----- Original Message -----

From: [log in to unmask] href="mailto:[log in to unmask]">Edison Coatings

To: [log in to unmask] href="mailto:[log in to unmask]">[log in to unmask]

Sent: Monday, January 26, 2009 1:05 PM

Subject: Re: [BP] Removing fake brownstone

Pat wrote:

>

> Most specs I have seen are almost totally based upon the ultimate breathability of a material. I think it is a disservice to even use the term “some capacity to breathe” when everything I see is about the “material” specified being as transparent to the substrate as possible.

OK, so our basic disagreement is taking shape. I think specifications that focus too narrowly on permeability, often excluding other critical considerations, are emblematic of what is wrong with preservation practice.
>

> “deeper drying by slowing down the drying rate”

>

> I really need a better description of this and would prefer a time frame, while I think this may have merit in a lab environment I don’t know if anyone has yet been able to tell mother nature how to set up her schedule. In principle I get it, in practice, I don’t see it but am always open to information. Also depending on the stone wet/dry cycles can be as devastating or more so than freeze thaw.

TCH, TCH!! Thou knowst not from whence thou speakst on this one. This approach has been used proscriptively with great success to dry out saturated masonry buildings. Time frame: Anywhere from 10 days to 5 years, dpending on construction details.
>

> “Brownstone is generally so porous that the water drains through it too quickly to achieve total saturation”

>

>  --- unless you put a coating or less permeable product on which proves the point about moisture build up because of the rapid movement of moisture through the brownstone but not the coating. At the interface you have vapor turning to moisture because of dew point and you have moisture turning to ice because of extremely low temperature, and because it fills the pores any expansion will cause deterioration. I will however agree with Mike that too many failures are blamed on freeze that, wet/dry is just as much to blame depending on the stone, typically poorer quality stones.

> 

Alas, most things are not this black and white - this is way oversimplifying both the process and the conclusions. You do not have an absolute point where permeability is good, then reduce it a little, and all of a sudden just lose everything, like rolling off the edge of a table. I have a great deal of respect for the few in the field that have expressed an understanding of the nuance of all this, and they generally agree that when it comes to permeability, it's like horseshoes or hand grenades - close is good enough. Let's face it, if we want to carry permeability to the absurd, nobody will patch the stone, paint it, stucco it or replace it - maximum permeability is achieved by blowing giant holes in the wall.

Mike E

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