Polycro Tarp Tested!

[Michael Ray]

David Gardner shared another tape option – nylon sail repair tape. Not too expensive and he says it's lighter than duct tape.

[Michael McMillan]

I found this a few months ago and I think that it addresses the problems people in this group are having with your guy lines.

It basically says that after the tape leaves the edge of the tarp, you fold the tape inwards in thirds so that no sticky is exposed to the rope, yet you also don't weaken the tape.

http://www.youtube.com/watch?v=PktX1SxDTQs

-Michael

[David Gardner]

Much lighter, and has great adhesion even when cold and wet.

Just made my third polycryo tarp using the ripstop nylon sail repair tape. Uploading photos of it pitched "high" for headroom and "low" for weather protection.

Didn't see the thread on using nylon washers but stumbled upon the same idea while wandering the aisle at the local hardware store. I used 1" O.D. washers on the side tie-outs and 1.125" O.D. washers on the ridge ends, which distribute the forces well.

My tie-outs are taped to both sides of the tarp membrane. I cut 8" pieces of the sail tape and fold them in half, tape to the underside of the membrane with the fold 1" outside the hem, stick the washer down, and then fold the tape on top of the washer and membrane. Corner tie-outs are at 45 degree angle to edges; side tie-outs are perpendicular. The wide tape spreads the forces very well.

You can see in the photo that I also use a small loop of shock cord at the side and corner tie-outs, both to keep a nice taught pitch and also to provide some give when subjected to high winds.

The big washers at the ridge line tie-outs are connected to each other by a ridge line cord running between them. Separate tie-out lines are knotted to the outside edge of the washers. This way all of the ridge line tension is maintained by the cord and not the membrane, and the membrane stays in place instead of being free to move on the cord.

7' x 9' tarp with 10 tie-outs (4 on each side, 2 at the ridge ends) weighs 5.4 oz.

With 40' of cordage (200 lb. kevlar bow cord), 2 graphite poles, 2 Nano stakes for the ridge line cords and 8 titanium shepherd's hook stakes for the side tie-outs, total weight is 12.3 oz.

I favor the A-frame style because it's roomy, but I'm trying to figure out a good way to enclose the ends with flaps and/or vestibule. The trick is accommodating different pitch angles for the sides. Here is a prototype with overlapping flaps that velcro to each other:

[Nick Gatel]

You guys are about 40 years late to the party. I used polyethelene tarps quite a long time ago. Surprisingly durable. My experiments yielded that anything thinner than 4 mil did not hold up long. Having used polycro a lot as ground sheets, I wouldn't expect much out of that material as a tarp if under 4 mil too.

Did a lot of experimenting with adhesive tie-outs too. A real weak point. What does work are visklamps.

By the time you reinforce those polycro tarps with tape and use extra cords you might find that a spinnaker tarp is lighter. Cuben will definitely be lighter.

But, BRAVO for your experiments.

[David Gardner]

I remember using polyethylene "tube tents" with the same ball and hoop rig back when I was in Boy Scouts. For sure, it works.

The polycryo weighs about 0.57 oz/yd, so there are a couple of grades of cuben fiber that are lighter I believe, 0.51 sq/yd and 0.34 oz/yd. They're also $30/yd, so $210 for a 7' x 9' tarp versus $10 for the whole polycryo sheet.

The polycryo sheet by itself weighs 4.0 oz and with tie-outs it weighs 5.4 oz, so all the tape tie-outs and nylon washers only add 1.4 oz.

The polycryo is designed and intended for extended extreme weather exposure. It's pretty durable. The first tarp I made from it has been set up outside since September and it's hanging tough. The sail repair tape remains intact as well. The conditions here in Northern California are not extreme by any means, but it's had plenty of sun and rain exposure, and now we'll see how it does with freezing temperatures at night.

No question cuben fiber is stronger and more tear-resistant, but based on my experience the polycryo should be fine for careful 3-season use.

[Nick Gatel]

I have a lot of experience with "minimalist" shelters. We need to make sure we can stay warm and dry in poor weather. With wind and rain one can die from hypothermia in 50F temps. I would never trust my life on a polyethylene or polycro tarp less than 4 mil. Plus using a smallish tarp requires skill and experience. Just be careful. Often in deserts and mountains the weatherman can be wrong and predicted good weather doesn't happen. My opinion.

With that thin polycro I can just envision it collapsing without the hiker waking up. It could probably suffocate someone like a dry cleaning bag can. Again, IMO.

[Michael Ray]

Polycryo is much better than polyethylene as a shelter material. The only thing that should have any serious chance of damaging it is having a stick fall on it where it would puncture. It will stand up in 50 mph winds. If you're going to go out in more extreme weather, then , yes, I'd take a more orthodox tent.

FWIW, I've been through a couple hailstorms in my 1 mil polyethylene tarp (space blanket grade, not the cheaper stuff they make dropcloths with – would definitely want 3 mil or better with that).

[David Gardner]

Here is a picture of tarp prototype #1 that's been set up in my yard since September. Basically, I'm torture testing it to death. Going to see how long it takes for some part to fail, whether the membrane loses integrity or tape stops adhering or ??? So far, so good, even on the un-hemmed sides (later versions are hemmed all the way around). The only thing I've had to do is re-set the stakes a couple of times when the ground was soaked and they started to pull out.

The only failure mode that seems likely to me is high winds, which might tear the membrane or blow the whole thing down. So I don't think there is any real danger of it settling onto a sleeping hiker and suffocating him or her.

[Michael Ray]

Nice, David. In my experience the tape was the weakest point. I found the 3M 2120 did a fair job of adhering to the membrane even after 2 months of constant exposure to summer sun. I'd guess your nylon sail tape would fare even better. That is why I didn't bother using the 3M 8959 tape on my second prototype even though it was significantly stronger. I didn't need the extra strength but did need the long-term integrity. I didn't test the shockcord, but I'd guess it would weaken over time and UV exposure as well.

What are the worst winds you've had so far?

[David Gardner]

We've had some blustery storms here with gusts to 30 mph. Worst weather is yet to come, so this should be interesting.

[Dan Johnson]

FWIW, I'm still using my first tarp I made with this stuff. I'm very cautious about my camp spot. I try to always be in the trees or at least behind a good wind break. I'm not sure how everyone else is doing their ridge line but since I run the cordage under the middle of the tarp I've been able to get a real tight pitch every time. Doing it this way also really helps with any deflection from wind since it puts most of the pressure on the cordage.

My only concern at this point is the repeated folding/rolling on the material after unpacking/packing it. But it's still going strong :)

[David Gardner]

Came up with a good idea for tarp ends/flaps for weather perfection. Tested it in the rain yesterday and last night. Taking it to the Gathering of Gear Geeks this weekend.

[David Gardner]

Weight of the Solo Tarp with vestibules, including two 8' ridge line tie-out cords and eight shock cord side tie-outs is 169.7 grams/6.06 oz.

[Michael Ray]

Nice job, David. I'd be interested on hearing more details on the door attachments and how you deal with varying pitch widths.

[David Gardner]

The doors are attached on the outside edge with the double-sided tape that comes with the polycryo package and on the inside edge with sail repair tape. As the pitch becomes wider the vestibules become shallower and don't stick out as far. At the widest pitch they are almost vertical.

[Michael Ray]

I can see the lines of sail tape for what you're calling the inside edge. A pic would help me understand what you mean by outside edge. It appears they are inset from the end a couple inches, which is what I would have done as well. It sounds (and looks) like you aren't connecting the flaps in any way (or is that what you meant by outside edge?), just putting a guyout on the corners and staking to the same point?

[David Gardner]

Michael,

The "outside" edge of the end flaps is the side opposite the sail tape. Tried to take a picture, but the tape is so transparent you can't see it. If this explanation doesn't do it, I can make a sketch and send it to you as a PDF attachment to an email.

The flaps are velcroed to each other at the bottom where they meet. One flap is staked to the ground, the other is the "door". May extend the velcro all the way from ground to peak. Working on a new refinement of the flaps based on this weekend's experience at the Gathering of Gear Geeks.

[robert van putten]

So I picked up some window film to play with last weekend –
I got what I could find, some exterior stuff by Dennis and some interior stuff from Frost King.

I see that Dennis lists their interior film as .6 mil, and their exterior stuff as 1.2 mil thicknesses. Frost King does not apparently list the thickness of their stuff, anybody know what it is?

I made a rather huge tarp out of the Dennis material. It is about 120 inches long by 105 inches wide, with one seem in the middle tapped with two runs of the supplied double sided tape. I used ordinary silver duct tape and steel washers as that is what I had on hand. I used Atwood 3/32 “tactical” cord for the tie outs ( four per side ) and ridge line.
I did not tape-hem the tarp. Probably a mistake?
I set it up in the deep snow in my yard, and my wife helped by throwing snowballs at it while I was working on it. The tarp does seem to deflect snowballs well enough.
She thinks it might do well for a night or two but is betting the tape tie outs will rip the material in short order. We will see!
Total weight ( not counting my high tech 2×4 snow stakes I set it up with ) is 12.5 ounces.

I’ll post a picture or two of the setup when I get the time.

I am curious, has anyone used the thin interior material successfully, either for ground cloths or tarps?

I reckon I might as well go ahead and make a tarp out of the interior kit I have and hang it in the yard and see how well it lasts. The stuff sure is light, but it may well prove to delicate for use as a shelter?

[robert van putten]

OK, here are some pics. You ever notice how hard it is to get decent photos of something transparent?

I'll leave the tarp up and sooner or later we'll see how it does in some serious snow.

[David Gardner]

Robert,

Don't know the thickness of the Frost King interior or exterior, but I assume it is similar to the Dennis.

Interested to see how your tarp does under a snow load. It has a pretty flat pitch; steeper sides would probably help it shed the snow. Also, are you running a ridge line cord, or just the double-sided tape? A ridge cord would definitely help with loads. Hemming too. Can't beat the stakes though.

Look forward to pictures after a good blizzard.

David

[robert van putten]

Oh yeah, it has a ridge line. The seam is perpendicular to the ridgeline in the middle of the tarp, not running down the ridge line.

The weather has been unusually nice latley, might have to wait till next week but I'm sure the tarp will get to see some snow before long. I bet it slides off the slick polycro pretty easily.

So I gather you use the exterior kits then.

[David Gardner]

Yes, I use the Frost King exterior kits. Trying to source some thicker polycryo, but no luck yet. If I can get a hold of some I will post it here.

[Michael Ray]

I'm using indoor kits. Duck brand doesn't list a thickness. The Scotch one someone gave me says 0.75 mil.

[Lance M]

The Duck brand I purchased at Walmart last spring appears to be .75 mil. Here's what I got when I measured four thicknesses of Duck brand:

Hope this helps.

[David Gardner]

Inspired by Lance, I got .048" when I measured four thicknesses of Frost King exterior polycryo. So it seems to be 1.2 mil, like the Dennis exterior product.

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