>All of our tests have indicated that the Jahn product we approve for
patching has the best vapor transmission rate of all the products we have
tested to date.  This is why we specify it.
 
Mary Jablonski<

While you are quite correct that Edison Custom 45 vapor transmission rates
are typically about 40% lower than Jahn's vapor transmission rates, it is
absurd to specify products on this basis alone.

First of all, how do you define OPTIMUM vapor transmission rate? Is maximum
automatically optimum?

 What if the trade off for a higher vapor transmission rate is a product
with a liquid permeability than is thousands of times higher than the
natural stone, leaking-through under wind-driven rain conditions within 5
minutes? 

What if it shrinks 2 or 3 times more? What if its bond strength is 70%
lower? 

Why does nothing else that normally represents good engineering practice
get even the slightest priority when evaluating compatibility and
performance of repair materials for masonry?

If you want to make high vapor transmission rates the one and only priority
for specifying a repair, why not just leave a hole in the wall?

Mike E.