Polycryo Strength Analysis

[Kodiak Firesmith]

I'm kind of curious if anyone has tried tyvek tape as well, I have a big roll of that coming soon so I'll play with it.

[Michael Ray]

I don't think so but let us know how it goes.

For an emergency shelter as you're intending, making a ripstop version is a waste of time and will greatly increase the weight. I personally wouldn't do it anyway.

[David Gardner]

Kodiak,

There's at least one other long BPL thread on polycryo shelters:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=59450

On page 9 Ryan "Rudy" Oury (ohdogg79) uses packing tape in a diagonal/radial pattern for reinforcement across stress paths. I saw his tarp at GGG #6 and it definitely provided the desired reinforcement, but there was some concern about the long-term durability and adhesion of the packing tape. His pattern was different than your ripstop grid concept, but it would perform a similar function in terms of limiting a tear and keeping it from becoming an unrepairable catastrophic failure, in addition to the strategic reinforcements making a tear less likely to begin with.

Instead of packing tape you could slice one of the above-mentioned weather resistant tapes down to 5/8" strips (1/3 of the typical 1.88" tape width, so no waste) using the utility-blade-screwed-to-a-piece-of-wood technique.

Making a reinforcement pattern using the double-sided tape that comes with the kits pressed between two complete sheets of polycryo would be *very* interesting. Probably tricky to fabricate but if it could be done I'll bet two layers of .7 mil assembled that way would be stronger and more tear resistant than one layer of 1.5 mil. And you could still add the 5/8" tape strips on top of that, if you wanted ultimate reinforcement. I wish I had time to try that myself right now, since there never seems to be a shortage of the .7 mil kits at many places instead of Walmart.

I called Duck a few months ago trying to track down some other retailers for the 1.5 mil, but they just told me to keep checking Walmart because it would be back in stock eventually. Give it a shot though, maybe things have changed. I wonder what their Minimum Order Quantity is, if we tried to buy from them directly…

[Bob Moulder]

A few months ago I made a tyvek ground sheet for my MLD Duomid.

It works great but is rather heavy, so I have been looking at the various polycryo discussions to learn something about polycryo characteristics and noticed the revival of this thread.

My plan is to make a 'bathtub' design as I did with the Tyvek version, and to use some bamboo chopstick 'stays' in the corners to make the edges stay up. It occurred to me that this technique can also be used to make tie-outs that distribute forces evenly across the width of the tape, so I made a quick mock-up to test and took a few photos to illustrate. This is 0.7 mil polycryo and, while not very scientific, I can say I pulled it with quite a bit of effort and it held well and the stress lines in the polycryo were spread evenly across the width of the tape.

edit typos

[Dave Ayers]

Ace Hardware has a 62×210 film kit listed at 1.2 mils thick at http://www.acehardware.com/product/index.jsp?productId=12006452&cp=2568443.2568453.2626341.2627449 if that's not a typo.

[Matt Swider]

Folks seemed to be looking for this heavy duty material earlier this year, I recently bought one from amazon for about $13.  It weighs almost 9 oz with the edge hemmed with the double sided tape.  I failed to weigh it prior to adding the hem.  Lots of good info on this thread.  In a similar thread I asked about tape loops instead of washers, answered here,thanks.  Also asked about ridgelines, seems like the added strength is worth the weight cost.  Although I think I may try either 1/2 width or 1/3 width ridgeline.  Any additional field reports of the polycryo tarps in use?

One more thought/question.  I saw the 45 degree angle tape anchors proved 1.5x stronger than the perpindicular ones.  This would be applicable on a side tie out.  However, in the corner, a typical tie out would go out at 45 degrees with a straight piece of tape.  So maybe this is better?  But the other factor is if one hems the seam, then the angled tie out tape would be on top (at least partially) of the hem tape,so now who wins the strength contest?   So many experiments to run . . .

[Mt. Tamalpais]

I recently posted some videos on youtube testing the strength of polycro. I found 2 layers of 12″ wide hexayurt tape can be laid together, one horizontal and one vertical to make indestructible polycro.

https://www.youtube.com/watch?v=V84z8nwwIF4

 

[Michael Ray]

I was going through the polycryo threads again in prep for finally getting around to Tarp v3 for me, and I was dumbfounded that I apparently glossed over this part of Dan’s OP:

“I found out that the double sided tape has a stronger hold then the material. The polycryo sheared in half on one of the sections and the taped connection looked just like new without any slipping of the material on the tape.”

I am utterly amazed that small width of tape would have such shear strength! It honestly didn’t seem to stick all that well to me when I used it for hems. I see that others have since discovered that 3M #90 adhesive seems to work well for joining pieces also.

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