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How much waterproofing is enough?


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  • #1305678
    Jesse Anderson
    BPL Member

    @jeepin05

    Locale: Land of Enchantment

    I'm looking for a new tent to replace an ancient one that failed spectacularly on the trail recently. I've noticed a pretty big difference between companies in how much waterproofing they use.

    I've seen anywhere from 1200mm on the floor to 3000mm on the floor and from 1200 to 1800 on the fly. My question is, what is considered enough. At what point do you get the none-too-pleasent fine mist come through the fly during a hard rain? What is enough waterproofing to prevent moisture seeping through the floor when I put a knee down on it?

    I know there is no one right answer, but I'm just trying to get a feel for the overall consensus of the group here.

    #2008460
    Nathan Watts
    BPL Member

    @7sport

    "What is enough waterproofing to prevent moisture seeping through the floor when I put a knee down on it?"

    Divide your weight by the surface area of your knee.

    #2008469
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    Sheild silnylon from thru-hiker has been waterproof for me for floor. Richard Nisley measured HH 3500 mm.

    http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=44977&disable_pagination=1

    #2008472
    michael levi
    Member

    @m-l

    Locale: W-Never Eat Soggy (W)affles

    You can have 100000000000 waterproofing and still be soaking wet, Technique and common sense beat numbers.

    #2008477
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    True enough but I've had floors from other silnylon that leaked, which I managed with, but it's better if the floor doesn't leak when you're on wet ground

    #2008479
    Jesse Anderson
    BPL Member

    @jeepin05

    Locale: Land of Enchantment

    @ Nathan I understand the math behind what you're saying, but how does that translate to the HH of a fabric? ie the maximum pressure exerted by my nee is roughly 20ish PSI, I would have no idea how many mm of water in a column that translates to (all manufacturers use the HH spec).

    @ Michael That may be true, but the opposite is also true. Technique and common sense will never be able to make up for a fabric that is underspec'd. I figure a tent is the one piece of gear that I really need to count on. If my shelter fails at its primary purpose, there is no point in bringing it along. There is no technique that will overcome a tent fly that mists water when heavy rain and hail hit. That would be like saying the size of the pores on your filter make no difference as long as you know how to use it and you follow all the rules of filtering. In both cases, if those microscopic holes are too big and things get through, you're going to have a bad day!

    #2008481
    Nathan Watts
    BPL Member

    @7sport

    HH is just another way of expressing pressure. 20psi is about 14,000 mm of water.

    #2008483
    Jesse Anderson
    BPL Member

    @jeepin05

    Locale: Land of Enchantment

    Thanks Jerry, but I don't think I'm ready to take on building my own shelter right now. Will be looking to purchase something pre-made.

    #2008488
    Greg Mihalik
    BPL Member

    @greg23

    Locale: Colorado

    1 psi = 27.707 inches of HH
    20 psi = 554.14 inches of HH

    1" = 25.4 mm
    554.14" =14,075 mm HH

    ..more or less

    The one step conversion is 1 psi = 703.758 mm HH

    #2008517
    Richard Nisley
    BPL Member

    @richard295

    Locale: San Francisco Bay Area

    Jesse,

    Regarding floor HH requirements, I will use my 190 lb and 70" tall body as an example to answer your question regarding knee pressure. When kneeling, ~310.09 inches are supporting my weight; the pressure exerted on the fabric is thus 18.42 PSI (12,794 mm H2O or 125kpa).

    No manufacture, that I am aware of, uses that high of a floor HH. Look at the Hilleberg expedition tent floors; they use material that tests 7,000 mm H2O (68.6 kpa and 10 PSI).

    There is a simple reason why Hilleberg can use lower HH fabric / coating than the pressure exerted from my knee. The water under my knee / fabric would need full containment to generate 18.42 PSI pressure. In the vast majority of the cases, the ground displaces some of the water away from the fabric.

    #2008522
    Max Dilthey
    Spectator

    @mdilthey

    Locale: MaxTheCyclist.com

    I'm curious as to the answer to what (I think) is a relatively simple question.

    Is there a consensus on what the most practical HH is for tent floor and fly?

    #2008530
    Richard Nisley
    BPL Member

    @richard295

    Locale: San Francisco Bay Area

    Jesse,

    The international standard for classifying a tent fly as rainproof is 1,500 mm H2O MINIMUM. USA manufactured silnylon averages 1,200 mm H2O for the best material commonly available. That is close enough for most people doing UL backpacking.

    Again I will use Hilleberg expedition tents as an example of what is required to address the worst case (maximum required). Their expedition tent flies test 3,000 mm H2O. There are some US vendors and material combinations being sold for UL backpacking that I tested > or = 3,000 mm H2O for the fly.

    #2008535
    Jesse Anderson
    BPL Member

    @jeepin05

    Locale: Land of Enchantment

    Max,
    I knew I would be stirring the hornets nest with my question. It was inevitable. :) One could hope it would be an easy question, but I've found that on this forum, there is no such thing. That's just the way it is when you have so many different backgrounds and experiences.

    Richard,
    Thanks for the info. If the standard says 1500mm is waterproof, that sounds like a good place to start for me. The tent I retired was a nearly 15 yr old Kelty that finally gave all she had. It wasn't near as light as what is available today. Even if it means a few extra ounces I think I'll verge on the safe side and go with something on the higher end of the range.

    #2008642
    James Marco
    BPL Member

    @jamesdmarco

    Locale: Finger Lakes

    Well, it sort of depends on what you do, and, where you are.

    For State/National parks, there is often not a lot of choice in camping spots. Low-lying areas are usually prevalent where people and cars have compressed the soils. In a heavy rainstorm, the site is often one big puddle. In this case I use an Exped Sirius. It has a 10,000mm bathtub style floor. It has been through 5 days of continuous rain, but never leaked. It was sitting in a 2" deep site-wide puddle and didn't leak. Would I take it backpacking? No. It weighs 5.5pounds. This is for getting to the ADK's and for comming home, often at a state campsite.

    I also have a mesh tent and tarp that weigh a little under two pounds (including lines, but no stakes.) Stakes bump the weight up to just over 2 pounds. In spring/fall (when the weather says cooler nights) I often just take the tarp. Backpacking is different because you can select the site you want to set up on. A slight mound, or raised area will keep the grass/duff floor dry, generally. If you anticipate a hurricane, a larger mound works better. (Yes, I have been out in a hurricane and stayed dry at night.) I recommend a small can of bug spray to keep ground insects down. Saturating a bandana with bug spray will last about a week if you keep this in a baggie, taking it out and spreading it under your bag before going to bed. Fleas, chiggers, spiders, etc all can be an anoyance at night and if they get into your bag. Mosquitoes, and the rest are usually covered by permethrin in my cloths, often, these are placed on top of my bag to dry.

    Hiking in the rain, at least in the ADK's, is difficult. Slipery roots and rocks can cause all sorts of falls. It alsways slows you down. Usually, by 1000-1100 things have dried up some. Just in time for the afternoon rains at around 1600-1700. Being the first one on the trail means wet pants, then socks, then shoes on a slipery trail. I often wait till 0900 to get going…

    The UL polycro or similar (painters drop cloths, tyvec) have a way of becomming punctured easily. I quit using them about 5-6 years ago. My pad works well enough as a ground cover. This year especially, the heavy and frequent rains have left the woods quite wet. Everything is damp, all the time, when I am out. My pack weight often increases for a day or two after I leave, due to this. Water to drink is NO problem this year.

    Soo, it really depends on where you are camping. Often a pine tree wiill have a dry area near the root bole. I like to set up there. Sometimes you can find a dryer area in the woods to set up. This often means raking up some duff to fill in low spots for my bed. Downed smaller branches can be used, too. Just cover them with leaves/duff. For the canopy, 1500mm is not enough, sometimes misting right through the fabric. New tarps will often get a coating of 20-30/1 mineral spirits/caulk. I believe this raises the HH to about 2500-3000mm for a couple ounces in weight.

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