helping a friend clean a university building. windows haven’t been cleaned in years. where the glass meets the aluminum frame the caulking or gasket is spreading over the glass at the top and bottom. it is black and sticky. turned my tucker brush grey and black.
we were using tsp and soap. is there something that would work better??
What your dealings with is butyl or " 440 " glaring tape. It seals and holds the window in place. It that has oozed out over years of exposure from the sun. It is nasty stuff to deal with. Best things to do is spray it down with glass cleaner and use a sharp razor blade to peel it off and if some residue remains clean it off with varsol and a rag.
Hope this helps.
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Sorry meant " glazing tape ".
thanks @redant i am sure your are right about it being butyl tape. with that info i did some further research and testing (on the tucker brush, not the windows) found that mineral spirits dissolves it very effectively
thanks again 
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