[at-l] Tyvek Tidbit

["Mayer, Jim" <JMayer@crt.xerox.com>]

Not too long ago there was quite a bit of activity about using Tyvek
Housewrap (and other formulations) for tarps.  For some reason that I'm
not too sure about, I just ran a series of little experiments with the
stuff.

Basically, I was interested in how to attach tie outs to a sheet of
Tyvek.  The "standard" technique is to tie a cord in with a sheet bend.
I've used this, and it worked fine.  It is a bit ugly though, and is a
pain to do anywhere but at the corners.  I decided to play with grommets
and sewing in a loop.

Once Tyvek starts to rip it is pretty well gone, so I didn't even bother
working with a single sheet of Tyvek.  Instead I looked at reinforcing
it.  I tried four different forms of reinforcement:

(1) sandwiching a corner of a sheet between two pieces of Tyvek using a
spray adhesive.

(2) Same as (1) but using Barge Cement (a contact cement).

(3) Sandwiching a corner between two pieces of duct tape.

(4) Sandwiching a corner between two pieces of the adhesive backed
ripstop nylon you can buy for repairing tents.

I tried all four techniques with grommets and confirmed my general
impression of grommets... they tear out.  However, in all four cases the
reinforcing fabric failed and there was no evidence of the adhesive
giving way.

I also kept track of how much (subjective) force I had to apply before
the grommet failed.  It seemed that the ripstop sandwich held much
better than the other three reinforcing techniques.

I then sewed a loop of 3/4" nylon webbing onto a ripstop sandwich
reinforced corner of a piece of Tyvek.  The whole thing looked like
this:

wwwwwwwwwwwwwww
w      rrrrrrrrrrrrrr
w      ttttttttttttttttttttttttttttt
w      rrrrrrrrrrrrrr
wwwwwwwwwwwwwww

Where "w" stands for the nylon webbing, "r" stands for ripstop nylon
tape, and "t" stands for Tyvek.  I used heavy polyester thread in a box
stitch.   The stitched pattern looked like this:

xxxxxxxxxx
xx      xx
x x    x x
x  x  x  x
x   xx   x
x  x  x  x
x x    x x
xx      xx
xxxxxxxxxx

I then attempted to pull out the loop.  The loop held really, really
well.  I had to use much more force than for any of the other fasteners,
and when a failure finally occurred it was in the Tyvek.  The whole
corner ripped off, about a half inch past the reinforcing ripstop.
There was no evidence of the stitching pulling out, or of the adhesive
giving way.

From this, I conclude that the reinforced loop was actually stronger
than the Tyvek sheet itself.  And that, of course, is as much as one can
ask.

-- Jim Mayer
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