This is a very familiar thread, of course. The question of coatings on brownstone is one I have been arguing about for nearly 30 years, and still represents an area where I believe that preservation professionals need to get their heads out of their books and go out into the real world and have a look around.

I formed my opinions on this subject after walking up and down the streets in Boston in the mid-80's, when whole neighborhoods of badly deteriorating rows of brownstone houses were in the process of being revitalized. There, side-by-side, block after block, sat rows of nearly identical facades, built at one time, with the same stone and design. Some had never been touched, as far as I could tell, and they were in typically bad shape  - exfoliating sills and cornices, etc. Some had been shmeared with cement plaster, and when that plaster went bad it took an awful lot of stone with it - worse, perhaps than the ones that had never been touched. But the ones that were painted were in relatively good shape. Some looked like they had been painted decades earlier and with who knows what, and generally just less stone damage. Maybe Judy Selwyn will disagree with me.

I am just a chemical engineer, so I haven't read every Columbia University thesis or NPS study (and have had some significant criticisms of some that I have read). But I know how to read psychrometric (humidity) charts and run condensation calculations, and I have to say that the whole question is dicey. I think it's a lot harder to wreck a sandstone building with paint than most preservationists assume (or are told). I think bad roofs and gutters and lack of maintenance are the real culprits most of the time. If you don't have tons of water pouring into the wall system, letting it out just isn't that big a deal.

At the T&C concrete conference last Spring there was an excellent speaker from Princeton University on the subject of freeze-thaw damage. At the conclusion of the talk, a well-known histo-presto professor got up and made a comment to the effect that the preservation community may have been wrong in opposing the use of clear water repellents on masonry buildings, because as they examine actual sites, 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.

As for brownstone - I don't favor the total shmear approach, because it just isn't a stone building any more after that. Repair of localized damages in a mechanically and aesthetically compatible way, followed by stabilization of all surfaces with the correct clear treatment has effectively preserved our earliest brownstone projects for nearly 30 years, and counting.

Edison Coatings, Inc. 
Michael P. Edison 
President 
3 Northwest Drive 
Plainville, CT 06062 
Phone: (860) 747-2220 or (800)341-6621 
Fax: (860)747-2280 
Internet: www.edisoncoatings.com 
         www.rosendalecement.net 
E-Mail: [log in to unmask]

> 
> Paint on brownstone can provide a similar vapor barrier layer as stucco and though the stone may have been perfectly fine to begin with the paint layer itself can be a cause of damage. It is for this reason that conservators when faced with a question to coat, or not to coat, when pushed to a coating will tend toward one that is considered 'breathable' meaning, that the coating will allow evaporated water molecules to move through it. Mr. Edison can explain how that works. These coatings, generally, are intended to inhibit water from the exterior to move through to the interior. In my experience non-breathable coatings are applied all over the place on masonry and though they may look pretty for a while they continue to result in deterioration of the underlying masonry hidden from view.
> 
> 
> Also, masonry is delightful for the variety of hue, texture, surface and reflection of light. A coating tends toward a monolithic appearance. The visual character of a masonry building is altered with the application of either stucco or coatings, and for the most part these alterations can only be reversed at great trouble and expense, if at all.
> 
 

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