only sewing was to attach a zipper the beak.  It is an adaptation of the Jay Hamm tarp published in BPL’s early years.

 

[Patrick P]

Interesting. Their may be lots of factors why manufacturers are not just gluing. Maybe a polymer chemist could chime in.

Here is some basic testing.

https://m.youtube.com/watch?v=_5yGxdJveZk

[Eric B]

I have no direct experience wiht this, but I would imagine that there’s a throughput issue with bonding seams commercially. It would impose serious space and time constraints if you had to leave a tent or tarp pitched for, say, 12 hours before it could be packaged and shipped.

[Iago Vazquez]

@Jim: Was this the glue that you used? There seems to be a type I and type II available. None of them discusses fabrics, which doesn’t mean it won’t work… Thank you!

@Patrick: Thank you for sharing that video. That looks great!

[Jim Colten]

@Iago:  Yes, that is what I used (type II)

“type I” is sold as caulk … I am not familiar with it other than for installing exterior doors and windows (none of which have found their way into my pack, he-he)

[Jim Colten]

Here are the MSDS sheets for both types.  They appear to NOT be identical:
Type I

Type II

[Iago Vazquez]

@Jim Thank you so much!

[Sam Farrington]

I tested Seamgrip on polyurethane (PU) coated fabrics because I wanted to install large reinforcement patches at stress points without a lot of sewing that would only weaken the fabric further.

The resulting bonds were very strong, and could not be peeled away. And it may be that a two part low viscosity PU adhesive, such as the Loctite products previously recommended here for use on Cuben fabrics, might do even better, bonding the reinforcement patches with an even thinner and therefore lighter and more flexible coat. As earlier reported, had no luck thinning Seamgrip with products suggested here, as the bonds were quite weak, not really bonds at all.

However, as Roger suggests, only the PU coatings are being bonded, not the threads of the fabric. So the bond is only as strong as: 1-the strength of the fabric, and 2-the strength of the bond between the fabric and the original PU coating done by the manufacturer. Still, I think the bonds I observed were very strong and would work well with high quality nylon with a high quality PU coating. One fabric I used was from a StoS Escapist tarp that was tested and reported on here by Richard Nisley.

I only see relevance of silicone to the OP’s inquiry in that many very light nylons are now coated with silicone on one side, and polyurethane on the other. With these fabrics, only the PU coated sides could be bonded with PU adhesive, and identifying which side is which is not always an easy call. Sometimes it is necessary to use dabs of PU and SIL adhesive on the fabric to be sure. I understand that some fabrics are coated with a blend of SIL and PU, but have not seen any personally, so have not been able to test bond them.

Surely, if shaped Cuben tarps can be successfully made with adhesive bonding, as has been often reported here, then it should be doable with PU coated woven fabrics. The threads here on this subject are legion, so won’t try to report them all here. PU is some sticky stuff, and some study and practice with the joinery should be necessary.

However, I would not try to make a tent this way, as too many seams are involved. But intend to bond reinforcement patches this way, and then sew only over the hemmed edges, knowing that the raw edges of the patches further inland on the fabric will hold without peeling. A basic pyramid tarp should also be possible if you can get the bond right on the seam line set for a catenary cut.

[William N]

I use the HomeDepot GE 100% Silicone. It works as good or better than that small expensive Seamseal, and it sticks to everything (you never have to worry if you’ve got the right one).  It’s dirt cheap compared to the expensive stuff, and I think it’s fresher and less viscous (flows better).  I would say it’s the same stuff, but it smells different. The recommendations for thinning it is to use Mineral spirits. Paint thinner works just as well. You can also buy small packages of the little brushes in the plumbing department near the copper pipe soldering flux. Something like 6 for a $1. I’ve used this stuff for years, it holds up well on around plumbing fixtures, the bathtub, as well as on my gear.

But then there’s the other issue. Why glue what you can sew? When I make a silnylon fly, I sew the edge seam but I don’t seal it. What’s it going to leak on?

At the peak seam, grosgrain loops in the middle, these I seal, but only on the outside, and only the stitching and anything next to the stitching.

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