[TheForge] interesting project

Tue May 20 09:32:01 2003

Terry, If the schedule will allow, try patience. I have had fairly good
success in chipping tar loose from masonry in cold weather. The colder it is
the better. Unfortunately we are in the wrong season. Freezing at -20 is
much less drastic that liquid nitrogen.

Mike Graf

"terry l. ridder" wrote:

> 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 ><>
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