Shelter Silnylon HH Test Results
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Mar 5, 2011 at 4:22 pm #1704896David OlsenSpectator
@owareLocale: Steptoe Butte
So PU coatings weaken fabric, while silicone increases the tear strength. At what point
does this become and issue?Mar 5, 2011 at 4:33 pm #1704902Tom ClarkBPL Member
@tomclarkLocale: East Coast
Thanks for sharing the information. I thought the Mullen Burst tester used a rubber diaphram to test the burst strength if paper, film, etc., not for hydrostatic head testing.
Have you tested any other fabics (Spinnaker) for comparison?
TomMar 5, 2011 at 4:34 pm #1704903Paul McLaughlinBPL Member
You tell me – since you make tents and tarps – have you ever had a shelter fail due to fabric failure? I personally haven't had that issue, not in 40 years of backpacking/snowcamping, using many different tents and tarps, some homemade some purchased, most of them PU-coated. I've had poles fail, I've poked holes with ice axes, I pulled one corner stake loop right out of a tent because I yanked too hard trying to get out a frozen-in SMC snow stake, but I've never had a fabric failure while the tent was up. I currently have an MSR Twin peaks, which is silnylon with a PU layer, and that fabric is stout. I've had it in some strong winds above timberline, set up drum tight and it felt like there was plenty of reserve strength there. I was a little nervous about the load on my poles – wondering if the Flicklocks would handle it – but had no doubts about the fabric.
So I would guess that the point at which the fabric strength , and the coating's effect on it, becomes an issue is at lower fabric weights than we are used to seeing on the market – somewhere down in the area of Spinnaker cloth and below.Mar 5, 2011 at 5:20 pm #1704915James MarcoBPL Member
@jamesdmarcoLocale: Finger Lakes
Really great work! Thanks for sharing your results.Mar 5, 2011 at 6:44 pm #1704933
If you assume that your shelter force dissipation time is on average three times longer than a rigid surface and hit hits vertically, then the answer to your question is as follows:
2mm = 389 (Light Rain)
4mm = 2,528 (Typical Thunderstorm)
6mm = 6,450
8mm = 11,892
10mm = 18,784 (largest recorded rain drop size)Mar 5, 2011 at 6:58 pm #1704936James MoughanMember
"That is what I would define as a minimal hydrostatic head for a single wall shelter that will avoid misting in most thunderstorms"
Aha – being from the UK I'm afraid I've only just realized that the southwestern United States gets monsoon rainfall. From the literature it appears that rain intensities in the monsoon are dramatically higher than anything we experience here, and that the frequency of large raindrops increases non-linearly with rain intensity.
By contrast with the 10,000mm HH of NeoShell, EU standards for rain protection clothing demand between 800mm and 1,300mm. The old British standards demand 1,000mm. If we apply the same 'magic number' to these figures then we get HH requirements of less than 500mm, which would explain why the consensus on UK forums appeared to be that no-one had experienced misting with silnylon.
Thanks for all the information!Mar 5, 2011 at 7:31 pm #1704948
I have never had a silnylon shelter rip in a storm. The first time a sil/PU shelter rips in a storm, that is the point it becomes a BIG issue for me. Until then, if it is weaker and still does the job, that is OK with me.Mar 5, 2011 at 8:03 pm #1704956
I have only tested the shelters that I own. I am curious to see what Spinaker would test at. If there is a someone in the Bay Area who has this type of shelter and is willing to bring it San Carlos for testing, I can do it in less than 1/2 hour.
There are two Mullen variants; one of them uses hydrostatic pressure (oil rather than water) to test at very high pressures. I technically mispoke calling this a hydrostatic head test… the ones I am familiar with handle much higher pressures than most water based hydrostatic testers and that was the point I was trying to make.
ASTM D751 – TEST METHOD FOR BURSTING STRENGTH
"Standard Test Method for Coated Fabrics"
Explanation of Test Method:
The test method allows the use of either of two separate procedures. They are called 'Mullen Burst' and 'Ball Burst'. The Mullen Burst test uses a circular material sample that has been clamped over a diaphragm and inflated with oil. Pressure is applied until the fabric bursts. The pressure (in pounds per square inch) at which the fabric bursts is the bursting strength.
The ball burst test uses a steel ball attached to a tensile test machine which forces the ball through a sample of fabric that is clamped rigidly in place. The results are expressed in pounds force.Mar 5, 2011 at 8:18 pm #1704961Roger CaffinBPL Member
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> So PU coatings weaken fabric, while silicone increases the tear strength. At what point
> does this become and issue?
Basically, dunno. I have used both PU-coated nylon (60 gsm?) and stock silnylon (49 gsm) in a 4-season tent in the snow and had them both hammmered. Our Main Range country gets horrible winds and machine-gun-hail, but (so far) no fabric failures. Looking at the fabric behaviour under wind, I am not expecting any either.
CheersMar 5, 2011 at 8:22 pm #1704965
Sometimes I forget about the gloabal audience participating in these forums. I found your observation about your typical raindrop sizes in the UK and the implications for your rainwear standards extremely interesting.Mar 6, 2011 at 6:43 am #1705047Stuart RBPL Member
Although small rain drops have a low terminal velocity, when they are carried in a 50+mph wind from an Atlantic Low their impact pressure can be quite substantial.Mar 6, 2011 at 9:26 am #1705077kevin timmBPL Member
@ktimmLocale: Colorado (SeekOutside)
We spec 1500 mm. I think any of the 3k type pressure ratings on sil require large quantity buys from overseas.
My experience has been that you can get water coming through and you can get misting or condensation falling from inside. At a certain point it doesn't matter with single walls, and that point is likely somewhere around 1500 meaning that rain hard enough to penetrate 1500 rating will also cause condensation to bounce off the inside. Double wall is the only cure at certain times. A double wall doesn't need to weigh a lot. We have a DWR liner, which weighs less than 1.5 lbs on a 6 person tent and it keeps you dry in the rain, the hail, the frost, all the conditions in which a single wall will not.
KevinMar 6, 2011 at 10:33 am #1705097James MoughanMember
yes so I've noticed. :) Nevertheless, in the absence of people reporting misting in winds rather higher than that, I'm guessing that penetration varies strongly with the volume of water impacting.
So far I haven't had my Trailstar out in really filthy conditions but hopefully I can put my hypothesis to the test soon.Mar 6, 2011 at 11:16 am #1705108James MarcoBPL Member
@jamesdmarcoLocale: Finger Lakes
Assuming your numbers are correct and accurate.
But several things happen at microscopic pour densities that could shed some additional light on this subject.
1) The fabric itself has been treated with a highly hydroscopic substance, silicone. I am not sure whether this is designed to permanently, 100percently cover fabric pores or not. It may happen that way as a side effect of the treatment. Of course, coating with silicone caulk will cover the pores. One way would leave the fabric somewhat breathable. One way would not.
2) The surface tension of water is small, but at the density of the woven cloth we are dealing with, the individual unsupported area is also very small. This can contribute greatly to water resistance. And, it becomes significant in repelling a new water droplet in that few milliseconds of time it takes to readjust the molecular film, simultaneous with the impact of the drop. (I think that a portion of the ballooning under a microscope, as reported by Roger, may be surface tension and not a silicone bubble.) And, this is also why silicon bags are known to leak when in contact with anything. Like the old canvas, water surface tension makes them work.
3) The high density weaves have a two fold effect on the impact of a water drop. Along with the non, rigid nature of the cloth, the first effect will tend to break up the impact. The second effect, because we are talking small microscopic distances, funneling any impact into the pores. This will lead to very small micro droplets or misting on the inside. As Richard has said "In simple words, “IT IS UGLY AND IT SHOULD NOT BE ALLOWED” (smile)." These micro-droplets will slow very fast. The conventional two layer tent will easily absorb them.
(As much as I hate to admit it, this would make a good case for double walled shelters in heavy rain areas, like the Pacific North West or the North East.)
To help avoid these problems, I would suggest a simple coating of silicone caulk and mineral spirits at about a .2oz/yd weight, leaving any side walls as is. For tarp users, such as myself, this is not a lot of help. But for tent users, simply coating the uppers, anything over your sleeping area or beyond 45 degrees will help. Sidewalls, need not be coated. The angle of the impact should allow no real misting, no penetration.
Edited for spelling to add this note(I forgot about this, sorry):
4) The stretching of the nylon. A lot of what we interpret as abrasion can be attributed to to that. But a goodly amount can be attributed to stretching. Folding will stretch material, as will simply wadding it into a ball. Rolling it is not quite so bad, but it will still happen. And of course, that perfectly taught pitch. Anyway, I believe this will open the pores in the fabric making them more sensitive to rain.
An example of some moderate stretching: My tarp was originally 9'7-5/8" wide. After 4 years of use, somewhere between 100 and 200 nights, it now is about 9'8" at one end and 9'7-7/8" at the other. The center also has a permanent dimple from propping it up with a staff.
Another example of more extreme stretching: A somewhat larger tarp measured 10'4" at the peak. It now measures 10'5-3/8". Well over an inch of stretching. Over about 7 years, it has seen much more use…maybe 300 nights of base camp use.Mar 6, 2011 at 11:42 am #1705112a bMember
For what it's worth I have actually re-sealed my shelter with a method of silicone Caulk thinned with mineral spirits.
I was on a thru hike at the time(CDT).
I had a spinnaker fabric shelter that had 5,000 miles on it and i began to suspect misting due to abrasion wear.
I bought some oil based clear silicone caulking and mineral spirits from a trail town(Darby MT) hardware store and set up my shelter in a town's parking lot.
The silicone was thinned at a ratio of 6:1; that is 6 parts mineral spirits to 1 part silicone.
After painting the mixture on I went and had a few beers in the town tavern while waiting for it to dry.
Three hours later the shelter was just tacky to the touch so I bought some baby powder (Talcum powder) and dusted the entire shelter before packing it up.
The results were such that the spinnaker was completely water tight. The wetting of the fabric was totally eliminated.
The downside was that I had added 8 ounces to my shelter.
My mistake was using a camel hair paintbrush.
I should have used a foam brush to get a thinner more uniform coating and perhaps a thinner mixture of silicone than 6:1.
Another note: Beware of plumbing silicone.. it is waterbased and will not mix with the mineral spirits.
A lot of caulking products don't specify if they are water or oil based. However, if you check the "clean up" procedure on the tube you will be able to figure out which it is.
You want oil based caulk to mix with mineral spirits.
Another note: The hardware store in Darby only had a few tubes of clear silicone so I had to use one tube of white silicone. All were oil based and all thinned just fine but definitely changed the appearance of my tent(Looks like it's covered in frost all the time now!).Mar 6, 2011 at 1:17 pm #1705148
I suspect that the reason that silnylon shelter’s HH quickly degrades from handling is that the fabrics weaves are not uniform. The microscope photos show randomly located and relatively large silicone film islands. Possibly stuffing- and-un-stuffing causes these film islands to micro-fracture.
If so, then there may be a solvent that would not add weight to the shelter; would not damage the nylon threads; but, with stiff brushing would cause the silicone to soften and re-bond across the micro-fractures.
Well chemists, what do you think?Mar 6, 2011 at 3:13 pm #1705183Roger CaffinBPL Member
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> there may be a solvent that would not add weight to the shelter; would not damage the
> nylon threads; but, with stiff brushing would cause the silicone to soften and re-bond
> across the micro-fractures.
You want a solvent which can break long-chain polymers up in a controlled manner and then allow them to recombine after the solvent has evaporated? I don't think any such things exists, and if it did you would not want it any where near your body!!!!
cheersMar 6, 2011 at 5:55 pm #1705244
I guess I would rather add a little "repair" weight rather than grow an extra finger (smile).Mar 6, 2011 at 6:35 pm #1705262a bMember
"I suspect that the reason that silnylon shelter’s HH quickly degrades from handling is that the fabrics weaves are not uniform. The microscope photos show randomly located and relatively large silicone film islands. Possibly stuffing- and-un-stuffing causes these film islands to micro-fracture."
This is exactly what i thought happpened to my spinnaker after 5,000 miles. I was never particularly careful with it in the first place. I usually stuffed it into and out of the pack every day whether i set it up or not. Many times I used it as a ground sheet when i was cowboy camping. It took on the appearance of having been sanded with sand paper in places. Then in a Montana thunderstorm with high winds, to the point i had to brace the trekking poles, I felt rain getting through the fabric with every gust if wind.
It was not a "fatal" event. After a few hours the wind died down and i was able to stretch out and go to sleep. Yea, a little bit of moisture go on my WM ultralight but it was not a big deal.
I think for most people the abrasion factor wearing a "water proof" fabric is a non-issue. For a thru hiker using the same shelter for thousands of miles and hundreds of compression cycles it might be an issue.
I can say with certainty that the DWR finish of a Marmot Precip Jacket will degrade in as little as 20 compression cycles. After a hundred such stuffings into and out of the pack it wets out easily after an hour of rainfall. After a couple thousand miles, despite drying in a hot dryer, the DWR of a Marmot Precip is useless IMHO.
Once the DWR goes, the inner surface of the jacket becomes a moisture trap and you might as well be wearing a plastic garbage bag.
Mr. Richard, are there any specifications for the HH value of Cuben Fiber?(Smile)
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