I'm no geologist, but in class I learned that some sandstones are permeable, allowing moisture to migrate, some not. If you coat the facade to prevent moisture from getting in, you might be preventing it from getting out. Aside from gutters, there might be moisture migrating from inside the building through the stone and (micro) freeze- thawing behind the moisture barrier.

How to prevent that is another question.

Larry2


---- Gabriel Orgrease <[log in to unmask]> wrote: 
> Edison Coatings wrote:
> >
> > I am just a chemical engineer
> >
> And I am just a guy that gets to play with stuff.
> 
> I agree that control of water flow through maintenance of gutters, 
> leaders, roof systems etc. is way more of a factor in the deterioration 
> of brownstone facades than coatings. Though I really am solidly against 
> the wholesale use of cut-n-stucco techniques.
> 
> I have encountered situations, one in particular, where the sandstone 
> (not brown in this case) was coated so many times by maintenance staff 
> that it was the coating that held the stone together. Once the coating 
> was removed the stone crumbled, whereas everywhere else on the facade 
> where maintenance could not conveniently reach the stone was in 
> noticeably better, though admittedly poor, condition. So, I would prefer 
> appropriate maintenance if it is to occur at all. In my experience 
> though knowledge is not very well communicated to maintenance. Which 
> brings up questions as to how knowledge of anything gets disseminated 
> into the built environment. Many times experts are not brought in to see 
> evidence in the field as there is no motivation to involve them -- then 
> the question is how do they learn?
> 
> > If you don't have tons of water pouring into the wall system, letting 
> > it out just isn't that big a deal.
> >
> Yeah, all you need is good flow, a few well placed holes.
> >
> > ...they just aren't seeing the predicted damage. DUH! But hey, don't 
> > acknowledge those of us who questioned the conclusions on this 
> > subject 25 years ago.
> >
> I agree with your sentiment re: the back-n-forth on clear coatings. It 
> is curious to me that a quarter century can go by and yet there is no 
> conclusive consensus. One expert doctor will say it is good to beat 
> children, another expert doctor will say that it is not. Personally I 
> find the lack of consensus, and the constant reiteration of pro and con 
> to be the more interesting subject.
> 
> I remember a time when to say 'abrasive blasting' was suicide and that 
> was when I was playing with plastic media to remove epoxy paint from 
> granite at Carnegie Hall. Then came micro-abrasives and soda blast and 
> all sorts of chummy stuff.
> 
> ][<en
> 
> 
> 
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>

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