[TheForge] interesting project

[terry l. ridder]

hello;

a couple weeks ago i received a call from a person who asked me if i
would look at a problem with a house that was being restored and he felt
that i would either know how or know of someone who would be able to do
the work. yesterday, monday, i took a break from the seemingly
neverending legal nightmares i went and looked at the house and the
problem. interesting project, solution may not be that easy.

the house is a historic house in dekalb, illinois. the house was built
in the late 1800s or early 1900s. it is an eggshell colored terra cotta
brick and stone mansion. 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.

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

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. 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.

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.


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.

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

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


-- 
Terry L. Ridder ><>