Some inaccuracies: Re: [pct-l] More about tents and tarps.

[calliger@infolane.com (R.J.Calliger)]

Oh- some references-

Jardines discusses briefly the "waterproofness" of various materials
and Bibler shamelessly claims totally waterproof:

http://www.rayjardine.com/projects/projects.shtml  - follow the links to net tub floor.


http://www.bibler.com/text/facts.html#anchor63120 - go to Bibler home ==there
is a lot of discussion (albeit biased) regarding tent facts.

Happy trails,

Rich


At 4:40 PM -0800 4/29/01, John Mertes wrote:
> 
 
>
> While you may get condensation inside your tent, a ground cloth underneath the tent floor will have no effect on the condensation inside your tent. How can it? 
>  
>

ALMOST ALL MATERIALS in use today are measured by PSI for waterproof/resistance
pressure and flow rate in grams of water per square meter per 24 hours.
These are industry standards. Standing your tent in a pool of water and/or
saturated ground for several days will prove the point (with warm bodies
inside!)

ALMOST ALL MATERIALS are porous to some degree therefore.

A ground cloth provides that extra degree of added PSI resistance and
reduction in flow rate to stop condensation and migration through 
the bottom of the tent.

SOME MATERIALS such as heavy rubber (not usually found in backpacking
tents) are non porous of course and will also withstand several thousands
of pounds of water pressure therefore are truely waterproof.

ALMOST NO MODERN tent material is truely totally waterproof as almost all the
materials use are porous OVER TIME- and that time is **usually** in the
range of 1-2 days. And as a tent ages floor threads spread, fabric weave
opens allowing more vapor and water thru in stormy conditions.

FINALLY- try it for yourself- same rainy conditions, same temps, same
tent, etc..with and without a ground cloth.

OR- if you have a high pressure water source you can prove it to yourself.
 
HOWEVER- very few tents can make the claim some do about total waterproof
and non-floor condensation. Bibler (one I owned) has a 70 denier taffetta 
that is laminated to 1.5 mil polyurethane film. BUT- Bibler (the designer)
claims it is only "more waterproof than any coating "... but in the
same marketing lit they advertise it as totally waterproof. Go figure.
(My experience on the snow and in the mud it needed a ground cloth)

PRACTICAL experience dictates that in a 2-day storm water seeps in the
bottom in irritating quantities. And in a 2-3 day base-camp set up in
dry- but with  somewhat damp ground and without a ground cloth
there is sufficient flow (IN MOST TENT MATERIALS) to condense out
in the floor.