RalFS,

It's not so much about the backer rod as it is the sealant.  If the sealant
was a good material to begin with, installed per manufacturer's spec, with
the proper techniques, then the backer has little to do with water
infiltration.  Still, I would never use open cell -- yes, it's a sponge.

Closed cell rod has been used in joints for decades.  It comes in a
gazillion sizes and even a variety of colors.  Its main positive properties
are: being polyethylene -- a bond breaker -- sealant won't stick to it,
which is good because that allows movement without the sealant tearing;
being round in section, which, along with surface tooling, creates the nice
double concave profile -- maximum area of adhesion + minimized section of
sealant -- for improved elastic action; and it fixes the depth at which the
sealant is placed.  Also, when properly installed, the rod is under
compression and provides a "back-up" water and air seal for the sealant.

You do have to be careful that it is not a material that off-gasses in
service, that will cause bubbles and other nasty reactions that cause
sealant failure.  But that is very rare today.

If it's still available, you should get a copy of the sealant manual printed
by the Sealants and Waterproofers Institute.  It's a good primer and pretty
much covers what every contractor and artichoke needs to know.

Bruce Popkin

> -----Original Message-----
> From: Ralph Walter [SMTP:[log in to unmask]]
> Sent: Sunday, June 09, 2002 8:00 PM
> To:   [log in to unmask]
> Subject:      Re: Backer rod inquiry
>
> Alright, I have another urgent technical question for everybody to ignore:
>
> I am investigating leakage into an EIFS-clad building, constructed in 1997
> in
> the Northeast.  A key problem appears to be the use of what has been
> called
> (by a source I consider highly reliable) open cell backer rod at the
> sealant
> joints.
>
> Can anybody direct me to (or give me anecdotal) info on backer rod,
> specifically the difference between open and closed cell (it appears to me
> that open cell looks like foam rubber and/or a sponge; whereas closed cell
> looks like carpet padding); how long has closed cell been available (did
> open
> cell in fact precede closed?); are there legitimate uses for open cell or
> is
> it all useless shit at this point (and if so, since when?).
>
> Thanks ever so much.
>
> Love and kisses,
>
> Ralph
>
> --
> To terminate puerile preservation prattling among pals and the
> uncoffee-ed, or to change your settings, go to:
> <http://maelstrom.stjohns.edu/archives/bullamanka-pinheads.html>

--
To terminate puerile preservation prattling among pals and the
uncoffee-ed, or to change your settings, go to:
<http://maelstrom.stjohns.edu/archives/bullamanka-pinheads.html>