Polycro Tarp Tested!

[robert van putten]

But, isn’t .048 inch 48 mils? Divide that by four and you get 12 mils.
If you were measuring 40 thicknesses, got a reading of .048, then divided by 40 you’d get 1.2 mils. I think.

The reading Lance got checks out, .003 inch, or three mils, for four layers, or .75 mil per layer.
Feel free to check my math guys!

– Isn’t math fun?

David, I have what looks to be the very same El Cheapo harbor freight digital calipers, which I got for ammo reloading. I was trying to read the thickness of my Frost King interior kit with it last night and I repeatedly got .002 inch, or 2 mils for one thickness of the material. I’m quite sure that is very wrong.

I gotta say that after checking this calipers I do not trust them one bit, especially for such small measurements. It's fine for overall cartridge length, maybe even bullet and bore diameter, but I don’t think that instrument is up to the Polycryo challenge!

By the by, the plastic sheeting alone from my Frost King interior 84” by 110” kit weighs exactly four ounces on an El Cheapo on-sale-at-wal-mart digital kitchen scale ( Not exactly NIST traceable ). I’d be curious to know the weight of the same size exterior kit.

Anyway, we can conclude that some folk use the thinner interior kits and some folk use the stouter exterior kits, and they all seem to work well enough?

Edited to add – I had two inches of fresh snow on my tarp this morning. It was sagging, but holding…
It will be interesting to see if it is still staying up tonight when I get home.
Also, I see the silver duct tape isn't recomended?
Why? It seems to be holding well enough on my tarp, so far anyway.

[David Gardner]

Yeah, my math sucked on that one. Apparently, so do my calipers.

[Daryl and Daryl]

My experience with duct tape is that it dries out and comes loose from whatever it is stuck to over time.

[robert van putten]

Doing a little research and have identified the following brands and thicknesses.

Ace Hardware – Most kits are .6 mil, but they do have 1.2 mil outdoor kits available, item number 5604277. I have yet to find one in store.

Scotch – 3M – Indoor and outdoor kits are .75 mil

Dennis – interior are .6, exterior are 1.2

Duck – Exterior kits are .7 mil

Frost King – They replied to my email and say the exterior kits are .75 mil

Am I missing any brands?

My tarp in the above photos is made of Dennis 1.2 mil stuff, and is holding up well to four inches of fresh snow so far.

Edited to update thickness info –

[Peter Evans]

http://www.homehardware.ca/en/rec/index.htm/Hardware/Builders/Weatherstrip/Window-Kits/64-x-10-1-2-Outdoor-Insulation-Window-Kit/_/N-2pqfZ67l/Ne-67n/Ntk-All_EN/R-I2396507?Ntt=Window+Kit

It's available in various sizes, and in a roll… 1.4 mil stuff is available, that's what I've got set aside as a groundsheet.

[Peter Evans]

http://www.homedepot.ca/product/bulk-film-84-in-x-25-tape-195/975246

pretty good deal on a roll here.

[Aaron Sorensen]

I'm thinking a huge T-P would be the best application for Polycryo.
Although it would not be something you would want to have a bunch of drunk friends in.

[robert van putten]

I couldn't for the life of me figure out what a "huge T-P" was untill I was actually typing this out. Duh.

I've made Tipis from heavy duty poly tarps and contact cement. They last for years.
They are fun and easy to make.

Lay out a big tarp –

In the center of one edge hammer a stake and tie a line to it. This line is used to mark out the circular bottom hem, and while yer at it draw a sharp W up at the top.
This gets cut out and the center V gets folded over and glues down with the top suspension line tied to it.

Mark out the big semicircle and draw out some smoke flaps in the unused corners
Cut everything out, and glue and fold over the bottom circular hem with a cord in the seam.
Cut holes in the hem when dry and tie stake down loops.

Select and trim poles

Set up the tripod and tie yer lifting pole to the top suspension line. You can see the stake down loops on the bottom hem.

Warming up in a partially erected tipi

Quite comfortable in there. I’ve lived for weeks in a tipi and know someone that spent a Canadian winter in one.
Sorry about the thread drift, I couldn’t resist.
I’m not sure heat shrink material is best for a tipi because the best feature of a tipi is the ability to build a fire inside it!

[robert van putten]

We have gotten about six inches of snow this week, and will probably get six more by Monday.

The load on the tarp is tremendous and this 3/32 Atwood cord stretches quite a bit!
But knock the snow off and the tarp snaps back up. I’ve knocked the snow off only once because I want to see the tarp flattened with snow to load test it!

I've also made a second tarp out of a Frost King interior kit.
I did hem this much lighter material with the included double sided tape, and I used some big faucet washers for grommets. I used six inches of tape per tie out and as there are eight tie outs on the side and two in the center, that's a total of five feet of tape. It turns out this isn't duct tape but rather an old roll of "canoe repair tape" if there is any difference –

I used the same Atwood 3/32 cord and the ridge line is 29 feet long, because I like to be able to easily tie off to trees.

Total weight of finished shelter, 7.2 ounces!
Not bad for such a big tarp. I used a patio door sized kit, 84 inches wide and 110 inches long, so this is an 7 foot by 9 foot tarp.

[David Gardner]

Robert,

Very cool. Any plans to spend the night under your shelter?

The polycryo is pretty durable stuff. Sure wish I could find a source for 1.5 – 2 mil sheets. Anyone out there have any ideas?

Did you use the 84" x 110" Frost King interior kit for the new tarp? Do you plan to pitch it in the snow also?

[robert van putten]

Yep, The new one was made from a frost king interior kit. I'll be setting it up in the snow tomorow!

I intend to use the big one I made on trips with my nephews and the smaller and lighter tarp as a solo shelter. No real plans to sleep outside right now, it's hard to do when I have a perfectly warm and dry bed not very far away, and with a wife in there to boot…

I guess I'm getting lazy in my old age?!?

The 1.4 mil Comfort Plus stuff Peter found seems to be about the stoutest, and I bet it's pretty durn good stuff. I'm impressed with the 1.2 Dennis stuff I used in my first tarp, I didn't even hem that one.

I have no idea how thick the Frost King interior kits are and am guessing the same 7.5 mil as their exterior kits? I'll ask 'em in another email.

This Frost King kit film weighed 4 ounces alone. The tape hem added another 1/2 ounce.
The rest is the tape, washers and cord.

[David Gardner]

Peter, I can't figure out if the 1.4 mil polycryo comes in the 84" x 25' roll or the window kits, or maybe both. Where is your groundsheet piece from?

Thanks,
David

[David Gardner]

Last night we had a big storm with high winds, and after almost 6 months of constant outdoor exposure part of my prototype polycryo tarp finally failed. The tape tie-out at the ridge line on one end separated from the other tape it was attached to. None of the tape-to-tarp connections failed, only the one tape-to-tape connection. It is a construction detail that I only used on this prototype; the tarps in production have only tape-to-tarp connections. Still, 180 days/26 weeks of exposure isn't too bad, and is probably equivalent to many years of regular use. Now I will torture test to death one of my production tarps, and see how that goes.

[Peter Evans]

"Peter, I can't figure out if the 1.4 mil polycryo comes in the 84" x 25' roll or the window kits, or maybe both. Where is your groundsheet piece from?

Thanks,
David"

David, It is available here (Canada) in both forms at "home hardware" stores… I'll check soon if I get a chance and get a pic and use my QRcode reader.

[Michael Ray]

Cool! Was there a reason you had done tape-to-tape on this one? I assume this is the nylon sail repair tape? I have 2 rolls on their way here.

Do you have an estimate of wind speed and direction in relation to the tarp?

I'm thinking of making a big A-frame like your's for my son and I to use as an alternate shelter for our summer trip when there aren't any skeeters.

[David Gardner]

Yes, it is the nylon sail repair tape. I did tape-to-tape for two reasons:

1. To make the triple tarp I joined two 84" x 110" pieces of polycryo at the ridgeline using the sail repair tape, then added the tie-out. There was no un-taped tarp to attach the ridge line tie-out to.

2. Lack of experience building and testing tarps. My technique has evolved so that now the tie outs are made from the same pieces of nylon tape (one on top, one underneath) that I use to join the polycryo sheets.

Gusts were up to 45 mph, blowing at 45* to 90* directly across the ridge line of the tarp. That's lot of surface area and the wind loads really add up.

Have fun making your big A-frame. The basic tarp is pretty simple and straight forward, but the end flaps are tricky. Let me know if you want construction details and I'll send photos and/or sketches in a PM.

[Daryl and Daryl]

For me this whole thread has been a lot of fun. I ordered some polycryo and hope to join in.

Thanks for all the input. I've read every post.

[robert van putten]

The seam in the big tarp I had set up in the snow ( pictured above ) failed when my wife was knocking the snow off it. She got under it and was vigorously whacking it to knock the snow off it because the snow had built up along the sides so that it couldn’t just slide off anymore, but has to be propelled some distance away. She didn’t know there was a seam in the middle, and it parted. It was made with two runs of the double sided tape that came with the plastic.

The plastic had stretched a little along that edge, but after it was dried out and warmed up we were able to put it back together with more tape. This time I also reinforced the seam with bits of the duct tape I used to make the tie-outs.

I am convinced these tarps are sturdy enough for most conditions but of course they probably would not be my first choice for winter trips, at least up here!

I think my preference is for a simple flat 7 x 9 foot tarp made from a patio door kit with no seams. I think long term freezing weather may affect how well the tape holds?
I don’t think I’d want a shaped tarp made this way, but end flaps are probably OK.

I’ve had my smaller tarp made from the indoor patio kit set up out in the snow for some time now and despite the fact it is half as thick as my big tarp it is holding up well to heavy snow loads with no sign of failure. At under half a pound and under twenty bucks, I think this tarp is just the thing for day hikes where I don’t intend to stay out overnight but think some shelter might be wise just in case, for three season trips where bugs don’t present much of a problem and the like.

[Michael Ray]

Thanks for the info. It's nice to know they'll hold a fair amount of snow load.

I'd also guess the adhesive on the provided tape isn't superior to some of the other tapes we're using (especially if from an indoor kit like mine is). It seemed fine for "hems" on the edge. Just personal observation and opinion, nothing scientific to back that up.

My door kit is 7×10 and I plan to make just a simple flat tarp instead of my normal half pyramid for my son and I to use as an alternate shelter this summer when there aren't skeeters wreaking havoc.

I've considered a shaped design but my engineering mind leans toward the KISS side of things. Maybe if I ever get to use a shaped tarp some day that seems superior for my needs I may give it a try. No reason it shouldn't work though the taping could become challenging (more so than sewing I'd guess).

[Nathan Meyerson]

I'm having a hard time finding a source of thicker 1.2 or heavier shrink film in the US besides the Dennis outdoor kits. Anyone able to secure a source in the US? A 25' roll would be perfect.

[Dale Wambaugh]

I wonder if the heat shrink stuff they use for winterizing boats will work?

[Michael Ray]

Interesting thought. Did a quick search and I'd say it wouldn't be practical.

"This film is a heavy duty shrink polyethylene available stock in BLUE, WHITE, or CLEAR in 6 MIL and 7 MIL, from 12 feet wide to 36 feet wide."

Quite thick so it will be heavy, polyethylene based so I'd bet it stretches more than polyolefin and it would be hard to find small quantities when rolls are 12' wide min. Not too expensive really. I saw a 14' x 150' roll for $147.

[Pete Staehling]

Are there any problems with Polycro shrinking in the hot sun? Do you need to preshrink it or anything??

[Jerry Adams]

preshrink….

hmmm…

Make a tarp and then use hair dryer to shrink it. It would form catenary curve. Actually, maybe better than a catenary because it would take into account the reality of your particular tarp.

somebody try this : )

[Michael Ray]

No need to preshrink. It needs much hotter temp than sunlight to shrink.

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