[TheForge] interesting project

[Andrew Vida]

"terry l. ridder" wrote:

> 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.

	I fyou can get most of it off with elbow grease, perhaps
	you can use a heat gun (carefully, mind you) to drive off 
	the volatile components of the tar that may be left.  What
	remains is usually a dry and brittle mass that perhaps you
	could wire brush away from the brick and stone.  Not an
	optimal solution perhaps, but as you say, there appear 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.

	Or again, use a heat gun and scrape most of it off whilst
	gooey.  Liquid N may work well, but would the users be
	able to safely use it?  It's dangerous stull to get on
	one's skin.

	As for patinas, there are a million recipes out there.  I have
	a book entitled "The Colouring and Patination of Metals" or
	something to that effect, by Rowe.  It contains a bit under 400
	recipes and procedures for patinas on copper based metals.
	You should be able to pick and choose.  The problem may be
	application in the environment rather than in a studio.  Some
	of the patinas are less than straightforward in their use, but
	I suppose with sufficient ambition anything is possible.
> 
> 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.

	Get the main mass removed and perhaps a powerwash would do the
	rest?  Just a thought.

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

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

	Jeeez...