[TheForge] Re: interesting project

[Joe Chadwick]

>
>problem. interesting project, solution may not be that easy.

Quick & easy solutions in cases like this might invite more and worse problems.
This is admittedly the way-too-complicated answer, but this is most of my 
day-job.


>the house is a historic house in dekalb, illinois.

Is there a named historic certification or district that would trigger an 
approvals/ review process?

>the house was built
>in the late 1800s or early 1900s. it is an eggshell colored terra cotta
>brick and stone mansion.

I'm not familiar with the grades of brick clay common in Illinois, but you 
need to know some specific things about the porosity and absorption rate of 
the material before you get too far. Then you need to know about how the 
brick was fired.

>the main roof the part copper and part tile.
>the main roof is fine. the problem is the single story, flat roof,
>"breakfast" porch. someone in the last century tarred the roof. they
>were not to careful as to where the tar oversprayed. roughly fifty feet
>of copper sheet roofing to partial covered with tar. approximately 35
>square feet of stone work and brick work is either covered with tar or
>has severe overspray.

Before you go removing it, does anybody know why it was put there in the 
first place? (did the roof leak? the seams? the joints?)
This "tar" could be coal tar, roofing asphalt, or a form of rubberized 
asphalt. Each have a slightly different removal protocol.
If it is a low slope roof, and in fact sprayed, it suggests a rubberized 
bitumen emulsion. The over-spray could have been an attempt to either 
liquid-flash the roof-house joint or provide some degree of moisture 
protection to the side wall from snow accumulation. If this goes away, and 
the removal process affects the surface, the moisture accumulation in the 
masonry is the quiet start of a disaster.

>given the age and composition of the brick and stone work acid or base
>cleaning is out of the question.

Maybe, maybe not..

>in researching several restoration
>sites on the web which especially deal with stone and/or brick masonary
>historical building there seem to be few options.

I haven't found good sources for this work on the web either.


>copper sheet on roof. there are several reasonable restrictions. attempt
>to preserve the original copper patina if at all possible. if not
>possible propose a way to artifically recreate the patina to match the
>original existing copper patina elsewhere on the roof. they are aware
>that once the tar is removed from the copper sheet that the newly
>exposed copper will need to be artifically aged.

There is an abundance of patina formulations, I think you have that covered.

>the national park
>service site on restoration of historical sites suggests using liquid
>nitrogen to freeze the tar and chip it off the metal with plastic or
>nylon tools. that seems like a reasonable possibility.

  whether or not it is Coal tar or asphalt or rubberized bitumen makes a 
big difference.


>the masonary ( stone and brick ) is a different problem. the moisture
>content of the brick and stone would seem to prevent the use of liquid
>nitrogen. the fear i have would be that will freezing the tar and
>hydroscopic moisture content of the mansory would also freeze and cause
>the masonary to crack or spall. abrasive removal is out of the question
>since the stone work is soft stone. so how to remove the tar from the
>masonary. again in researching the web several commerical products were
>suggested. upon reading the msds they all contain dichloromethane
>(methylene chloride), xylene, and ethyl benzene. dichloromethane and
>ethyl benzene are listed as carcingens. the safety measures required to
>work with these chemicals and given the close proximity of neighboring
>houses really prohibits their use. the hazardous waste disposal would
>also tend to be cost prohibitive.

Depending on the solvent and porosity of the substrate and ambient vapor 
pressure, one can drive the stain even deeper into the material with some 
of these solvents.


>two web sites listed using kerosene to remove the tar. they suggested
>soaking heavy paper towels or cotton rags in kerosene and draping them
>or securing them to the areas and let the kerosene soaked paper towel
>or cotton rags through capillary action dissolve the tar and soak it
>into the paper towel or cotton rags. this would appear to be a workable
>solution. yet another solution was to use an extremely small nozzle on a
>liquid nitrogen hose and freeze the tar in small sections and remove it
>a bit at a time.

 From what I can gather, 1) Find out why this stuff is where it is, 2) if 
it is just careless initial installation, try gentle mechanical removal, 
determine the nature of the "tar" and  use a poultice to draw out the stain.
The baking soda blasting can be effective depending on the depth of the 
stain. We've used it on our buildings with good success. Dry ice blasting 
is also done, but the setup costs would be prohibitive.


>i am interesting in observations, comments, suggestions, etc.

Tell them to find an Architect that specializes in restoration and 
construction failure mitigation.


>btw, this project has to be done by the weekend. there is a party at
>this house on saturday of roughly 150 people.

I hope that party is sufficiently interesting to keep everyone's focus on 
the party. I doubt that this can be resolved in a week....or recalling one 
of Frank Lloyd Wright's bromides, "Doctors can bury their mistakes. All an 
Architect can do is to advise the client to plant ivy." ...Flower pots on 
the roof?