Ralph,

Assuming this is an early cavity wall, i.e. about 3/4" mostly open cavity
between the face brick and concrete block backup and that the wall performed
well initially, I would be reluctant to install a vapor barrier where there
wasn't one to begin with. I fear trapping the moisture naturally being
driven out of the building behind the barrier. I suggest analyzing the wall
section for where condensation will form during normal ambient conditions -
my mechanical engineers do this for me all the time. This will identify
where the condensation will form in the wall and it is based on the thermal
characteristics of the particular wall. Mold is a somewhat legit concern but
not the only result of condensation within a wall that we should be
concerned about. There is also plaster deterioration and steel corrosion
too.

I recommend looking for the real cause of the leaks. Are they systemic or
discrete leak locations. Do you really need to strip the wall just to stop
the leaks? Don't forget, you will need to seal around all those brick ties.
But, if you do need to reface, I suggest using a vapor permeable waterproof
membrane similar to the "damproofing" they used to install on the backup
walls.


Eric Hammarberg
Director of Preservation
Sr. Associate
LZA Technology
641 Avenue of the Americas
New York, NY 10011-2014
Telephone: 917.661.8160 (Direct)
Mobile: 917.439.3537
Fax: 917.661.8161 (Direct)
email:  [log in to unmask]


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, March 25, 2004 1:58 PM
To: [log in to unmask]
Subject: [BP] Vapor Barrier Question


Alright, boys and girls, I have another pain-in-the-ass technical question,
this time regarding vapor barriers and flexible membrane flashing inside
masonry walls.

I am working on a couple of c. 1950-60 NYC residential buildings, into which
I want to stop water penetration.  What I have recommended in the past is
removal of face masonry (in both these cases, brick) and installation of
flexible membrane flashing on the outer face of the backup wall (concrete
block), followed by rebricking and installation of weeps, drainage mat, etc.
The theory is that whatever water migrates inwards through the face brick
will be stopped and drain down the face of the Bituthene, and out the weeps.

One of my least-favorite contractors said yesterday that there have been
concerns that sealing up an entire building in this way may prevent moist
INDOOR air from passing through the wall and outwards, and that mold may
grow as a result.  What this alleged individual says is that they have
installed one "course" of Bituthene at shelf angle level to drain water out
and flash the shelf angles, and above that they install Tyvek so that the
moist indoor air can pass through the Tyvek instead of being blocked by the
Bituthene and being trapped forever inside the wall.  This guy claimed that
the Tyvek was sealed (including horizontal lap joints) and nailed or glued
to the backup wall, so that condensation forms on the INSIDE face of the
Tyvek.

 Seems to me that sealing the Tyvek, esp. at horiz joints, will trap
moisture, too, and trap it at the INTERIOR face of the Tyvek, where you
really don't want it.  For the Tyvek to do you any good, it seems to me that
the horiz. Tyvek joints have to be left open so that moisture that condenses
will run down the interior face of the Tyvek and eventually be conducted to
the Bituthene and drained out.

OR am I full of shit about how condensation inside walls works, and
specifically on which plane within the wall it condenses; I have a feeling
that inside moisture condenses at a different plane within the wall than
cold oudoor air condenses.

Please advise, and thanks.

Ralph


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