Mike:

Lets not get too logical. You know that the general process of specifications
writing is to find something that worked once and then use it over and over and
over whether it makes sense for the next, next, next project or not. Otherwise
each time the person writing the specs would have to think about the individual
project. If they do that, they may then be open to liability for having thought
rather than providing a standard response. It also means that they have to know
enough about the project, the existing materials, the processes, the
deterioration of materials, what caused the deterioration, repair material
options ... to be able to make a reasonable decision.

Do you expect them to understand how to determine an  appropriate level of
surface prep for the existing condition of a material?
...
and then
Expect them to select an appropriate repair material based on more that two
criteria, color and ???? vapor transmission rate.

I'll bet you leave hay on the roof for Rudolf, don't you.

Bryan
PS: My vapor transmission rate changes due to temperature and humidity. Is this
also true for masonry patching materials?
=======



"Michael P. Edison" wrote:

> >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.