Date:         Wed, 30 Nov 94 13:03:22 EST
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         sas@opus.xyplex.com (Scott Sminkey - Sustaining Eng Group)
Subject:      Re: Waterproofing Canvas A No-No

Derek mentioned the problems with waterproofing canvas (makes the canvas
unbreathable and makes the upstairs of the camper pretty clammy), and
reiterated that canvas is naturally waterproof. For those who are wondering
why, here's the answer from back in my boy scout days...

Canvas is actually a very, very fine mesh of fibers. When canvas is dry,
there are small spaces (the mesh) between the fibers, hence canvas is
breathable. When canvas gets wet, the fibers swell and close up the mesh,
keeping water (and air) from passing thru. If you poke firmly on the side
of a wet canvas sheet, you will stretch a small area of the fibers, opening
up the mesh and causing a leak. If oil, waterproofing or water repellency
stuff, or even a lot of dirt gets on canvas, it can keep the fibers from
swelling up when wet, so it's a good idea to keep the canvas clean, using
water and a mild soap if necessary, but be sure to rinse thoroughly. When
canvas gets very, very old, it might not swell up when wet. Your choices
then are to replace it, or waterproof it and accept the problems pointed
out by Derek.

- Scott
  91 Camper
=============
Scott Sminkey				email: sasminkey@eng.xyplex.com
Software Sustaining Engineering		voice: 508 952-4792
Xyplex, Inc.				fax: 508 952-4887
295 Foster St.				(Opinions, comments, etc. are mine,
Littleton, MA 01460					not Xyplex's...)
       "Ollie ollie oxen-free! Pass it along." - Swami Bill