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Verlager
2005-10-10, 01:11
I sleep in a hammock and I regularly use a tarp pitched as an A-frame. I have never strung a 12' line under the top of the "A", instead I just rely on the slight tension at the two high tie-off points (not the ground tie downs) to maintain the tarp's profile.

I suspect, however, that such a line would add needed support to the tarp in the event that rain or snow (or wind?) added extra strain to the system.

What do professional tarp users do? Is option B really better for the tarp?

A. Tie the two main tie offs with a few lbs. pressure to keep the tarp from sagging ....

-- or --

B. Use the two main tie offs tied gently, and run a line all the way under the tarp for extra support.

youngblood
2005-10-10, 08:24
My tarp experience is with silnylon and I don't know if it is different with different materials. I wouldn't recommend the clothesline approach (your method B) for several reasons. First is tarp tautness and the related flapping, sagging, etc. Second is the possibility of rubbing and excessive wear against a taut clothesline. Third is that silnylon is waterproof only to a certain pressure and I have been told that the taut clothesline underneath it will compromise its waterproofness where the silnylon makes contact with the clothesline.

Youngblood

Verlager
2005-10-10, 09:47
Thanks, your answer makes good sense. I'll abide by it when using silnyl tarps.

But it might be satisfactory with nylon taffeta tarps.

Seeker
2005-10-11, 01:51
when i made a homemade silnylon tarp from 48" wide stock, i cut two pieces 10' long, sewed them together to get an 8' wide tarp, and backed that seam with nylon webbing. when i use it over my HH, if i'm hanging a-frame style, i can rely on that seam adding strength... there's also a tieout in the middle, again sewn into the nylon, so i can hang it from there too, again relying on the strength of the sewn in webbing. the 8 x 10 tarp, with lines and webbbing, is about 17 oz, though i haven't reweighed it since resurfacing it with a silicone/mineral spirits mixture.

Verlager
2005-10-12, 12:21
the 8 x 10 tarp, with lines and webbbing, is about 17 oz, though i haven't reweighed it since resurfacing it with a silicone/mineral spirits mixture.OK, I think my beloved JRB tarp needs to be resurfaced. How do I get the silicone/mineral spirits mixture? I suppose then I just use a large paint brush to slosh it on. Any tips?

Sgathak
2005-10-12, 15:09
Silnylon is waterproof only to a certain pressure? Ummm... them how do people make no-drip waterbags with the stuff?

Hog On Ice
2005-10-12, 17:05
Silnylon is waterproof only to a certain pressure? Ummm... them how do people make no-drip waterbags with the stuff?

as a guess its because the water bag is a constant fairly low pressure whereas a big raindrop hitting the tarp will have an impulse pressure spike when it hits that is somewhat higher and depending on the size of the drop the impulse may be high enough to force some water through the silnylon.

Sgathak
2005-10-12, 17:58
Silnylon is totally vapor impermeable isnt it? People use it as groundsheets because it doesnt wet-through under pressure. Im having a hard time seeing how any water could pass through even under fairly high impulse.

Id be more inclined to think that rain is knocking loose any condensation that might be forming and its comes down as a fine mist.

Anyway, I dont really care, Ive just never heard that Silnylon is pressure sensitive so I was curious.

Seeker
2005-10-13, 22:35
OK, I think my beloved JRB tarp needs to be resurfaced. How do I get the silicone/mineral spirits mixture? I suppose then I just use a large paint brish to slosh it on. Any tips?

somebody posted a site for this after i did my tarp. it was a great article on working with the stuff. he recommends using a 3:1 ratio, by weight.
http://jwbasecamp.com/Articles/Silnylon1

but i got a tube of GE clear caulking and a gallon or so of no-vapor mineral spirits from walmart. i mixed the entire tube in a bucket with about 2 qts of the mineral spirits. takes a long time to dissolve it, so stir it good... i hung my tarp on the clothesline and just painted it with a wide foam brush on a nice hot breezy day. after one side was done, it dried in about 20 minutes. then i did the other side. ended up with about a quart left.

youngblood
2005-10-13, 22:36
What makes you think that silnylon water carriers don't leak a little? I don't have one but wouldn't be surprised if they did. My silnylon packcover does (or did, I recently 'recoated' the top portion of it) in heavy rains and my tarps mist through as well. Anyway, silnylon does have its limitations and Jim Wood has an excellent article that puts numbers on some of them http://jwbasecamp.com/Articles/Silnylon1/index.html . I've seen similar numbers from various other sources over the years as well. I have heard of using spray on silicone on tarps to improve or 'refresh' the waterproofness of silnylon tarps. I think that it eventually just washes off but a can of it is about $3 and it is pretty easy to apply.

Youngblood

youngblood
2005-10-13, 22:49
Seeker, I didn't see your post until after I posted mine.

A few of things I've done to make the process a little easier is to do like you did; keep the mixture thin (it thickens pretty quick so you may want to add a little mineral spirits from time to time), use a jelly/pickle/etc jar with a good lid, shake it to mix (glass make it easier to see how well it is mixed and shaking is a whole lot easier than stirring) and to use a foam brush.

Sgathak
2005-10-14, 03:00
"What makes you think that silnylon water carriers don't leak a little?"

Ummm... Experience?

Ive used a few, and I know many others who have as well.

youngblood
2005-10-14, 09:07
"What makes you think that silnylon water carriers don't leak a little?"

Ummm... Experience?

Ive used a few, and I know many others who have as well.That's a good answer... no drips as well, even if you rub the bottom while it is full of water?

Sgathak
2005-10-14, 14:01
Not unless theres a hole in the material.

You get drips while the outside of the bag is wet... but hang it in the sun for a while (so the outside can dry) and a well maintained silnylon bag will hold water without dripping.

Seeker
2005-10-14, 14:05
Seeker, I didn't see your post until after I posted mine.

A few of things I've done to make the process a little easier is to do like you did; keep the mixture thin (it thickens pretty quick so you may want to add a little mineral spirits from time to time), use a jelly/pickle/etc jar with a good lid, shake it to mix (glass make it easier to see how well it is mixed and shaking is a whole lot easier than stirring) and to use a foam brush.

no problem... i think you're the guy who sent the original link a few weeks ago anyway... good idea there about the pickle jar... i've got my leftovers in a coffee can, and it doesn't seal all that well...

i've used the can of spray silicone before... what was funny was that as i was painting, the smell was identical to the stuff in the can...

Verlager
2005-10-14, 17:49
It just sounds like a mess, smearing that slurry on the tarp. I will try it next year in a paint sprayer, which will atomize it and apply it evenly. That is, assuming I can get the stuff thru the nozzle.

Seeker
2005-10-15, 00:57
not at all... that's why you use a foam brush... you can do a couple feet wide with each dipping of the brush, and maybe get 2 brush widths (is that a word?) high... doesn't drip much, but maybe that's just me being neat...

stuff you used in a paint sprayer i'm guessing would be really thin...maybe a lot less silcone/oz of mix...

CanoeCamper
2005-11-26, 17:36
Ummm... Experience?

Ive used a few, and I know many others who have as well.

Ok, fill your sack with water and poke your finger into it. Not much pressure, just enough to "dent" the side a little. I'll bet water leaks from the pressure point. Now imagine a pressure point all the way across where the clothesline touches the top of the tarp.

Sgathak
2005-11-27, 00:08
If the bag is made of sylnylon, it will not leak unless there is a hole in it.

Same thing with a tarp.

It is impermiable.

youngblood
2005-11-27, 10:55
There are limits to 'waterproof'.

Think about wrist watches or cameras... some are waterproof to depths of 3 feet, some 10 feet, some 30 meters, some 50 meters, some 100 meters and then others are waterproof to depths of 300 meters. What do you think will happen to a camera that is waterproof to 10 feet if you take it SCUBA diving to a depth of 120 feet... it will likely be full of water when you surface. On the other hand, if you took it snorkling where you didn't dive more that 10 feet deep you would expect it be fine... unless you waved it around as quickly as possible because you would have added a dynamic pressure to the weight of a 10 foot column of water.

Same situation with silnylon, it is specified to be waterproof to a certain pressure but it is not near the pressure that tradition high quality tent flys are specified to. Silnylon does not necessarily, or even usually rip or tear when it waterproofness rating is exceeded, with rain it just comes through like a fine mist. With a bag of water, water would just seep through.

Some manufactured water bags might apply a coating of polyurethane coating to increase the waterproofness like The North Face does with the silnylon fly on their Tadpole 23 tent. Check out the add copy on this Campmor link about the additional coating: http://www.campmor.com/webapp/wcs/stores/servlet/ProductDisplay?productId=39165038&memberId=12500226 . The coating is added to the silnylon so that the silnylon will be waterproof to The North Face's internal specifications for waterproof tent flys.

Sgathak
2005-11-27, 16:41
Whatever. Nevermind.

Silnylon apparently is utterly waterproof for everyone but you.